ARM920T Technical Reference Manual - Complete

ARM920T
(Rev 1)
Technical Reference Manual
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
ARM920T
Technical Reference Manual
Copyright © 2000, 2001 ARM Limited. All rights reserved.
Release Information
Change history
Date
Issue
Change
31st January 2000
A
First release
5th September 2000
B
Second release
18th April 2001
C
Third release
Proprietary Notice
Words and logos marked with ® or ™ are registered trademarks or trademarks owned by ARM Limited, except
as otherwise stated below in this proprietary notice. Other brands and names mentioned herein may be the
trademarks of their respective owners.
Neither the whole nor any part of the information contained in, or the product described in, this document
may be adapted or reproduced in any material form except with the prior written permission of the copyright
holder.
The product described in this document is subject to continuous developments and improvements. All
particulars of the product and its use contained in this document are given by ARM in good faith. However,
all warranties implied or expressed, including but not limited to implied warranties of merchantability, or
fitness for purpose, are excluded.
This document is intended only to assist the reader in the use of the product. ARM Limited shall not be liable
for any loss or damage arising from the use of any information in this document, or any error or omission in
such information, or any incorrect use of the product.
Figure 9-5 on page 9-12 reprinted with permission IEEE Std 1149.1-1990, IEEE Standard Test Access Port
and Boundary-Scan Architecture Copyright 2000, by IEEE. The IEEE disclaims any responsibility or liability
resulting from the placement and use in the described manner
Confidentiality Status
This document is Open Access. This document has no restriction on distribution.
Product Status
The information in this document is final (information on a developed product).
Web Address
http://www.arm.com
ii
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Contents
ARM920T Technical Reference Manual
Preface
About this document .................................................................................... xvi
Further reading ............................................................................................. xx
Feedback ..................................................................................................... xxi
Chapter 1
Introduction
1.1
1.2
Chapter 2
Programmer’s Model
2.1
2.2
2.3
Chapter 3
About the programmer’s model ................................................................... 2-2
About the ARM9TDMI programmer’s model ............................................... 2-3
CP15 register map summary ...................................................................... 2-5
Memory Management Unit
3.1
3.2
3.3
3.4
3.5
3.6
3.7
ARM DDI 0151C
About the ARM920T ................................................................................... 1-2
Processor functional block diagram ............................................................ 1-3
About the MMU ........................................................................................... 3-2
MMU program accessible registers ............................................................. 3-4
Address translation ..................................................................................... 3-6
MMU faults and CPU aborts ..................................................................... 3-21
Fault address and fault status registers .................................................... 3-22
Domain access control .............................................................................. 3-23
Fault checking sequence .......................................................................... 3-25
Copyright © 2000, 2001 ARM Limited. All rights reserved.
iii
Contents
3.8
3.9
Chapter 4
Caches, Write Buffer, and Physical Address TAG (PA TAG) RAM
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
Chapter 5
About the ARM920T coprocessor interface ................................................ 7-2
LDC/STC .................................................................................................... 7-5
MCR/MRC .................................................................................................. 7-9
Interlocked MCR ....................................................................................... 7-11
CDP .......................................................................................................... 7-13
Privileged instructions ............................................................................... 7-15
Busy-waiting and interrupts ...................................................................... 7-17
About the ETM interface ............................................................................. 8-2
Debug Support
9.1
9.2
9.3
9.4
9.5
9.6
iv
About the ARM920T bus interface ............................................................. 6-2
Unidirectional AMBA ASB interface ............................................................ 6-3
Fully-compliant AMBA ASB interface ......................................................... 6-5
AMBA AHB interface ................................................................................ 6-21
Level 2 cache support and performance analysis .................................... 6-23
Trace Interface Port
8.1
Chapter 9
5-2
5-3
5-4
5-6
Coprocessor Interface
7.1
7.2
7.3
7.4
7.5
7.6
7.7
Chapter 8
About ARM920T clocking ...........................................................................
FastBus mode ............................................................................................
Synchronous mode .....................................................................................
Asynchronous mode ...................................................................................
Bus Interface Unit
6.1
6.2
6.3
6.4
6.5
Chapter 7
About the caches and write buffer .............................................................. 4-2
ICache ........................................................................................................ 4-4
DCache and write buffer ............................................................................. 4-9
Cache coherence ..................................................................................... 4-17
Cache cleaning when lockdown is in use ................................................. 4-20
Implementation notes ............................................................................... 4-21
Physical address TAG RAM ..................................................................... 4-22
Drain write buffer ...................................................................................... 4-23
Wait for interrupt ....................................................................................... 4-24
Clock Modes
5.1
5.2
5.3
5.4
Chapter 6
External aborts ......................................................................................... 3-28
Interaction of the MMU and caches .......................................................... 3-29
About debug ............................................................................................... 9-2
Debug systems ........................................................................................... 9-3
Debug interface signals .............................................................................. 9-5
Scan chains and JTAG interface .............................................................. 9-11
The JTAG state machine .......................................................................... 9-12
Test data registers .................................................................................... 9-19
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Contents
9.7
9.8
9.9
9.10
9.11
9.12
9.13
9.14
9.15
9.16
Chapter 10
AMBA signals .............................................................................................. A-2
Coprocessor interface signals ..................................................................... A-5
JTAG and TAP controller signals ................................................................ A-7
Debug signals ........................................................................................... A-10
Miscellaneous signals ............................................................................... A-12
ARM920T Trace Interface Port signals ..................................................... A-13
CP15 Test Registers
B.1
B.2
ARM DDI 0151C
ARM920T timing diagrams ........................................................................ 13-2
ARM920T timing parameters .................................................................. 13-16
Timing definitions for the ARM920T Trace Interface Port ....................... 13-26
Signal Descriptions
A.1
A.2
A.3
A.4
A.5
A.6
Appendix B
About the instruction cycle summary ........................................................ 12-2
Instruction cycle times ............................................................................... 12-3
Interlocks ................................................................................................... 12-6
AC Characteristics
13.1
13.2
13.3
Appendix A
About the AMBA test interface .................................................................. 11-2
Entering and exiting AMBA Test ............................................................... 11-3
Functional test ........................................................................................... 11-4
Burst operations ...................................................................................... 11-11
PA TAG RAM test ................................................................................... 11-12
Cache test ............................................................................................... 11-15
MMU test ................................................................................................. 11-19
Instruction Cycle Summary and Interlocks
12.1
12.2
12.3
Chapter 13
About TrackingICE .................................................................................... 10-2
Timing requirements ................................................................................. 10-3
TrackingICE outputs ................................................................................. 10-4
AMBA Test Interface
11.1
11.2
11.3
11.4
11.5
11.6
11.7
Chapter 12
9-42
9-43
9-44
9-45
9-48
9-51
9-54
9-62
9-63
9-64
TrackingICE
10.1
10.2
10.3
Chapter 11
ARM920T core clocks ...............................................................................
Clock switching during debug ...................................................................
Clock switching during test ........................................................................
Determining the core state and system state ............................................
Exit from debug state ................................................................................
The behavior of the program counter during debug ..................................
EmbeddedICE macrocell ..........................................................................
Vector catching .........................................................................................
Single-stepping .........................................................................................
Debug communications channel ...............................................................
About the test registers ............................................................................... B-2
Test state register ....................................................................................... B-3
Copyright © 2000, 2001 ARM Limited. All rights reserved.
v
Contents
B.3
B.4
B.5
Cache test registers and operations ........................................................... B-8
MMU test registers and operations ........................................................... B-18
StrongARM backwards compatibility operations ...................................... B-30
Glossary
vi
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
List of Tables
ARM920T Technical Reference Manual
Table 2-1
Table 2-2
Table 2-3
Table 2-4
Table 2-5
Table 2-6
Table 2-7
Table 2-8
Table 2-9
Table 2-10
Table 2-11
Table 2-12
Table 2-13
Table 2-14
Table 2-15
Table 2-16
Table 2-17
Table 2-18
Table 2-19
Table 3-1
Table 3-2
Table 3-3
ARM DDI 0151C
Change history .............................................................................................................. ii
ARM9TDMI implementation options ......................................................................... 2-3
CP15 register map .................................................................................................... 2-5
Address types in ARM920T ...................................................................................... 2-6
CP15 abbreviations ................................................................................................... 2-6
Register 0, ID code ................................................................................................... 2-8
Cache type register format ...................................................................................... 2-10
Cache size encoding (M=0) .................................................................................... 2-11
Cache associativity encoding (M=0) ....................................................................... 2-11
Line length encoding ............................................................................................... 2-12
Control register 1 bit functions ................................................................................ 2-12
Clocking modes ....................................................................................................... 2-14
Register 2, translation table base ............................................................................ 2-14
Register 3, domain access control .......................................................................... 2-15
Fault status register ................................................................................................. 2-16
Function descriptions register 7 .............................................................................. 2-17
Cache operations register 7 .................................................................................... 2-18
TLB operations register 8 ........................................................................................ 2-19
Accessing the cache lockdown register 9 ............................................................... 2-22
Accessing the TLB lockdown register 10 ................................................................ 2-23
CP15 register functions ............................................................................................. 3-4
Level one descriptor bits ........................................................................................... 3-9
Interpreting level one descriptor bits [1:0] ............................................................... 3-10
Copyright © 2000, 2001 ARM Limited. All rights reserved.
vii
List of Tables
Table 3-4
Table 3-5
Table 3-6
Table 3-7
Table 3-8
Table 3-9
Table 3-10
Table 3-11
Table 4-1
Table 5-1
Table 6-1
Table 6-2
Table 6-3
Table 6-4
Table 6-5
Table 6-6
Table 6-7
Table 6-8
Table 7-1
Table 9-1
Table 9-2
Table 9-3
Table 9-4
Table 9-5
Table 9-6
Table 9-7
Table 9-8
Table 9-9
Table 9-10
Table 9-11
Table 9-12
Table 9-13
Table 9-14
Table 9-15
Table 9-16
Table 9-17
Table 9-18
Table 9-19
Table 10-1
Table 11-1
Table 11-2
Table 11-3
Table 11-4
Table 11-5
Table 11-6
Table 11-7
Table 11-8
viii
Section descriptor bits ............................................................................................ 3-11
Coarse page table descriptor bits ........................................................................... 3-12
Fine page table descriptor bits ................................................................................ 3-13
Level two descriptor bits ......................................................................................... 3-16
Interpreting page table entry bits [1:0] .................................................................... 3-16
Priority encoding of fault status ............................................................................... 3-22
Interpreting access control bits in domain access control register ......................... 3-23
Interpreting access permission (AP) bits ................................................................ 3-24
DCache and write buffer configuration ................................................................... 4-11
Clock selection for external memory accesses ......................................................... 5-4
Relationship between bidirectional and unidirectional ASB interface ....................... 6-3
ARM920T input/output timing ................................................................................... 6-4
AMBA ASB transfer types ......................................................................................... 6-6
Burst transfers .......................................................................................................... 6-7
Use of WRITEOUT signal ......................................................................................... 6-8
Noncached LDR and fetch ...................................................................................... 6-12
Data eviction of 4 or 8 words .................................................................................. 6-18
ARM920T supported bus access types .................................................................. 6-23
Handshake encoding ................................................................................................ 7-8
Public instructions ................................................................................................... 9-14
ID code register ...................................................................................................... 9-20
Scan chain number allocation ................................................................................. 9-23
Scan chain 0 bit order ............................................................................................. 9-24
Scan chain 1 bit function ......................................................................................... 9-28
Scan chain 2 bit function ......................................................................................... 9-29
Scan chain 15 format and access modes ............................................................... 9-32
Scan chain 15 physical access mode bit format ..................................................... 9-33
Physical access mapping to CP15 registers ........................................................... 9-33
Scan chain 15 interpreted access mode bit format ................................................. 9-34
Interpreted access mapping to CP15 registers ....................................................... 9-35
Interpreted access mapping to the MMU ................................................................ 9-36
Interpreted access mapping to the caches ............................................................. 9-36
Scan chain 4 format ................................................................................................ 9-39
ARM9TDMI EmbeddedICE macrocell register map ............................................... 9-54
Watchpoint control register, data comparison bit functions .................................... 9-57
Watchpoint control register for instruction comparison bit functions ....................... 9-59
Debug status register bit functions ......................................................................... 9-60
Debug comms control register bit functions ............................................................ 9-65
ARM920T in TrackingICE mode ............................................................................. 10-4
AMBA test modes ................................................................................................... 11-3
AMBA functional test locations ............................................................................... 11-4
Construction of A920Inputs location ....................................................................... 11-5
Construction of A920Status1 location ..................................................................... 11-6
Construction of A920Status2 location ..................................................................... 11-7
Burst locations ...................................................................................................... 11-11
PA TAG RAM locations ........................................................................................ 11-12
Construction of data pattern write data ................................................................. 11-12
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
List of Tables
Table 11-9
Table 11-10
Table 11-11
Table 11-12
Table 11-13
Table 11-14
Table 11-15
Table 11-16
Table 11-17
Table 11-18
Table 11-19
Table 11-20
Table 11-21
Table 11-22
Table 11-23
Table 12-1
Table 12-2
Table 12-3
Table 13-1
Table 13-2
Table A-1
Table A-2
Table A-3
Table A-4
Table A-5
Table A-6
Table B-1
Table B-2
Table B-3
Table B-4
Table B-5
Table B-6
Table B-7
Table B-8
Table B-9
Table B-10
Table B-11
Table B-12
Table B-13
Table B-14
Table B-15
Table B-16
Table B-17
Table B-18
Table B-19
Table B-20
Table B-21
ARM DDI 0151C
Cache test locations .............................................................................................. 11-15
CAM write data ...................................................................................................... 11-15
CAM match write data ........................................................................................... 11-16
CAM match read data ........................................................................................... 11-16
Invalidate by VA write data .................................................................................... 11-16
Lockdown victim and base data ............................................................................ 11-17
MMU test locations ................................................................................................ 11-19
Invalidate by VA data ............................................................................................ 11-19
Match write data .................................................................................................... 11-20
CAM data .............................................................................................................. 11-20
CAM data Size_C encoding .................................................................................. 11-20
RAM1 data ............................................................................................................ 11-21
RAM1 data access permission bits ....................................................................... 11-21
RAM2 data ............................................................................................................ 11-22
RAM2 data Size_R2 encoding .............................................................................. 11-22
Symbols used in tables ........................................................................................... 12-3
Instruction cycle bus times ...................................................................................... 12-3
Data bus instruction times ....................................................................................... 12-4
ARM920T timing parameters ................................................................................ 13-16
ARM920T Trace Interface Port timing definitions ................................................. 13-26
AMBA signals ............................................................................................................ A-2
Coprocessor interface signals ................................................................................... A-5
JTAG and TAP controller signals .............................................................................. A-7
Debug signals ......................................................................................................... A-10
Miscellaneous signals ............................................................................................. A-12
Trace signals ........................................................................................................... A-13
Test state register ..................................................................................................... B-3
Clocking mode selection ........................................................................................... B-5
Register 7 operations ................................................................................................ B-8
Register 9 operations ................................................................................................ B-8
Register 15 operations .............................................................................................. B-9
CP15 MCR and MRC instructions ............................................................................. B-9
Register 7, 9, and 15 operations ............................................................................. B-10
Write cache victim and lockdown operations .......................................................... B-14
TTB register operations ........................................................................................... B-18
DAC register operations .......................................................................................... B-19
FSR register operations .......................................................................................... B-19
FAR register operations .......................................................................................... B-20
Register 8 operations .............................................................................................. B-20
Register 10 operations ............................................................................................ B-20
CAM, RAM1, and RAM2 register 15 operations ..................................................... B-20
Register 2, 3, 5, 6, 8, 10, and 15 operations ........................................................... B-21
CAM memory region size ........................................................................................ B-24
Access permission bit setting .................................................................................. B-25
Miss and fault encoding .......................................................................................... B-25
RAM2 memory region size ...................................................................................... B-26
Write TLB lockdown operations .............................................................................. B-27
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ix
List of Tables
x
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
List of Figures
ARM920T Technical Reference Manual
Figure P-1
Figure 1-1
Figure 2-1
Figure 2-2
Figure 2-3
Figure 2-4
Figure 2-5
Figure 2-6
Figure 2-7
Figure 2-8
Figure 2-9
Figure 2-10
Figure 3-1
Figure 3-2
Figure 3-3
Figure 3-4
Figure 3-5
Figure 3-6
Figure 3-7
Figure 3-8
Figure 3-9
Figure 3-10
Figure 3-11
ARM DDI 0151C
Key to timing diagram conventions ............................................................................ xix
ARM920T functional block diagram .......................................................................... 1-3
CP15 MRC and MCR bit pattern ............................................................................... 2-7
Cache type register format ........................................................................................ 2-9
Dsize and Isize field format ....................................................................................... 2-9
Register 7 MVA format ............................................................................................ 2-19
Register 7 index format ........................................................................................... 2-19
Register 8 MVA format ............................................................................................ 2-20
Register 9 ................................................................................................................ 2-22
Register 10 .............................................................................................................. 2-23
Register 13 .............................................................................................................. 2-24
Address mapping using CP15 Register 13 ............................................................. 2-25
Translation table base register .................................................................................. 3-6
Translating page tables ............................................................................................. 3-7
Accessing translation table level one descriptors ..................................................... 3-8
Level one descriptor .................................................................................................. 3-9
Section descriptor ................................................................................................... 3-10
Coarse page table descriptor .................................................................................. 3-11
Fine page table descriptor ....................................................................................... 3-12
Section translation ................................................................................................... 3-14
Level two descriptor ................................................................................................ 3-15
Large page translation from a coarse page table .................................................... 3-17
Small page translation from a coarse page table .................................................... 3-18
Copyright © 2000, 2001 ARM Limited. All rights reserved.
xi
List of Figures
Figure 3-12
Figure 3-13
Figure 3-14
Figure 4-1
Figure 5-1
Figure 5-2
Figure 5-3
Figure 5-4
Figure 5-5
Figure 6-1
Figure 6-2
Figure 6-3
Figure 6-4
Figure 6-5
Figure 6-6
Figure 6-7
Figure 6-8
Figure 6-9
Figure 6-10
Figure 7-1
Figure 7-2
Figure 7-3
Figure 7-4
Figure 7-5
Figure 7-6
Figure 7-7
Figure 9-1
Figure 9-2
Figure 9-3
Figure 9-4
Figure 9-5
Figure 9-6
Figure 9-7
Figure 9-8
Figure 9-9
Figure 9-10
Figure 9-11
Figure 9-12
Figure 9-13
Figure 9-14
Figure 9-15
Figure 9-16
Figure 9-17
Figure 10-1
Figure 11-1
Figure 11-2
Figure 12-1
xii
Tiny page translation from a fine page table ........................................................... 3-19
Domain access control register format ................................................................... 3-23
Sequence for checking faults .................................................................................. 3-25
Addressing the 16KB ICache .................................................................................... 4-5
ARM920T clocking .................................................................................................... 5-2
Synchronous mode FCLK to BCLK zero phase delay .............................................. 5-5
Synchronous mode FCLK to BCLK one phase delay ............................................... 5-5
Asynchronous mode FCLK to BCLK zero cycle delay .............................................. 5-6
Asynchronous mode FCLK to BCLK one cycle delay ............................................... 5-7
Output buffer for bidirectional signals ....................................................................... 6-5
Output buffer for unidirectional signals ..................................................................... 6-6
Instruction fetch after reset ..................................................................................... 6-11
Example LDR from address 0x108 ......................................................................... 6-12
Example LDM of 5 words from 0x108 ..................................................................... 6-13
Example nonbuffered STR ..................................................................................... 6-14
Example nonbuffered STM ..................................................................................... 6-15
Example linefill from 0x100 ..................................................................................... 6-16
Example 4-word data eviction ................................................................................. 6-17
Example swap operation ........................................................................................ 6-19
ARM920T coprocessor clocking ............................................................................... 7-3
ARM920T LDC/STC cycle timing ............................................................................. 7-5
ARM920T MCR/MRC transfer timing ....................................................................... 7-9
ARM920T interlocked MCR .................................................................................... 7-12
ARM920T late canceled CDP ................................................................................. 7-14
ARM920T privileged instructions ............................................................................ 7-15
ARM920T busy waiting and interrupts .................................................................... 7-18
Typical debug system ............................................................................................... 9-3
Breakpoint timing ...................................................................................................... 9-5
Watchpoint entry with data processing instruction .................................................... 9-8
Watchpoint entry with branch ................................................................................... 9-9
Test access port (TAP) controller state transitions ................................................. 9-12
External scan chain multiplexor .............................................................................. 9-22
Write back physical address format ........................................................................ 9-40
Clock switching on entry to debug state ................................................................. 9-43
Debug exit sequence .............................................................................................. 9-49
Debug state entry ................................................................................................... 9-50
ARM9TDMI EmbeddedICE macrocell overview ..................................................... 9-56
Watchpoint control register for data comparison .................................................... 9-57
Watchpoint control register for instruction comparison ........................................... 9-58
Debug control register ............................................................................................ 9-60
Debug status register .............................................................................................. 9-60
Vector catch register ............................................................................................... 9-61
Debug comms control register ................................................................................ 9-64
Using TrackingICE .................................................................................................. 10-2
AMBA functional test state machine ....................................................................... 11-9
Write data format .................................................................................................. 11-13
Single load interlock timing ..................................................................................... 12-6
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
List of Figures
Figure 12-2
Figure 12-3
Figure 12-4
Figure 13-1
Figure 13-2
Figure 13-3
Figure 13-4
Figure 13-5
Figure 13-6
Figure 13-7
Figure 13-8
Figure 13-9
Figure 13-10
Figure 13-11
Figure 13-12
Figure 13-13
Figure 13-14
Figure 13-15
Figure 13-16
Figure 13-17
Figure 13-18
Figure 13-19
Figure B-1
Figure B-2
Figure B-3
Figure B-4
Figure B-5
Figure B-6
Figure B-7
Figure B-8
Figure B-9
Figure B-10
Figure B-11
Figure B-12
Figure B-13
Figure B-14
Figure B-15
Figure B-16
ARM DDI 0151C
Two cycle load interlock .......................................................................................... 12-7
LDM interlock .......................................................................................................... 12-8
LDM dependent interlock ...................................................................................... 12-10
ARM920T FCLK timed coprocessor interface ......................................................... 13-2
ARM920T BCLK timed coprocessor interface ........................................................ 13-3
ARM920T FCLK related signal timing ..................................................................... 13-4
ARM920T BCLK related signal timing ..................................................................... 13-5
ARM920T SDOUTBS to TDO relationship .............................................................. 13-5
ARM920T nTRST to other signals relationship ....................................................... 13-6
ARM920T JTAG output signal timing ...................................................................... 13-7
ARM920T JTAG input signal timing ........................................................................ 13-8
ARM920T FCLK related debug output timing ......................................................... 13-8
ARM920T BCLK related debug output timing ......................................................... 13-9
ARM920T TCK related debug output timing ......................................................... 13-10
ARM920T EDBGRQ to DBGRQI relationship ....................................................... 13-10
ARM920T DBGEN to output relationship .............................................................. 13-11
ARM920T BCLK related Trace Interface Port timing ............................................ 13-11
ARM920T FCLK related Trace Interface Port timing ............................................. 13-12
ARM920T BnRES timing ....................................................................................... 13-12
ARM920T ASB slave transfer timing ..................................................................... 13-13
ARM920T ASB master transfer timing .................................................................. 13-14
ARM920T ASB master transfer timing .................................................................. 13-15
CP15 MRC and MCR bit pattern ............................................................................... B-2
Rd format, CAM read .............................................................................................. B-12
Rd format, CAM write .............................................................................................. B-12
Rd format, RAM read .............................................................................................. B-12
Rd format, RAM write .............................................................................................. B-13
Rd format, CAM match RAM read .......................................................................... B-13
Data format, CAM read ........................................................................................... B-13
Data format, RAM read ........................................................................................... B-13
Data format, CAM match RAM read ....................................................................... B-14
Rd format, write I or D cache victim and lockdown base ......................................... B-15
Rd format, write I or D cache victim ........................................................................ B-15
Rd format, CAM write and data format, CAM read .................................................. B-24
Rd format, RAM1 write ............................................................................................ B-24
Data format, RAM1 read ......................................................................................... B-25
Rd format, RAM2 write and data format, RAM2 read .............................................. B-26
Rd format, write I or D TLB lockdown ..................................................................... B-27
Copyright © 2000, 2001 ARM Limited. All rights reserved.
xiii
List of Figures
xiv
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Preface
This preface introduces the ARM920T processor and its reference documentation. It
contains the following sections:
•
About this document on page xvi
•
Further reading on page xx
•
Feedback on page xxi.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
xv
Preface
About this document
This document is the technical reference manual for the ARM920T processor.
Intended audience
This document has been written for hardware and software engineers who want to
design or develop products based upon the ARM920T processor. It assumes no prior
knowledge of ARM products.
Using this manual
This document is organized into the following chapters:
Chapter 1 Introduction
Read this chapter for an introduction to the ARM920T.
Chapter 2 Programmer’s Model
Read this chapter for a description of the programmer’s model for the
ARM920T.
Chapter 3 Memory Management Unit
Read this chapter for a description of the memory management unit and
the memory interface, including descriptions of the instruction and data
interfaces.
Chapter 4 Caches, Write Buffer, and Physical Address TAG (PA TAG) RAM
Read this chapter for descriptions of cache, write buffer, and PA TAG
RAM operation.
Chapter 5 Clock Modes
Read this chapter for a description of the processor clock modes.
Chapter 6 Bus Interface Unit
Read this chapter for a description of the bus interface unit and the
AMBA ASB and AHB interface.
Chapter 7 Coprocessor Interface
Read this chapter for a description of the ARM920T coprocessor
interface.
xvi
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Preface
Chapter 8 Trace Interface Port
Read this chapter for a description of the Trace Interface Port of the
ARM920T.
Chapter 9 Debug Support
Read this chapter for a description of the debug interface.
Chapter 10 TrackingICE
Read this chapter for a description of how the ARM920T uses
TrackingICE mode.
Chapter 11 AMBA Test Interface
Read this chapter for a description of the AMBA test interface.
Chapter 12 Instruction Cycle Summary and Interlocks
Read this chapter for details of instruction cycle times. This chapter
contains timing diagrams for interlock timing.
Chapter 13 AC Characteristics
Read this chapter for a description of the timing parameters used in the
ARM920T.
Appendix A Signal Descriptions
Read this chapter for a detailed description of the signals used in the
ARM920T.
Appendix B CP15 Test Registers
Read this chapter for a detailed description of the CP15 test register used
in the ARM920T.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
xvii
Preface
Typographical conventions
The following typographical conventions are used in this book:
bold
Highlights ARM processor signal names, and interface elements, such as
menu names and buttons. Also used for terms in descriptive lists, where
appropriate.
italic
Highlights special terminology, cross-references, and citations.
typewriter
Denotes text that can be entered at the keyboard, such as commands, file
and program names, and source code.
typewriter
Denotes a permitted abbreviation for a command or option. The
underlined text may be entered instead of the full command or option
name.
typewriter italic
Denotes arguments to commands or functions, where the argument is to
be replaced by a specific value.
typewriter bold
Denotes language keywords when used outside example code.
xviii
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Preface
Timing diagram conventions
This manual contains a number of timing diagrams. Figure P-1 explains the components
used in these diagrams. Any variations are clearly labeled when they occur. Therefore,
you must not attach any additional meaning unless specifically stated.
Clock
HIGH to LOW
Transient
HIGH/LOW to HIGH
Bus stable
Bus to high impedance
Bus change
High impedance to stable bus
Figure P-1 Key to timing diagram conventions
Shaded bus and signal areas are undefined, so the bus or signal can assume any value
within the shaded area at that time. The actual level is unimportant and does not affect
normal operation.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
xix
Preface
Further reading
This section lists publications by ARM Limited, and by third parties.
If you would like further information on ARM products, or if you have questions not
answered by this document, please contact [email protected] or visit our web site at
http://www.arm.com.
ARM publications
This document contains information that is specific to the ARM920T processor. Refer
to the following documents for other relevant information:
•
ARM Architecture Reference Manual (ARM DDI 0100)
•
ARM9TDMI Data Sheet (ARM DDI 0029).
Other publications
This section lists relevant documents published by third parties.
•
IEEE Std. 1149.1- 1990, Standard Test Access Port and Boundary-Scan
Architecture.
xx
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Preface
Feedback
ARM Limited welcomes feedback both on the ARM920T processor, and on the
documentation.
Feedback on the ARM920T
If you have any comments or suggestions about this product, please contact your
supplier giving:
•
the product name
•
a concise explanation of your comments.
Feedback on the ARM920T Technical Reference Manual
If you have any comments about this document, please send email to [email protected]
giving:
•
the document title
•
the document number
•
the page number(s) to which your comments refer
•
a concise explanation of your comments.
General suggestions for additions and improvements are also welcome.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
xxi
Preface
xxii
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Chapter 1
Introduction
This chapter introduces the ARM920T processor. It contains the following sections:
•
About the ARM920T on page 1-2
•
Processor functional block diagram on page 1-3.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
1-1
Introduction
1.1
About the ARM920T
The ARM920T processor is a member of the ARM9TDMI family of general-purpose
microprocessors, which includes:
•
ARM9TDMI (core)
•
ARM940T (core plus cache and protection unit)
•
ARM920T (core plus cache and MMU).
The ARM9TDMI processor core is a Harvard architecture device implemented using a
five-stage pipeline consisting of Fetch, Decode, Execute, Memory, and Write stages. It
can be provided as a standalone core that can be embedded into more complex devices.
The standalone core has a simple bus interface that allows you to design your own
caches and memory systems around it.
The ARM9TDMI family of microprocessors supports both the 32-bit ARM and 16-bit
Thumb instruction sets, allowing you to trade off between high performance and high
code density.
The ARM920T processor is a Harvard cache architecture processor that is targeted at
multiprogrammer applications where full memory management, high performance, and
low power are all-important. The separate instruction and data caches in this design are
16KB each in size, with an 8-word line length. The ARM920T processor implements
an enhanced ARM architecture v4 MMU to provide translation and access permission
checks for instruction and data addresses.
The ARM920T processor supports the ARM debug architecture and includes logic to
assist in both hardware and software debug. The ARM920T processor also includes
support for coprocessors, exporting the instruction and data buses along with simple
handshaking signals.
The ARM920T interface to the rest of the system is over unified address and data buses.
This interface enables implementation of either an Advanced Microcontroller Bus
Architecture (AMBA) Advanced System Bus (ASB) or Advanced High-performance
Bus (AHB) bus scheme either as a fully-compliant AMBA bus master, or as a slave for
production test. The ARM920T processor also has a Tracking ICE mode which allows
an approach similar to a conventional ICE mode of operation.
The ARM920T processor supports the addition of an Embedded Trace Macrocell
(ETM) for real-time tracing of instructions and data.
1-2
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Introduction
1.2
Processor functional block diagram
Figure 1-1 shows the functional block diagram of the ARM920T processor.
External
coprocessor
interface
Instruction
cache
IPA[31:0]
Instruction
MMU
IMVA[31:0]
R13
ID[31:0]
IVA[31:0]
ARM9TDMI
Processor core
(Integral EmbeddedICE)
Trace
interface
port
DVA[31:0]
AMBA
bus
interface
CP15
DD[31:0]
ASB
Write
buffer
R13
DMVA[31:0]
JTAG
Data
cache
DPA[31:0]
Data
MMU
Write back
PA TAG RAM
WBPA[31:0]
DINDEX[5:0]
Figure 1-1 ARM920T functional block diagram
The blocks shown in Figure 1-1 are described as follows:
ARM DDI 0151C
•
The ARM9TDMI core is described in the ARM9TDMI Technical Reference
Manual.
•
Register 13 and coprocessor 15 are described in Chapter 2 Programmer’s Model.
•
The instruction and data MMUs are described in Chapter 3 Memory Management
Unit.
•
The instruction and data caches, the write buffer, and the write-back PA TAG
RAM are described in Chapter 4 Caches, Write Buffer, and Physical Address TAG
(PA TAG) RAM.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
1-3
Introduction
1-4
•
The AMBA bus interface is described in Chapter 6 Bus Interface Unit.
•
The external coprocessor interface is described in Chapter 7 Coprocessor
Interface.
•
The trace interface port is described in Chapter 8 Trace Interface Port.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Chapter 2
Programmer’s Model
This chapter describes the ARM920T registers and provides details required when
programming the microprocessor. It contains the following sections:
•
About the programmer’s model on page 2-2
•
About the ARM9TDMI programmer’s model on page 2-3
•
CP15 register map summary on page 2-5.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
2-1
Programmer’s Model
2.1
About the programmer’s model
The ARM920T processor incorporates the ARM9TDMI integer core, which
implements the ARM architecture v4T. It executes the ARM and Thumb instruction
sets, and includes EmbeddedICE JTAG software debug features.
The programmer’s model of the ARM920T processor consists of the programmer’s
model of the ARM9TDMI core (see About the ARM9TDMI programmer’s model on
page 2-3) with the following additions and modifications:
•
2-2
The ARM920T processor incorporates two coprocessors:
—
CP14, which allows software access to the debug communications channel.
You can access the registers defined in CP14 using MCR and MRC instructions.
These are described in Debug communications channel on page 9-64.
—
The system control coprocessor, CP15, which provides additional registers
that are used to configure and control the caches, MMU, protection system,
the clocking mode, and other system options of the ARM920T, such as big
or little-endian operation. You can access the registers defined in CP15
using MCR and MRC instructions. These are described in CP15 register map
summary on page 2-5.
•
The ARM920T processor also features an external coprocessor interface that
allows the attachment of a closely-coupled coprocessor on the same chip, for
example, a floating-point unit. You can access registers and operations provided
by any coprocessors attached to the external coprocessor interface using
appropriate coprocessor instructions.
•
Memory accesses for instruction fetches and data loads and stores can be cached
or buffered. Cache and write buffer configuration and operation is described in
detail in Chapter 4 Caches, Write Buffer, and Physical Address TAG (PA TAG)
RAM.
•
The MMU page tables that reside in main memory describe the virtual to physical
address mapping, access permissions, and cache and write buffer configuration.
These are created by the operating system software and accessed automatically by
the ARM920T MMU hardware whenever an access causes a TLB miss.
•
The ARM920T has a Trace Interface Port that allows the use of Trace hardware
and tools for real-time tracing of instructions and data.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Programmer’s Model
2.2
About the ARM9TDMI programmer’s model
The ARM9TDMI processor core implements ARM architecture v4T, and executes the
ARM 32-bit instruction set and the compressed Thumb 16-bit instruction set. The
programmer’s model is fully described in the ARM Architecture Reference Manual. The
ARM9TDMI Technical Reference Manual gives implementation details, including
instruction execution cycle times.
ARMv4T specifies a small number of implementation options. The options selected in
the ARM9TDMI implementation are listed in Table 2-1. For comparison, the options
selected for the ARM7TDMI implementation are also shown.
Table 2-1 ARM9TDMI implementation options
Processor
core
Architecture
Data Abort
model
Value stored by direct STR,
STRT, and STM of PC
ARM7TDMI
ARMv4T
Base updated
Address of instruction + 12
ARM9TDMI
ARMv4T
Base restored
Address of instruction + 12
The ARM9TDMI is code-compatible with the ARM7TDMI, with two exceptions:
•
The ARM9TDMI core implements the base restored Data Abort model. This
significantly simplifies the software Data Abort handler.
•
The ARM9TDMI fully implements the instruction set extension spaces added to
the ARM (32-bit) instruction set in ARMv4 and ARMv4T.
These differences are explained in more detail in the following sections:
•
Data Abort model on page 2-3
•
Instruction set extension spaces on page 2-4.
2.2.1
Data Abort model
The base restored Data Abort model differs from the base updated Data Abort model
implemented by ARM7TDMI.
The difference in the Data Abort models affects only a very small section of operating
system code, the Data Abort handler. It does not affect user code. With the base restored
Data Abort model, when a Data Abort exception occurs during the execution of a
memory access instruction, the base register is always restored by the processor
hardware to the value the register contained before the instruction was executed. This
removes the requirement for the Data Abort handler to unwind any base register update
that might have been specified by the aborted instruction.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
2-3
Programmer’s Model
2.2.2
Instruction set extension spaces
All ARM processors implement the undefined instruction space as one of the entry
mechanisms for the undefined instruction exception. That is, ARM instructions with
opcode[27:25] = 0b011 and opcode[4] = 0b1 are undefined on all ARM processors
including the ARM9TDMI and ARM7TDMI.
ARMv4 and ARMv4T also introduce a number of instruction set extension spaces to
the ARM instruction set. These are:
•
arithmetic instruction extension space
•
control instruction extension space
•
coprocessor instruction extension space
•
load/store instruction extension space.
Instructions in these spaces are undefined, and cause an undefined instruction
exception. The ARM9TDMI core fully implements all the instruction set extension
spaces defined in ARMv4T as undefined instructions, allowing emulation of future
instruction set additions.
2-4
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Programmer’s Model
2.3
CP15 register map summary
CP15 defines 16 registers. The register map for CP15 is shown in Table 2-2.
Table 2-2 CP15 register map
Register
Read
Write
0
ID code a
Unpredictable
0
Cache type a
Unpredictable
1
Control
Control
2
Translation table base
Translation table base
3
Domain access control
Domain access control
4
Unpredictable
Unpredictable
5
Fault status b
Fault status b
6
Fault address
Fault address
7
Unpredictable
Cache operations
8
Unpredictable
TLB operations
9
Cache lockdown b
Cache lockdown b
10
TLB lockdown b
TLB lockdown b
11
Unpredictable
Unpredictable
12
Unpredictable
Unpredictable
13
FCSE PID
FCSE PID
14
Unpredictable
Unpredictable
15
Test configuration
Test configuration
a. Register location 0 provides access to more than one
register. The register accessed depends on the value of the
opcode_2 field. See the register description for details.
b. Separate registers for instruction and data. See the register
description for details.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
2-5
Programmer’s Model
2.3.1
Addresses in ARM920T
Three distinct types of address exist in an ARM920T system:
•
Virtual Address (VA)
•
Modified Virtual Address (MVA)
•
Physical Address (PA).
Below is an example of the address manipulation when the ARM9TDMI core requests
an instruction (see Figure 2-10 on page 2-25).
1.
The Instruction VA (IVA) is issued by the ARM9TDMI core.
2.
This is translated by the ProcID to the Instruction MVA (IMVA). It is the IMVA
that the Instruction Cache (ICache) and MMU see.
3.
If the protection check carried out by the IMMU on the IMVA does not abort, and
the IMVA tag is in the ICache, the instruction data is returned to the ARM9TDMI
core.
4.
If the ICache misses (the IMVA tag is not in the ICache), then the IMMU
performs a translation to produce the Instruction PA (IPA). This address is given
to the AMBA bus interface to perform an external access.
Table 2-3 Address types in ARM920T
2.3.2
Domain
ARM9TDMI
Caches and TLBs
AMBA bus
Address
Virtual (VA)
Modified Virtual (MVA)
Physical (PA)
Accessing CP15 registers
The terms and abbreviations shown in Table 2-4 are used throughout this section.
Table 2-4 CP15 abbreviations
2-6
Term
Abbreviation
Description
Unpredictable
UNP
For reads, the data returned when reading from this
location is unpredictable. It can have any value.
For writes, writing to this location causes unpredictable
behavior, or an unpredictable change in device
configuration.
Should be zero
SBZ
When writing to this location, all bits of this field should
be 0.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Programmer’s Model
In all cases, reading from, or writing any data values to any CP15 registers, including
those fields specified as unpredictable or should be zero, does not cause any permanent
damage.
All CP15 register bits that are defined and contain state, are set to zero by BnRES
except the V bit in register 1, which takes the value of macrocell input VINITHI when
BnRES is asserted.
You can only access CP15 registers with MRC and MCR instructions in a privileged mode.
The instruction bit pattern of the MCR and MRC instructions is shown in Figure 2-1. The
assembler for these instructions is:
MCR/MRC{cond} P15,opcode_1,Rd,CRn,CRm,opcode_2
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
1 1 1 0
Cond
1 1 1 1
opcode_1
CRn
Rd
1
opcode_2
CRm
L
Figure 2-1 CP15 MRC and MCR bit pattern
Instructions CDP, LDC, and STC, together with unprivileged MRC and MCR instructions to
CP15, cause the undefined instruction trap to be taken. The CRn field of MRC and MCR
instructions specifies the coprocessor register to access. The CRm field and opcode_2
fields specify a particular action when addressing registers. The L bit distinguishes
between an MRC (L=1) and an MCR (L=0).
Note
Attempting to read from a nonreadable register, or to write to a nonwritable register
causes unpredictable results.
The opcode_1, opcode_2, and CRm fields should be zero, except when the values specified
are used to select the desired operations, in all instructions that access CP15. Using
other values results in unpredictable behavior.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
2-7
Programmer’s Model
2.3.3
Register 0, ID code register
This is a read-only register that returns a 32-bit device ID code.
You can access the ID code register by reading CP15 register 0 with the opcode_2 field
set to any value other than 1 (the CRm field should be zero when reading). For example:
MRC p15,0,Rd,c0,c0,0
; returns ID register
The contents of the ID code are shown in Table 2-5.
Table 2-5 Register 0, ID code
2.3.4
Register bits
Function
Value
31:24
Implementer
0x41
23:20
Specification revision
0x1
19:16
Architecture (ARMv4T)
0x2
15:4
Part number
0x920
3:0
Layout revision
Revision
Register 0, cache type register
This is a read-only register that contains information about the size and architecture of
the caches, allowing operating systems to establish how to perform such operations as
cache cleaning and lockdown. All ARMv4T and later cached processors contain this
register, allowing RTOS vendors to produce future-proof versions of their operating
systems.
You can access the cache type register by reading CP15 register 0 with the opcode_2 field
set to 1. For example:
MRC p15,0,Rd,c0,c0,1
2-8
; returns cache details
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Programmer’s Model
The format of the cache type register is shown in Figure 2-2.
31 30 29 28
0 0 0
25 24 23
ctype
S
12 11
0
Dsize
Isize
Figure 2-2 Cache type register format
ctype
The ctype field determines the cache type.
S bit
Specifies whether the cache is a unified cache or separate instruction and
data caches.
Dsize
Specifies the size, line length, and associativity of the data cache.
Isize
Specifies the size, line length, and associativity of the instruction cache.
The Dsize and Isize fields in the cache type register have the same format. This is shown
in Figure 2-3.
11 10 9 8 7 6 5 4 3 2 1 0
0 0 0
size
assoc
M len
23 22 21 20 19 18 17 16 15 14 13 12
Figure 2-3 Dsize and Isize field format
ARM DDI 0151C
size
The size field determines the cache size in conjunction with the M bit.
assoc
The assoc field determines the cache associativity in conjunction with the
M bit.
M bit
The multiplier bit. Determines the cache size and cache associativity
values in conjunction with the size and assoc fields.
len
The len field determines the line length of the cache.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
2-9
Programmer’s Model
The register values for the ARM920T cache type register are listed in Table 2-6.
Table 2-6 Cache type register format
Function
Register bits
Value
Reserved
31:29
0b000
ctype
28:25
0b0110
S
24
0b1 = Harvard cache
Reserved
23:21
0b000
size
20:18
0b101 = 16KB
assoc
17:15
0b110 = 64-way
M
14
0b0
len
13:12
0b10 = 8 words per line (32 bytes)
Reserved
11:9
0b000
size
8:6
0b101 = 16KB
assoc
5:3
0b110 = 64-way
M
2
0b0
len
1:0
0b10 = 8 words per line (32 bytes)
Dsize
Isize
Bits [28:25] indicate which major cache class the implementation falls into. 0x6 means
that the cache provides:
•
cache-clean-step operation
•
cache-flush-step operation
•
lockdown facilities.
2-10
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Programmer’s Model
The size of the cache is determined by the size field and the M bit. The M bit is 0 for
the data and instruction caches. Bits [20:18] for the Data Cache (DCache) and bits [8:6]
for the Instruction Cache (ICache) are the size field. Table 2-7 shows the cache size
encoding.
Table 2-7 Cache size encoding (M=0)
size field
Cache size
0b000
512B
0b001
1KB
0b010
2KB
0b011
4KB
0b100
8KB
0b101
16KB
0b110
32KB
0b111
64KB
The associativity of the cache is determined by the assoc field and the M bit. The M bit
is 0 for the data and instruction caches. Bits [17:15] for the DCache and bits [5:3] for
the ICache are the assoc field. Table 2-8 shows the cache associativity encoding.
Table 2-8 Cache associativity encoding (M=0)
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
assoc field
Associativity
0b000
Direct mapped
0b001
2-way
0b010
4-way
0b011
8-way
0b100
16-way
0b101
32-way
0b110
64-way
0b111
128-way
2-11
Programmer’s Model
The line length of the cache is determined by the len field. Bits [13:12] for the DCache
and bits [1:0] for the ICache are the len field. Table 2-9 shows the line length encoding.
Table 2-9 Line length encoding
2.3.5
len field
Cache line length
00
2 words (8 bytes)
01
4 words (16 bytes)
10
8 words (32 bytes)
11
16 words (64 bytes)
Register 1, control register
This register contains the control bits of the ARM920T. All reserved bits must either be
written with 0 or 1, as indicated, or written using read-modify-write. The reserved bits
have an unpredictable value when read. Use the following instructions to read and write
this register:
MRC p15, 0, Rd, c1, c0, 0
MCR p15, 0, Rd, c1, c0, 0
; read control register
; write control register
All defined control bits are set to 0 on reset, except the V bit. The V bit is set to 0 at reset
if the VINITHI pin is LOW, or 1 if the VINITHI pin is HIGH. The functions of the
control bits are shown in Table 2-10.
Table 2-10 Control register 1 bit functions
2-12
Register
bits
Name
Function
Value
31
iA bit
Asynchronous clock select
See Table 2-11 on page 2-14.
30
nF bit
notFastBus select
See Table 2-11 on page 2-14.
29:15
-
Reserved
Read = Unpredictable.
Write = Should be zero.
14
RR bit
Round robin replacement
0 = Random replacement.
1 = Round-robin replacement.
13
V bit
Base location of exception
registers
0 = Low addresses = 0x00000000.
1 = High addresses = 0xFFFF0000.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Programmer’s Model
Table 2-10 Control register 1 bit functions (continued)
ARM DDI 0151C
Register
bits
Name
Function
Value
12
I bit
ICache enable
0 = ICache disabled.
1 = ICache enabled.
11:10
-
Reserved
Read = 00.
Write = 00.
9
R bit
ROM protection
This bit modifies the MMU protection
system. See Domain access control on
page 3-23.
8
S bit
System protection
This bit modifies the MMU protection
system. See Domain access control on
page 3-23.
7
B bit
Endianness
0 = Little-endian operation.
1 = Big-endian operation.
6:3
-
Reserved
Read = 1111.
Write = 1111.
2
C bit
DCache enable
0 = DCache disabled.
1 = DCache enabled.
1
A bit
Alignment fault enable
Data address alignment fault checking.
0 = Fault checking disabled.
1 = Fault checking enabled.
0
M bit
MMU enable
0 = MMU disabled.
1 = MMU enabled.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
2-13
Programmer’s Model
Register 1 bits [31:30] select the clocking mode of the ARM920T, as shown in
Table 2-11.
Table 2-11 Clocking modes
Clocking mode
iA
nF
FastBus mode
0
0
Synchronous
0
1
Reserved
1
0
Asynchronous
1
1
Enabling the MMU
You must take care with the address mapping of the code sequence used to enable the
MMU (see Enabling the MMU on page 3-29).
See Enabling and disabling the ICache on page 4-6 and Enabling and disabling the
DCache and write buffer on page 4-10 for the restrictions and the effects of having
caches enabled with the MMU disabled.
2.3.6
Register 2, translation table base (TTB) register
This is the Translation Table Base (TTB) register, for the currently active first-level
translation table. The contents of register 2 are shown in Table 2-12.
Table 2-12 Register 2, translation table base
Register
bits
Function
31:14
Pointer to first-level translation
table base. Read/write.
13:0
Reserved:
Read = Unpredictable.
Write = Should be zero.
Reading from register 2 returns the pointer to the currently active first-level translation
table in bits [31:14]. Writing to register 2 updates the pointer to the first-level translation
table from bits [31:14] of the written value.
Bits [13:0] should be zero when written, and are unpredictable when read.
2-14
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Programmer’s Model
You can use the following instructions to access the TTB:
MRC p15, 0, Rd, c2, c0, 0
MCR p15, 0, Rd, c2, c0, 0
2.3.7
; read TTB register
; write TTB register
Register 3, domain access control register
Register 3 is the read and write domain access control register, consisting of 16 2-bit
fields. Each of these 2-bit fields defines the access permissions for the domains shown
in Table 2-13.
Table 2-13 Register 3, domain access control
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
Register
bits
Domain
31:30
D15
29:28
D14
27:26
D13
25:24
D12
23:22
D11
21:20
D10
19:18
D9
17:16
D8
15:14
D7
13:12
D6
11:10
D5
9:8
D4
7:6
D3
5:4
D2
3:2
D1
1:0
D0
2-15
Programmer’s Model
The encoding of the two bit domain access permission field is given in Domain access
control on page 3-23. You can use the following instructions to access the domain
access control register:
MRC p15, 0, Rd, c3, c0, 0
MCR p15, 0, Rd, c3, c0, 0
2.3.8
; read domain 15:0 access permissions
; write domain 15:0 access permissions
Register 4, reserved
You must not access (read or write) this register because it causes unpredictable
behavior.
2.3.9
Register 5, fault status registers
Register 5 is the Fault Status Register (FSR). The FSR contains the source of the last
data fault, indicating the domain and type of access being attempted when the Data
Abort occurred. Table 2-14 shows bit allocations for the FSR.
Table 2-14 Fault status register
Bit
Description
31:9
UNP when read
SBZ for write
8
0 when read
SBZ for write
7:4
Domain being accessed when fault
occurred (D15 - D0)
3:0
Fault type
The fault type encoding is shown in Fault address and fault status registers on
page 3-22.
The data FSR is defined in ARMv4T. Additionally, a pipelined prefetch FSR is
available, for debug purposes only. The pipeline matches that of the ARM9TDMI.
You can use the following instructions to access the data and prefetch FSR:
MRC
MCR
MRC
MCR
2-16
p15,
p15,
p15,
p15,
0,
0,
0,
0,
Rd,
Rd,
Rd,
Rd,
c5,
c5,
c5,
c5,
c0,
c0,
c0,
c0,
0
0
1
1
;read data FSR value
;write data FSR value
;read prefetch FSR value
;write prefetch FSR value
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Programmer’s Model
The ability to write to the FSR is useful for a debugger to restore the value of the FSR.
You must write to the register using the read-modify-write method. Bits[31:8] should
be zero.
2.3.10
Register 6, fault address register
Register 6 is the Fault Address Register (FAR). This contains the MVA of the access
being attempted when the last fault occurred. The FAR is only updated for data faults,
not for prefetch faults. (You can find the address for a prefetch fault in R14.)
You can use the following instructions to access the FAR:
MRC p15, 0, Rd, c6, c0, 0
MCR p15, 0, Rd, c6, c0, 0
;read FAR data
;write FAR data
The ability to write to the FAR is provided to allow a debugger to restore a previous
state.
2.3.11
Register 7, cache operations register
Register 7 is a write-only register used to manage the ICache and DCache.
The cache operations provided by register 7 are described in Table 2-15.
Table 2-15 Function descriptions register 7
Function
Description
Invalidate cache
Invalidates all cache data, including any dirty data.a Use with
caution.
Invalidate single entry using
MVA
Invalidates a single cache line, discarding any dirty data.a Use
with caution.
Clean D single entry using
either index or MVA
Writes the specified cache line to main memory, if the line is
marked valid and dirty, and marks the line as not dirty.a The
valid bit is unchanged.
Clean and Invalidate D entry
using either index or MVA
Writes the specified cache line to main memory, if the line is
marked valid and dirty.a The line is marked not valid.
Prefetch cache line
Performs an ICache lookup of the specified MVA.
If the cache misses, and the region is cachable, a linefill is
performed.
a. Dirty data is data that has been modified in the cache but not yet written to main memory.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
2-17
Programmer’s Model
The function of each cache operation is selected by the opcode_2 and CRm fields in the
MCR instruction used to write CP15 register 7. Writing other opcode_2 or CRm values is
unpredictable.
Reading from CP15 register 7 is unpredictable.
Table 2-16 shows instructions that you can use to perform cache operations with
register 7.
Table 2-16 Cache operations register 7
Function
Data
Instruction
Invalidate ICache and DCache
SBZ
MCR p15,0,Rd,c7,c7,0
Invalidate ICache
SBZ
MCR p15,0,Rd,c7,c5,0
Invalidate ICache single entry (using MVA)
MVA
format
MCR p15,0,Rd,c7,c5,1
Prefetch ICache line (using MVA)
MVA
format
MCR p15,0,Rd,c7,c13,1
Invalidate DCache
SBZ
MCR p15,0,Rd,c7,c6,0
Invalidate DCache single entry (using
MVA)
MVA
format
MCR p15,0,Rd,c7,c6,1
Clean DCache single entry (using MVA)
MVA
format
MCR p15,0,Rd,c7,c10,1
Clean and Invalidate DCache entry (using
MVA)
MVA
format
MCR p15,0,Rd,c7,c14,1
Clean DCache single entry (using index)
Index
format
MCR p15,0,Rd,c7,c10,2
Clean and Invalidate DCache entry (using
index)
Index
format
MCR p15,0,Rd,c7,c14,2
Drain write buffer a
SBZ
MCR p15,0,Rd,c7,c10,4
Wait for interrupt b
SBZ
MCR p15,0,Rd,c7,c0,4
a. Stops execution until the write buffer has drained.
b. Stops execution in a LOW power state until an interrupt occurs.
2-18
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Programmer’s Model
The operations that you can carry out on a single cache line identify the line using the
data passed in the MCR instruction. The data is interpreted using one of the formats shown
in Figure 2-4 or Figure 2-5.
31
5 4
0
SBZ
Modified virtual address
Figure 2-4 Register 7 MVA format
31
26 25
Index
8 7
5 4
Seg
SBZ
0
SBZ
Figure 2-5 Register 7 index format
The use of register 7 is described in Chapter 4 Caches, Write Buffer, and Physical
Address TAG (PA TAG) RAM.
2.3.12
Register 8, TLB operations register
Register 8 is a write-only register used to manage the Translation Lookaside Buffers
(TLBs), the instruction TLB, and the data TLB.
Five TLB operations are defined and you can select the function to be performed with
the opcode_2 and CRm fields in the MCR instruction used to write CP15 register 8. Writing
other opcode_2 or CRm values is unpredictable. Reading from CP15 register 8 is
unpredictable.
Table 2-17 shows instructions that you can use to perform TLB operations using
register 8.
Table 2-17 TLB operations register 8
ARM DDI 0151C
Function
Data
Instruction
Invalidate TLB(s)
SBZ
MCR p15,0,Rd,c8,c7,0
Invalidate I TLB
SBZ
MCR p15,0,Rd,c8,c5,0
Copyright © 2000, 2001 ARM Limited. All rights reserved.
2-19
Programmer’s Model
Table 2-17 TLB operations register 8 (continued)
Function
Data
Instruction
Invalidate I TLB single entry (using MVA)
MVA
format
MCR p15,0,Rd,c8,c5,1
Invalidate D TLB
SBZ
MCR p15,0,Rd,c8,c6,0
Invalidate D TLB single entry (using MVA)
MVA
format
MCR p15,0,Rd,c8,c6,1
Note
These functions invalidate all the unpreserved entries in the TLB. Invalidate TLB single
entry functions invalidate any TLB entry corresponding to the MVA given in Rd,
regardless of its preserved state. See Register 10, TLB lockdown register on page 2-22.
Figure 2-6 shows the MVA format used for operations on single entry TLB lines using
register 8.
31
10 9
0
SBZ
Modified virtual address
Figure 2-6 Register 8 MVA format
2.3.13
Register 9, cache lockdown register
Register 9 is the cache lockdown register. The cache lockdown register is 0x0 on reset.
The cache lockdown register allows software to control which cache line in the ICache
or DCache respectively is loaded for a linefill and to prevent lines in the ICache or
DCache from being evicted during a linefill, locking them into the cache.
There is a register for each of the ICache and DCache. The value of opcode_2 determines
which cache register to access:
opcode_2 = 0x0 accesses the DCache register
•
•
opcode_2 = 0x1 accesses the ICache register.
The Opcode_1 and CRm fields should be zero.
Reading CP15 register 9 returns the value of the cache lockdown register, which is the
base pointer for all cache segments.
2-20
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Programmer’s Model
Note
Only bits [31:26] are returned. Bits [25:0] are unpredictable.
Writing CP15 register 9 updates the cache lockdown register, both the base and the
current victim pointer for all cache segments. Bits [25:0] should be zero.
The victim counter specifies the cache line to be used as the victim for the next linefill.
This is incremented using either a random or round-robin replacement policy,
determined by the state of the RR bit in register 1. The victim counter generates values
in the range (base to 63). This locks lines with index values in the range (0 to base-1).
If base = 0, there are no locked lines.
Writing to CP15 register 9 updates the base pointer and the current victim pointer. The
next linefill uses, and then increments, the victim pointer. The victim pointer continues
incrementing on linefills, and wraps around to the base pointer. For example, setting the
base pointer to 0x3 prevents the victim pointer from selecting entries 0x0 to 0x2, locking
them into the cache. Example 2-1 shows how you can load a cache line into ICache line
0 and lock it down.
Example 2-1 Load a cache line into ICache line 0 and lock it down
MCR to CP15 register 9, opcode_2 = 0x1, Victim=Base=0x0
MCR I prefetch. Assuming the ICache misses, a linefill occurs to line 0.
MCR to CP15 register 9, opcode_2 = 0x1, Victim=Base=0x1
More ICache linefills now occur into lines 1-63.
Example 2-2 shows how you can load a cache line into DCache line 0 and lock it down.
Example 2-2 Load a cache line into DCache line 0 and lock it down
MCR to CP15 register 9, opcode_2 = 0x0, Victim=Base=0x0
Data load (LDR/LDM). Assuming the DCache misses, a linefill occurs to line 0.
MCR to CP15 register 9, opcode_2 = 0x0, Victim=Base=0x1
More DCache linefills now occur into lines 1-63.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
2-21
Programmer’s Model
Note
Writing CP15 register 9, with the CRm field set to b0001, updates the current victim
pointer only for the specified segment. Bits [31:26] specify the victim. Bits [7:5] specify
the segment (for a 16KB cache). All other bits should be zero. This encoding is intended
for debug use. You are not recommended to use this encoding.
Figure 2-7 shows the format of bits in register 9.
31
26 25
0
Index
UNP/SBZ
Figure 2-7 Register 9
Table 2-18 shows the instructions you can use to access the cache lockdown register.
Table 2-18 Accessing the cache lockdown register 9
2.3.14
Function
Data
Instruction
Read DCache lockdown base
Base
MRC p15,0,Rd,c9,c0,0
Write DCache victim and lockdown base
Victim=Base
MCR p15,0,Rd,c9,c0,0
Read ICache lockdown base
Base
MRC p15,0,Rd,c9,c0,1
Write ICache victim and lockdown base
Victim=Base
MCR p15,0,Rd,c9,c0,1
Register 10, TLB lockdown register
Register 10 is the TLB lockdown register. The TLB lockdown register is 0x0 on reset.
There is a TLB lockdown register for each of the TLBs, the value of opcode_2
determines which TLB register to access:
opcode_2 = 0x0 accesses the D TLB register
•
•
opcode_2 = 0x1 accesses the I TLB register.
Reading CP15 register 10 returns the value of the TLB lockdown counter base register,
the current victim number, and the preserve bit (P bit). Bits [19:1] are unpredictable
when read.
Writing CP15 register 10 updates the TLB lockdown counter base register, the current
victim pointer, and the state of the preserve bit. Bits [19:1] should be zero when written.
2-22
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Programmer’s Model
Table 2-19 shows the instructions you can use to access the TLB lockdown register.
Table 2-19 Accessing the TLB lockdown register 10
Function
Data
Instruction
Read D TLB lockdown
TLB lockdown
MRC p15,0,Rd,c10,c0,0
Write D TLB lockdown
TLB lockdown
MCR p15,0,Rd,c10,c0,0
Read I TLB lockdown
TLB lockdown
MRC p15,0,Rd,c10,c0,1
Write I TLB lockdown
TLB lockdown
MCR p15,0,Rd,c10,c0,1
Figure 2-8 shows the format of bits in register 10.
31
26 25
Base
20 19
Victim
1 0
SBZ/UNP
P
Figure 2-8 Register 10
The entries in the TLBs are replaced using a round-robin replacement policy. This is
implemented using a victim counter that counts from entry 0 up to 63, and then wraps
back round to the base value and continues counting, wrapping around to the base value
from 63 each time.
There are two mechanisms available for ensuring entries are not removed from the TLB:
ARM DDI 0151C
•
Locking an entry down prevents it from being selected for overwriting during a
table walk. You can do this by programming the base value to which the victim
counter reloads. For example, if the bottom 3 entries (0–2) are to be locked down,
you must program the base counter to 3.
•
You can preserve an entry during an Invalidate All instruction. You can do this
by ensuring the P bit is set when the entry is loaded into the TLB. Examples that
show how you can load a single entry into the I and D TLBs at location 0, make
it immune to Invalidate All, and lock it down are shown in Example 2-3 on
page 2-24 and Example 2-4 on page 2-24.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
2-23
Programmer’s Model
Example 2-3 Load a single entry into I TLB location 0, make it immune to Invalidate
All and lock it down
MCR to CP15 register 10, opcode_2 = 0x1, Base Value = 0,
Current Victim = 0, P = 1
MCR I prefetch. Assuming an I TLB miss occurs, then entry 0 is loaded.
MCR to CP15 register 10, opcode_2 = 0x1, Base Value = 1, Current Victim = 1, P =
0
Example 2-4 Load a single entry into D TLB location 0, make it immune to
Invalidate All and lock it down
MCR to CP15 register 10, opcode_2 = 0x0, Base Value = 0,
Current Victim = 0, P = 1
Data load (LDR/LDM) or store (STR/STM). Assuming a D TLB miss occurs, then entry
0 is loaded.
MCR to CP15 register 10, opcode_2 = 0x0, Base Value = 1, Current Victim = 1, P =
0
2.3.15
Registers 11, 12, and 14, reserved
Accessing (reading or writing) any of these registers causes unpredictable behavior.
2.3.16
Register 13, FCSE PID register
Register 13 is the Fast Context Switch Extension (FCSE) Process Identifier (PID)
register. The FCSE PID register is 0x0 on reset.
Reading from CP15 register 13 returns the value of the FCSE PID. Writing CP15
register 13 updates the FCSE PID to the value in bits [31:25]. Bits [24:0] should be zero.
Register 13 bit assignments are shown in Figure 2-9.
31
25 24
FCSE PID
0
SBZ
Figure 2-9 Register 13
2-24
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Programmer’s Model
You can access register 13 using the following instructions:
MRC p15, 0, Rd, c13, c0, 0
MCR p15, 0, Rd, c13, c0, 0
;read FCSE PID
;write FCSE PID
Using the FCSE process identifier (FCSE PID)
Addresses issued by the ARM9TDMI core in the range 0 to 32MB are translated by
CP15 register 13, the FCSE PID register. Address A becomes A + (FCSE_PID x 32MB).
It is this translated address that is seen by both the caches and MMU. See Processor
functional block diagram on page 1-3. Addresses above 32MB undergo no translation.
This is shown in Figure 2-10 on page 2-25.
The FCSE_PID is a 7-bit field, enabling 128 x 32MB processes to be mapped.
Note
If FCSE_PID is zero, as it is on reset, then there is a flat mapping between the
ARM9TDMI and the caches and MMU.
Virtual address (VA)
issued by ARM9TDMI
Modified virtual address (MVA)
input to caches and MMU
4GB
4GB
127
2
1
32MB
0
C13
0
64MB
32MB
0
Figure 2-10 Address mapping using CP15 Register 13
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
2-25
Programmer’s Model
Changing the FCSE PID, performing a fast context switch
To do a fast context switch, write to CP15 register 13. The contents of the caches and
TLBs do not have to be flushed after a fast context switch because they still hold valid
address tags. The two instructions after the MCR to write the FCSE_PID are fetched with
the old FCSE_PID value:
{FCSE_PID = 0}
MOV r0, #1:SHL:25
MCR p15,0,r0,c13,c0,0
A1
A2
A3
2.3.17
;
;
;
;
;
Fetched
Fetched
Fetched
Fetched
Fetched
with
with
with
with
with
FCSE_PID
FCSE_PID
FCSE_PID
FCSE_PID
FCSE_PID
=
=
=
=
=
0
0
0
0
1
Register 15, test configuration register
Register 15 is used for test purposes. Accessing (reading or writing) this register causes
the ARM920T to have unpredictable behavior.
2-26
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Chapter 3
Memory Management Unit
This chapter describes the Memory Management Unit (MMU). It contains the following
sections:
•
About the MMU on page 3-2
•
MMU program accessible registers on page 3-4
•
Address translation on page 3-6
•
MMU faults and CPU aborts on page 3-21
•
Fault address and fault status registers on page 3-22
•
Domain access control on page 3-23
•
Fault checking sequence on page 3-25
•
External aborts on page 3-28
•
Interaction of the MMU and caches on page 3-29.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
3-1
Memory Management Unit
3.1
About the MMU
ARM920T processor implements an enhanced ARM architecture v4 MMU to provide
translation and access permission checks for the instruction and data address ports of
the ARM9TDMI core. The MMU is controlled from a single set of two-level page tables
stored in main memory, that are enabled by the M bit in CP15 register 1, providing a
single address translation and protection scheme. You can independently lock and flush
the instruction and data TLBs in the MMU.
The MMU features are:
3.1.1
•
standard ARMv4 MMU mapping sizes, domains, and access protection scheme
•
mapping sizes are 1MB (sections), 64KB (large pages), 4KB (small pages), and
1KB (tiny pages)
•
access permissions for sections
•
access permissions for large pages and small pages can be specified separately for
each quarter of the page (these quarters are called subpages)
•
16 domains implemented in hardware
•
64 entry instruction TLB and 64 entry data TLB
•
hardware page table walks
•
round-robin replacement algorithm (also called cyclic)
•
invalidate whole TLB, using CP15 register 8
•
invalidate TLB entry, selected by MVA, using CP15 register 8
•
independent lockdown of instruction TLB and data TLB, using CP15 register 10.
Access permissions and domains
For large and small pages, access permissions are defined for each subpage (1KB for
small pages, 16KB for large pages). Sections and tiny pages have a single set of access
permissions.
All regions of memory have an associated domain. A domain is the primary access
control mechanism for a region of memory. It defines the conditions necessary for an
access to proceed. The domain determines if:
•
the access permissions are used to qualify the access
•
the access is unconditionally allowed to proceed
•
the access is unconditionally aborted.
3-2
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Memory Management Unit
In the latter two cases, the access permission attributes are ignored.
There are 16 domains. These are configured using the domain access control register.
3.1.2
Translated entries
Each TLB caches 64 translated entries. During CPU memory accesses, the TLB
provides the protection information to the access control logic.
If the TLB contains a translated entry for the MVA, the access control logic determines
if access is permitted:
•
if access is permitted and an off-chip access is required, the MMU outputs the
appropriate physical address corresponding to the MVA
•
if access is permitted and an off-chip access is not required, the cache services the
access
•
if access is not permitted, the MMU signals the CPU core to abort.
If a TLB misses (it does not contain an entry for the VA) the translation table walk
hardware is invoked to retrieve the translation information from a translation table in
physical memory. When retrieved, the translation information is written into the TLB,
possibly overwriting an existing value.
The entry to be written is chosen by cycling sequentially through the TLB locations. To
enable use of TLB locking features, you can specify the location to write using CP15
register 10, TLB lockdown.
When the MMU is turned off, as happens on reset, no address mapping occurs and all
regions are marked as noncachable and nonbufferable. See About the caches and write
buffer on page 4-2.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
3-3
Memory Management Unit
3.2
MMU program accessible registers
Table 3-1 lists the CP15 registers that are used in conjunction with page table
descriptors stored in memory to determine the operation of the MMU.
Table 3-1 CP15 register functions
Register
Number
Bits
Register description
Control register
1
M, A, S, R
Contains bits to enable the MMU (M bit), enable data address
alignment checks (A bit), and to control the access protection
scheme (S bit and R bit).
Translation table
base register
2
31:14
Holds the physical address of the base of the translation table
maintained in main memory. This base address must be on a 16KB
boundary and is common to both TLBs.
Domain access
control register
3
31:0
Comprises 16 2-bit fields. Each field defines the access control
attributes for one of 16 domains (D15–D0).
Fault status
register
5 (I and D)
7:0
Indicates the cause of a Data or Prefetch Abort, and the domain
number of the aborted access, when an abort occurs. Bits 7:4 specify
which of the 16 domains (D15–D0) was being accessed when a fault
occurred. Bits 3:0 indicate the type of access being attempted. The
value of all other bits is unpredictable. The encoding of these bits is
shown in Table 3-9 on page 3-22.
Fault address
register
6 (D)
31:0
Holds the MVA associated with the access that caused the Data
Abort. See Table 3-9 on page 3-22 for details of the address stored
for each type of fault.
You can use ARM9TDMI register 14 to determine the MVA
associated with a Prefetch Abort.
TLB operations
register
8
31:0
You can write to this register to make the MMU perform TLB
maintenance operations. These are either invalidating all the
(unpreserved) entries in the TLB, or invalidating a specific entry.
TLB lockdown
register
10 (I and D)
31:20 and 0
Allows specific page table entries to be locked into the TLB and the
TLB victim index to be read or written:
opcode 2 = 0x0 accesses the D TLB lockdown register
•
•
opcode 2 = 0x1 accesses the I TLB lockdown register.
Locking entries in the TLB guarantees that accesses to the locked
page or section can proceed without incurring the time penalty of a
TLB miss. This allows the execution latency for time-critical pieces
of code such as interrupt handlers to be minimized.
3-4
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Memory Management Unit
All the CP15 MMU registers, except register 8, contain state. You can read them using
MRC instructions, and write them using MCR instructions. Registers 5 and 6 are also written
by the MMU during a Data Abort. Writing to Register 8 causes the MMU to perform a
TLB operation, to manipulate TLB entries. This register cannot be read. The Instruction
TLB (I TLB) and Data TLB (D TLB) both have a copy of register 10. The opcode_2 field
in the CP15 instruction is used to determine the one accessed.
CP15 is described in Chapter 2 Programmer’s Model, with details of register formats
and the coprocessor instructions you can use to access them.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
3-5
Memory Management Unit
3.3
Address translation
The MMU translates VAs generated by the CPU core, and by CP15 register 13, into
physical addresses to access external memory. It also derives and checks the access
permission, using a TLB.
The MMU table walking hardware is used to add entries to the TLB. The translation
information, that comprises both the address translation data and the access permission
data, resides in a translation table located in physical memory. The MMU provides the
logic for you to traverse this translation table and load entries into the TLB.
There are one or two stages in the hardware table walking, and permission checking,
process. The number of stages depends on whether the address is marked as a
section-mapped access or a page-mapped access.
There are three sizes of page-mapped accesses and one size of section-mapped access.
The page-mapped accesses are for:
•
large pages
•
small pages
•
tiny pages.
The translation process always starts out in the same way, with a level one fetch. A
section-mapped access requires only a level one fetch, but a page-mapped access
requires a subsequent level two fetch.
3.3.1
Translation table base
The hardware translation process is initiated when the TLB does not contain a
translation for the requested MVA. The Translation Table Base (TTB) register points to
the base address of a table in physical memory that contains section or page descriptors,
or both. The 14 low-order bits of the TTB register are set to zero on a read, and the table
must reside on a 16KB boundary. Figure 3-1 shows the format of the TTB register.
31
14 13
0
Translation table base
Figure 3-1 Translation table base register
The translation table has up to 4096 x 32-bit entries, each describing 1MB of virtual
memory. This allows up to 4GB of virtual memory to be addressed. Figure 3-2 on
page 3-7 shows the table walk process.
3-6
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Memory Management Unit
Level one fetch
Level two fetch
Translation
table
TTB base
Indexed by
modified
virtual
address
bits [31:20]
00
10
01
11
Section
Invalid
Section base
Indexed by
modified
virtual
address
bits [19:0]
1 MB
Large page base
4096 entries
Coarse page
table base
Indexed by
modified
virtual
address
bits [19:12]
Coarse page table
00
Invalid
Small page base
10
Invalid
256 entries
Indexed by
modified
virtual
address
bits [19:10]
Indexed by
modified
virtual
address
bits [11:0]
16 KB subpage
16 KB subpage
Small page
1 KB subpage
1 KB subpage
1 KB subpage
1 KB subpage
4 KB
Fine page table
00
16 KB subpage
64 KB
01
11
Fine page
table base
Indexed by
modified
virtual
address
bits [15:0]
Large page
16 KB subpage
Invalid
01
10
Tiny page base
11
Tiny page
Indexed by
modified
virtual
address
bits [9:0]
1024 entries
1 KB
Figure 3-2 Translating page tables
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
3-7
Memory Management Unit
3.3.2
Level one fetch
Bits [31:14] of the TTB register are concatenated with bits [31:20] of the MVA to
produce a 30-bit address as shown in Figure 3-3.
Modified virtual address
31
20 19
0
Table index
Translation table base
31
14 13
0
14 13
2 1 0
Translation base
31
Translation base
Table index
31
0 0
0
Level one descriptor
Figure 3-3 Accessing translation table level one descriptors
This address selects a 4-byte translation table entry. This is a level one descriptor for
either a section or a page table.
3.3.3
Level one descriptor
The level one descriptor returned is either a section descriptor, a coarse page table
descriptor, or a fine page table descriptor, or is invalid. Figure 3-4 on page 3-9 shows
the format of a level one descriptor.
3-8
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Memory Management Unit
31
20 19
12 11 10 9 8
Coarse page table base address
Section base address
AP
Fine page table base address
5 4 3 2 1 0
0 0
Fault
0 1
Coarse
page table
Domain
1
Domain
1 C B 1 0
Section
Domain
1
Fine
page table
1 1
Figure 3-4 Level one descriptor
A section descriptor provides the base address of a 1MB block of memory.
The page table descriptors provide the base address of a page table that contains level
two descriptors. There are two sizes of page table:
•
coarse page tables have 256 entries, splitting the 1MB that the table describes into
4KB blocks
•
fine page tables have 1024 entries, splitting the 1MB that the table describes into
1KB blocks.
Level one descriptor bit assignments are shown in Table 3-2.
Table 3-2 Level one descriptor bits
Bits
Description
ARM DDI 0151C
Section
Coarse
Fine
31:20
31:10
31:12
These bits form the corresponding bits of the physical
address
19:12
-
-
Should be zero
11:10
-
-
Access permission bits. Domain access control on
page 3-23 and Fault checking sequence on page 3-25 show
how to interpret the access permission bits
9
9
11:9
Should be zero
8:5
8:5
8:5
Domain control bits
Copyright © 2000, 2001 ARM Limited. All rights reserved.
3-9
Memory Management Unit
Table 3-2 Level one descriptor bits (continued)
Bits
Description
Section
Coarse
Fine
4
4
4
Must be 1
3:2
-
-
These bits, C and B, indicate whether the area of memory
mapped by this page is treated as write-back cachable,
write-through cachable, noncached buffered, or noncached
nonbuffered
-
3:2
3:2
Should be zero
1:0
1:0
1:0
These bits indicate the page size and validity and are
interpreted as shown in Table 3-3
The two least significant bits of the level one descriptor indicate the descriptor type as
shown in Table 3-3.
Table 3-3 Interpreting level one descriptor bits [1:0]
3.3.4
Value
Meaning
Description
00
Invalid
Generates a section translation fault
01
Coarse page table
Indicates that this is a coarse page table descriptor
10
Section
Indicates that this is a section descriptor
11
Fine page table
Indicates that this is a fine page table descriptor
Section descriptor
A section descriptor provides the base address of a 1MB block of memory. Figure 3-5
shows the format of a section descriptor.
31
20 19
Section base address
12 11 10 9 8
SBZ
AP
Domain
5 4 3 2 1 0
1 C B 1 0
SBZ
Figure 3-5 Section descriptor
3-10
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Memory Management Unit
Section descriptor bit assignments are described in Table 3-4.
Table 3-4 Section descriptor bits
3.3.5
Bits
Description
31:20
Form the corresponding bits of the physical address for a section
19:12
Always written as 0
11:10
(AP) Specify the access permissions for this section
9
Always written as 0
8:5
Specify one of the 16 possible domains (held in the domain access control register)
that contain the primary access controls
4
Should be written as 1, for backward compatibility
3:2
These bits (C and B) indicate whether the area of memory mapped by this section is
treated as write-back cachable, write-through cachable, noncached buffered, or
noncached nonbuffered
1:0
These bits must be 10 to indicate a section descriptor
Coarse page table descriptor
A coarse page table descriptor provides the base address of a page table that contains
level two descriptors for either large page or small page accesses. Coarse page tables
have 256 entries, splitting the 1MB that the table describes into 4KB blocks. Figure 3-6
shows the format of a coarse page table descriptor.
31
10 9 8
Coarse page table base address
Domain
5 4 3 2 1 0
1 SBZ 0 1
SBZ
Figure 3-6 Coarse page table descriptor
Note
If a coarse page table descriptor is returned from the level one fetch, a level two fetch is
initiated.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
3-11
Memory Management Unit
Coarse page table descriptor bit assignments are described in Table 3-5.
Table 3-5 Coarse page table descriptor bits
3.3.6
Bits
Description
31:10
These bits form the base for referencing the level two descriptor (the coarse page
table index for the entry is derived from the MVA)
9
Always written as 0
8:5
These bits specify one of the 16 possible domains (held in the domain access control
registers) that contain the primary access controls
4
Always written as 1
3:2
Always written as 0
1:0
These bits must be 01 to indicate a coarse page table descriptor
Fine page table descriptor
A fine page table descriptor provides the base address of a page table that contains level
two descriptors for large page, small page, or tiny page accesses. Fine page tables have
1024 entries, splitting the 1MB that the table describes into 1KB blocks. Figure 3-7
shows the format of a fine page table descriptor.
31
12 11
Fine page table base address
SBZ
9 8
Domain
5 4 3 2 1 0
1 SBZ 1 1
Figure 3-7 Fine page table descriptor
Note
If a fine page table descriptor is returned from the level one fetch, a level two fetch is
initiated.
3-12
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Memory Management Unit
Fine page table descriptor bit assignments are described in Table 3-6.
Table 3-6 Fine page table descriptor bits
3.3.7
Bits
Description
31:12
These bits form the base for referencing the level two descriptor (the fine page table
index for the entry is derived from the MVA)
11:9
Always written as 0
8:5
These bits specify one of the 16 possible domains (held in the domain access control
registers) that contain the primary access controls
4
Always written as 1
3:2
Always written as 0
1:0
These bits must be 11 to indicate a fine page table descriptor
Translating section references
Figure 3-8 on page 3-14 shows the complete section translation sequence.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
3-13
Memory Management Unit
Modified virtual address
31
20 19
0
Table index
Section index
Translation table base
31
14 13
0
14 13
2 1 0
Translation base
31
Translation base
Table index
0 0
Section level one descriptor
31
20 19
Section base address
12 11 10 9 8
AP
5 4 3 2 1 0
Domain 1 C B 1 0
Physical address
31
20 19
Section base address
0
Section index
Figure 3-8 Section translation
Note
You must check access permissions contained in the level one descriptor before
generating the physical address.
3.3.8
Level two descriptor
If the level one fetch returns either a coarse page table descriptor or a fine page table
descriptor, this provides the base address of the page table to be used. The page table is
then accessed and a level two descriptor is returned. Figure 3-9 on page 3-15 shows the
format of level two descriptors.
3-14
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Memory Management Unit
31
16 15
12 11 10 9 8 7 6 5 4 3 2 1 0
0 0
Fault
Large page base address
ap3
ap2 ap1
ap0
C B 0 1
Large page
Small page base address
ap3
ap2 ap1
ap0
C B 1 0
Small page
ap
C B 1 1
Tiny page
Tiny page base address
Figure 3-9 Level two descriptor
A level two descriptor defines a tiny, a small, or a large page descriptor, or is invalid:
•
a large page descriptor provides the base address of a 64KB block of memory
•
a small page descriptor provides the base address of a 4KB block of memory
•
a tiny page descriptor provides the base address of a 1KB block of memory.
Coarse page tables provide base addresses for either small or large pages. Large page
descriptors must be repeated in 16 consecutive entries. Small page descriptors must be
repeated in each consecutive entry.
Fine page tables provide base addresses for large, small, or tiny pages. Large page
descriptors must be repeated in 64 consecutive entries. Small page descriptors must be
repeated in four consecutive entries and tiny page descriptors must be repeated in each
consecutive entry.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
3-15
Memory Management Unit
Level two descriptor bit assignments are described in Table 3-7.
Table 3-7 Level two descriptor bits
Bits
Description
Large
Small
Tiny
31:16
31:12
31:10
These bits form the corresponding bits of the physical address
15:12
-
9:6
Should be zero
11:4
11:4
5:4
Access permission bits. Domain access control on page 3-23
and Fault checking sequence on page 3-25 show how to
interpret the access permission bits
3:2
3:2
3:2
These bits, C and B, indicate whether the area of memory
mapped by this page is treated as write-back cachable,
write-through cachable, noncached buffered, or noncached
nonbuffered
1:0
1:0
1:0
These bits indicate the page size and validity and are interpreted
as shown in Table 3-8
The two least significant bits of the level two descriptor indicate the descriptor type as
shown in Table 3-8.
Table 3-8 Interpreting page table entry bits [1:0]
Value
Meaning
Description
00
Invalid
Generates a page translation fault
01
Large page
Indicates that this is a 64KB page
10
Small page
Indicates that this is a 4KB page
11
Tiny page
Indicates that this is a 1KB page
Note
Tiny pages do not support subpage permissions and therefore only have one set of
access permission bits.
3-16
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Memory Management Unit
3.3.9
Translating large page references
Figure 3-10 shows the complete translation sequence for a 64KB large page.
Modified virtual address
31
20 19
Table index
16 15
L2
table index
12 11
0
Page index
Translation table base
31
14 13
0
14 13
2 1 0
Translation base
31
Translation base
Table index
0 0
Level one descriptor
31
10 9 8
Coarse page table base address
5 4 3 2 1 0
Domain 1
31
10 9
Coarse page table base address
0 1
2 1 0
L2 table index
0 0
Level two descriptor
31
16 15
Page base address
12 11 10 9 8 7 6 5 4 3 2 1 0
ap3 ap2 ap1 ap0 C B 0 1
Physical address
31
16 15
Page base address
0
Page index
Figure 3-10 Large page translation from a coarse page table
Because the upper four bits of the page index and low-order four bits of the coarse page
table index overlap, each coarse page table entry for a large page must be duplicated 16
times (in consecutive memory locations) in the coarse page table.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
3-17
Memory Management Unit
If a large page descriptor is included in a fine page table, the high-order six bits of the
page index and low-order six bits of the fine page table index overlap. Each fine page
table entry for a large page must therefore be duplicated 64 times.
3.3.10
Translating small page references
Figure 3-11 shows the complete translation sequence for a 4KB small page.
Modified virtual address
31
20 19
Table index
Level 2
table index
12 11
0
Page index
Translation table base
31
14 13
0
14 13
2 1 0
Translation base
31
Translation base
Table index
0 0
Level one descriptor
31
10 9 8
Coarse page table base address
5 4 3 2 1 0
Domain 1
31
10 9
Coarse page table base address
0 1
2 1 0
L2 table index
0 0
Level two descriptor
31
12 11 10 9 8 7 6 5 4 3 2 1 0
Page base address
ap3 ap2 ap1 ap0 C B 1 0
Physical address
31
12 11
Page base address
0
Page index
Figure 3-11 Small page translation from a coarse page table
3-18
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Memory Management Unit
If a small page descriptor is included in a fine page table, the upper two bits of the page
index and low-order two bits of the fine page table index overlap. Each fine page table
entry for a small page must therefore be duplicated four times.
3.3.11
Translating tiny page references
Figure 3-12 shows the complete translation sequence for a 1KB tiny page.
Modified virtual address
31
20 19
Level 2
table index
Table index
10 9
0
Page index
Translation table base
31
14 13
0
14 13
2 1 0
Translation base
31
Translation base
Table index
0 0
Level one descriptor
31
12 11
9 8
Fine page table base address
31
5 4 3 2 1 0
Domain 1
12 11
1 1
2 1 0
Fine page table base address
L2 table index
0 0
Level two descriptor
31
10 9
Page base address
6 5 4 3 2 1 0
ap C B 1 1
Physical address
31
10 9
Page base address
0
Page index
Figure 3-12 Tiny page translation from a fine page table
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
3-19
Memory Management Unit
Page translation involves one additional step beyond that of a section translation. The
level one descriptor is the fine page table descriptor and this is used to point to the level
one descriptor.
Note
The domain specified in the level one description and access permissions specified in
the level one description together determine whether the access has permissions to
proceed. See section Domain access control on page 3-23 for details.
3.3.12
Subpages
You can define access permissions for subpages of small and large pages. If, during a
page walk, a small or large page has a non-identical subpage permission, only the
subpage being accessed is written into the TLB. For example, a 16KB (large page)
subpage entry is written into the TLB if the subpage permission differs, and a 64KB
entry is put in the TLB if the subpage permissions are identical.
When you use subpage permissions, and the page entry then has to be invalidated, you
must invalidate all four subpages separately.
3-20
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Memory Management Unit
3.4
MMU faults and CPU aborts
The MMU generates an abort on the following types of faults:
•
alignment faults (data accesses only)
•
translation faults
•
domain faults
•
permission faults.
In addition, an external abort can be raised by the external system. This can happen only
for access types that have the core synchronized to the external system:
•
noncachable loads
•
nonbufferable writes.
Alignment fault checking is enabled by the A bit in CP15 register 1. Alignment fault
checking is not affected by whether or not the MMU is enabled. Translation, domain,
and permission faults are only generated when the MMU is enabled.
The access control mechanisms of the MMU detect the conditions that produce these
faults. If a fault is detected as a result of a memory access, the MMU aborts the access
and signals the fault condition to the CPU core. The MMU retains status and address
information about faults generated by the data accesses in the fault status register and
fault address register (see Fault address and fault status registers on page 3-22). The
MMU does not retain status about faults generated by instruction fetches.
An access violation for a given memory access inhibits any corresponding external
access, with an abort returned to the CPU core.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
3-21
Memory Management Unit
3.5
Fault address and fault status registers
On a Data Abort, the MMU places an encoded 4-bit value, FS[3:0], along with the 4-bit
encoded domain number, in the data FSR. Similarly, on a Prefetch Abort, in the prefetch
FSR, intended for debug purposes only. In addition, the MVA associated with the Data
Abort is latched into the FAR. If an access violation simultaneously generates more than
one source of abort, they are encoded in the priority given in Table 3-9. The FAR is not
updated by faults caused by instruction prefetches.
3.5.1
Fault status
Table 3-9 describes the various access permissions and controls supported by the data
MMU and details how these are interpreted to generate faults.
Table 3-9 Priority encoding of fault status
Priority
Source
Size
Status
Domain
FAR
Highest
Alignment
-
b00x1
Invalid
MVA of access causing
abort
Translation
Section
Page
b0101
b0111
Invalid
Valid
MVA of access causing
abort
Domain
Section
Page
b1001
b1011
Valid
Valid
MVA of access causing
abort
Permission
Section
Page
b1101
b1111
Valid
Valid
MVA of access causing
abort
External abort on noncachable nonbufferable
access or noncachable bufferable read
Section
Page
b1000
b1010
Valid
Valid
MVA of access causing
abort
Lowest
Note
For data FSR only, alignment faults can write either b0001 or b0011 into FS[3:0].
Invalid values in domains 3:0 can occur because the fault is raised before a valid domain
field has been read from a page table descriptor. Any abort masked by the priority
encoding can be regenerated by fixing the primary abort and restarting the instruction.
For instruction FSR only, the same priority applies as for the data FSR, except that
alignment faults cannot occur, and external aborts apply only to noncachable reads.
3-22
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Memory Management Unit
3.6
Domain access control
MMU accesses are primarily controlled through the use of domains. There are 16
domains and each has a 2-bit field to define access to it. Two types of user are supported,
clients and managers. The domains are defined in the domain access control register.
Figure 3-13 shows how the 32 bits of the register are allocated to define the 16 2-bit
domains.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Figure 3-13 Domain access control register format
Table 3-10 defines how the bits within each domain are interpreted to specify the access
permissions.
Table 3-10 Interpreting access control bits in domain access control register
ARM DDI 0151C
Value
Meaning
Description
00
No access
Any access generates a domain fault
01
Client
Accesses are checked against the access permission bits in the section
or page descriptor
10
Reserved
Reserved. Currently behaves like the no access mode
11
Manager
Accesses are not checked against the access permission bits so a
permission fault cannot be generated
Copyright © 2000, 2001 ARM Limited. All rights reserved.
3-23
Memory Management Unit
Table 3-11 shows how to interpret the Access Permission (AP) bits and how their
interpretation is dependent on the S and R bits (control register bits 8 and 9).
Table 3-11 Interpreting access permission (AP) bits
3-24
AP
S
R
Supervisor
permissions
User
permissions
00
0
0
No access
No access
Any access generates a permission
fault
00
1
0
Read-only
No access
Only Supervisor read permitted
00
0
1
Read-only
Read-only
Any write generates a permission fault
00
1
1
Reserved
-
-
01
x
x
Read/write
No access
Access allowed only in Supervisor
mode
10
x
x
Read/write
Read-only
Writes in User mode cause permission
fault
11
x
x
Read/write
Read/write
All access types permitted in both
modes
xx
1
1
Reserved
-
-
Description
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Memory Management Unit
3.7
Fault checking sequence
The sequence the MMU uses to check for access faults is different for sections and
pages. The sequence for both types of access is shown in Figure 3-14.
Modified virtual address
Check address alignment
Section
translation
fault
Invalid
Misaligned
Alignment
fault
Invalid
Page
translation
fault
No access (00)
Reserved (10)
Page
domain
fault
Violation
Page
permission
fault
Get level one descriptor
Page
Section
Get page
table entry
Section
domain
fault
No access (00)
Reserved (10)
Check domain status
Section
Page
Client (01)
Client (01)
Manager
(11)
Section
permission
fault
Violation
Check
access
permissions
Check
access
permissions
Physical address
Figure 3-14 Sequence for checking faults
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
3-25
Memory Management Unit
The conditions that generate each of the faults are described in:
•
Alignment fault on page 3-26
•
Translation fault on page 3-26
•
Domain fault on page 3-26
•
Permission fault on page 3-27.
3.7.1
Alignment fault
If alignment fault is enabled (A bit in CP15 register 1 set), the MMU generates an
alignment fault on any data word access, if the address is not word-aligned, or on any
halfword access, if the address is not halfword-aligned, irrespective of whether the
MMU is enabled or not. An alignment fault is not generated on any instruction fetch,
nor on any byte access.
Note
If the access generates an alignment fault, the access sequence aborts without reference
to more permission checks.
3.7.2
Translation fault
There are two types of translation fault:
3.7.3
Section
A section translation fault is generated if the level one descriptor is
marked as invalid. This happens if bits [1:0] of the descriptor are both 0.
Page
A page translation fault is generated if the level one descriptor is marked
as invalid. This happens if bits [1:0] of the descriptor are both 0.
Domain fault
There are two types of domain fault:
3-26
Section
The level one descriptor holds the 4-bit domain field, which selects one
of the 16 2-bit domains in the domain access control register. The two bits
of the specified domain are then checked for access permissions as
described in Table 3-11 on page 3-24. The domain is checked when the
level one descriptor is returned.
Page
The level one descriptor holds the 4-bit domain field, which selects one
of the 16 2-bit domains in the domain access control register. The two bits
of the specified domain are then checked for access permissions as
described in Table 3-11 on page 3-24. The domain is checked when the
level one descriptor is returned.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Memory Management Unit
If the specified access is either no access (00) or reserved (10) then either a section
domain fault or page domain fault occurs.
3.7.4
Permission fault
If the 2-bit domain field returns 01 (client) then access permissions are checked as
follows:
Section
If the level one descriptor defines a section-mapped access, the AP bits of
the descriptor define whether or not the access is allowed, according to
Table 3-11 on page 3-24. Their interpretation is dependent on the setting
of the S and R bits (control register bits 8 and 9). If the access is not
allowed, a section permission fault is generated.
Large page or small page
If the level one descriptor defines a page-mapped access and the level two
descriptor is for a large or small page, four access permission fields
(ap3-ap0) are specified, each corresponding to one quarter of the page.
For small pages ap3 is selected by the top 1KB of the page and ap0 is
selected by the bottom 1KB of the page. For large pages, ap3 is selected
by the top 16KB of the page and ap0 is selected by the bottom 16KB of
the page. The selected AP bits are then interpreted in exactly the same
way as for a section (see Table 3-11 on page 3-24). The only difference
is that the fault generated is a page permission fault.
Tiny page
ARM DDI 0151C
If the level one descriptor defines a page-mapped access and the level two
descriptor is for a tiny page, the AP bits of the level one descriptor define
whether or not the access is allowed in the same way as for a section. The
fault generated is a page permission fault.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
3-27
Memory Management Unit
3.8
External aborts
In addition to the MMU-generated aborts, the ARM920T can be externally aborted by
the AMBA bus. This can be used to flag an error on an external memory access.
However, not all accesses can be aborted in this way and the Bus Interface Unit (BIU)
ignores external aborts that cannot be handled.
The following accesses can be aborted:
•
noncached reads
•
unbuffered writes
•
read-lock-write sequence, to noncachable memory.
In the case of a read-lock-write (SWP) sequence, if the read aborts the write is always
attempted.
3-28
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Memory Management Unit
3.9
Interaction of the MMU and caches
The MMU is enabled and disabled using bit 0 of the CP15 control register as described
in:
•
Enabling the MMU on page 3-29
•
Disabling the MMU on page 3-29.
3.9.1
Enabling the MMU
To enable the MMU:
1.
Program the TTB and domain access control registers.
2.
Program level 1 and level 2 page tables as required.
3.
Enable the MMU by setting bit 0 in the control register.
You must take care if the translated address differs from the untranslated address
because several instructions following the enabling of the MMU might have been
prefetched with the MMU off (using physical = VA - flat translation).
In this case, enabling the MMU can be considered as a branch with delayed execution.
A similar situation occurs when the MMU is disabled. Consider the following code
sequence:
MRC p15,0,R1,C1,C0,0
ORR R1, #0x1
MCR p15,0,R1,C1,C0,0
Fetch Flat
Fetch Flat
Fetch Translated
; Read control register
; Enable MMUS
You can enable the ICache and DCache simultaneously with the MMU using a single
MCR instruction.
3.9.2
Disabling the MMU
To disable the MMU, clear bit 0 in the control register. The data cache must be disabled
prior to, or at the same time as, the MMU is disabled by clearing bit 2 of the control
register. See Enabling the MMU regarding prefetch effects.
Note
If the MMU is enabled, then disabled and subsequently re-enabled, the contents of the
TLBs are preserved. If these are now invalid, you must invalidate the TLBs before
re-enabling the MMU. See Register 8, TLB operations register on page 2-19.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
3-29
Memory Management Unit
3-30
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Chapter 4
Caches, Write Buffer, and Physical Address
TAG (PA TAG) RAM
This chapter describes the Instruction Cache (ICache), Data Cache (DCache), write
buffer, and Physical Address (PA) TAG RAM. It contains the following sections:
•
About the caches and write buffer on page 4-2
•
ICache on page 4-4
•
DCache and write buffer on page 4-9
•
Cache coherence on page 4-17
•
Cache cleaning when lockdown is in use on page 4-20
•
Implementation notes on page 4-21
•
Physical address TAG RAM on page 4-22
•
Drain write buffer on page 4-23
•
Wait for interrupt on page 4-24.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
4-1
Caches, Write Buffer, and Physical Address TAG (PA TAG) RAM
4.1
About the caches and write buffer
The ARM920T level-one memory system includes an Instruction Cache (ICache), a
Data Cache (DCache), a write buffer, and a Physical Address (PA) TAG RAM to reduce
the effect of main memory bandwidth and latency on performance.
The ARM920T processor implements separate 16KB instruction and 16KB data caches
(ICache and DCache).
The caches have the following features:
4-2
•
Virtually-addressed 64-way associative cache.
•
8 words per line (32 bytes per line) with one valid bit and two dirty bits per line,
allowing half-line write-backs.
•
Write-through and write-back cache operation (write-back caches are also known
as copy-back caches), selected per memory region by the C and B bits in the
MMU translation tables (for data cache only).
•
Pseudo-random or round-robin replacement, selectable using the RR bit in CP15
register 1.
•
Low-power CAM-RAM implementation.
•
Caches independently lockable with granularity of 1/64th of cache, which is
64 words (256 bytes).
•
To avoid a TLB miss during write-back data eviction, and to reduce interrupt
latency, the physical address corresponding to each data cache entry is stored in
the PA TAG RAM for use during cache line write-backs, in addition to the VA
TAG stored in the cache CAMs. This means that the MMU is not involved in
cache write-back operations, removing the possibility of TLB misses related to
the write-back address.
•
Cache maintenance operations to provide efficient cleaning of the entire data
cache, and to provide efficient cleaning and invalidation of small regions of
virtual memory. The latter allows ICache coherency to be efficiently maintained
when small code changes occur, for example self-modifying code and changes to
exception vectors.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Caches, Write Buffer, and Physical Address TAG (PA TAG)
The write buffer:
•
has a 16-word data buffer
•
has a 4-address address buffer
•
can be drained under software control, using a CP15 MCR instruction (see Drain
write buffer on page 4-23).
The ARM920T can be drained under software control and put into a low-power state
until an interrupt occurs, using a CP15 MCR instruction (see Wait for interrupt on
page 4-24).
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
4-3
Caches, Write Buffer, and Physical Address TAG (PA TAG) RAM
4.2
ICache
The ARM920T includes a 16KB ICache. The ICache has 512 lines of 32 bytes (8
words), arranged as a 64-way set-associative cache and uses MVAs, translated by CP15
register 13 (see Address translation on page 3-6), from the ARM9TDMI core.
The ICache implements allocate-on-read-miss. Random or round-robin replacement
can be selected under software control using the RR bit (CP15 register 1, bit 14).
Random replacement is selected at reset.
Instructions can also be locked in the ICache so that they cannot be overwritten by a
linefill. This operates with a granularity of 1/64th of the cache, which is 64 words (256
bytes).
All instruction accesses are subject to MMU permission and translation checks.
Instruction fetches that are aborted by the MMU do not cause linefills or instruction
fetches to appear on the AMBA ASB interface.
Note
For clarity, the I bit (bit 12 in CP15 register 1) is called the Icr bit throughout the
following text. The C bit from the MMU translation table descriptor corresponding to
the address being accessed is called the Ctt bit.
4.2.1
ICache organization
The ICache is organized as eight segments, each containing 64 lines, and each line
containing eight words. The position of the line within the segment is a number from 0
to 63. This is called the index. A line in the cache can be uniquely identified by its
segment and index. The index is independent of the MVA. The segment is selected by
bits [7:5] of the MVA.
Bits [4:2] of the MVA specify the word within a cache line that is accessed. For
halfword operations, bit [1] of the MVA specifies the halfword that is accessed within
the word. For byte operations, bits [1:0] specify the byte within the word that is
accessed.
Bits [31:8] of the MVA of each cache line are called the TAG. The MVA TAG is stored
in the cache, along with the 8-words of data, when the line is loaded by a linefill.
Cache lookups compare bits [31:8] of the MVA of the access with the stored TAG to
determine whether the access is a hit or miss. The cache is therefore said to be virtually
addressed. The logical model of the 16KB ICache is shown in Figure 4-1 on page 4-5.
4-4
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Caches, Write Buffer, and Physical Address TAG (PA TAG)
Modified Virtual Address
31
8 7
5 4
Seg
TAG
2 1 0
Word
SEG 0 1
0
3
2
Byte
4
7
6
5
Decoder
7
0
TAG
Cache line/index
W0
CAM
W7
RAM
2KB RAM = 64 lines x 8 words
63
32
0
7
SEG 0 select
RDATA[31:0]
Figure 4-1 Addressing the 16KB ICache
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
4-5
Caches, Write Buffer, and Physical Address TAG (PA TAG) RAM
4.2.2
Enabling and disabling the ICache
On reset, the ICache entries are all invalidated and the ICache is disabled.
You can enable the ICache by writing 1 to the Icr bit, and disable it by writing 0 to the
Icr bit.
When the ICache is disabled, the cache contents are ignored and all instruction fetches
appear on the AMBA ASB interface as separate nonsequential accesses. The ICache is
usually used with the MMU enabled. In this case the Ctt in the relevant MMU
translation table descriptor indicates whether an area of memory is cachable.
If the cache is disabled after having been enabled, all cache contents are ignored. All
instruction fetches appear on the AMBA ASB interface as separate nonsequential
accesses and the cache is not updated. If the cache is subsequently re-enabled its
contents are unchanged. If the contents are no longer coherent with main memory, you
must invalidate the ICache before you re-enable it (see Register 7, cache operations
register on page 2-17).
If the cache is enabled with the MMU disabled, all instruction fetches are treated as
cachable. No protection checks are made, and the physical address is flat-mapped to the
modified virtual address.
You can enable the MMU and ICache simultaneously by writing a 1 to the M bit, and a
1 to the Icr bit in CP15 register 1, with a single MCR instruction.
Note
ARM920T implements a nonsequential access on the AMBA ASB interface as an
A-TRAN cycle followed by an S-TRAN cycle. It does not produce N-TRAN cycles. A
linefill appears as an A-TRAN cycle followed by an S-TRAN cycle.
4.2.3
ICache operation
If the ICache is disabled, each instruction fetch results in a separate nonsequential
memory access on the AMBA ASB interface, giving very low bus and memory
performance. Therefore, you must enable the ICache as soon as possible after reset.
If the ICache is enabled, an ICache lookup is performed for each instruction fetch
regardless of the setting of the Ctt bit in the relevant MMU translation table descriptor:
•
4-6
If the required instruction is found in the cache, the lookup is called a cache hit.
If the instruction fetch is a cache hit and Ctt=1, indicating a cachable region of
memory, then the instruction is returned from the cache to the ARM9TDMI CPU
core.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Caches, Write Buffer, and Physical Address TAG (PA TAG)
•
If the required instruction is not found in the cache, the lookup is called a cache
miss. If it is a cache miss and Ctt=1, then an eight-word linefill is performed,
possibly replacing another entry. The entry to be replaced, called the victim, is
chosen from the entries that are not locked, using either a random or round-robin
replacement policy.If Ctt=0, indicating a noncachable region of memory, then a
single nonsequential memory access appears on the AMBA ASB interface.
Note
If Ctt=0, indicating a noncachable region of memory, then the cache lookup results in a
cache miss. The only way that it can result in a cache hit is if software has changed the
value of the Ctt bit in the MMU translation table descriptor without invalidating the
cache contents. This is a programming error. The behavior in this case is architecturally
unpredictable and varies between implementations.
4.2.4
ICache replacement algorithm
The ICache and DCache replacement algorithm is selected by the RR bit in the CP15
control register (CP15 register 1, bit 14). Random replacement is selected at reset.
Setting the RR bit to 1 selects round-robin replacement. Round-robin replacement
means that entries are replaced sequentially in each cache segment.
4.2.5
ICache lockdown
You can lock instructions into the ICache, causing the ICache to guarantee a hit, and
provide optimum and predictable execution time. If you enable the ICache, an ICache
lookup is performed for each instruction fetch. If the ICache misses and the Ctt=1 then
an eight-word linefill is performed. The entry to be replaced is selected by the victim
pointer. You can lock instructions into the ICache by controlling the victim pointer, and
forcing prefetches to the ICache. You lock instructions in the ICache by first ensuring
the code to be locked is not already in the cache. You can ensure this by invalidating
either the whole ICache or specific lines:
MCR p15, 0, Rd, c7, c5, 0
MCR p15, 0, Rd, c7, c5, 1
; Invalidate ICache
; Invalidate ICache line using MVA
You can then use a short software routine to load the instructions into the ICache. The
software routine must either be noncachable, or already in the ICache but not in an
ICache line about to be overwritten. You must enable the MMU to ensure that any TLB
misses that occur while loading the instructions cause a page table walk. The software
routine operates by writing to CP15 register 9 to force the victim pointer to a specific
ICache line and by using the prefetch ICache line operation to force the ICache to
perform a lookup. This misses, assuming the code has been invalidated, and an 8-word
linefill is performed loading the cache line into the entry specified by the victim pointer.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
4-7
Caches, Write Buffer, and Physical Address TAG (PA TAG) RAM
When all the instructions have been loaded, they are then locked by writing to CP15
register 9 to set the victim pointer base to be one higher than the last entry written. All
further linefills now occur in the range victim base to 63.An example ICache lockdown
routine is shown in Example 4-1. The example assumes that the number of cache lines
to be loaded is not known. The address does not have to be cache line or word-aligned
but this is recommended to ensure future compatibility.
Note
The Prefetch ICache Line operation uses MVA format, because address aliasing is not
performed on the address in Rd. It is advisable for the associated TLB entry to be locked
into the TLB to avoid page table walks during execution of the locked code.
Example 4-1 ICache lockdown routine
loop
ADRL
ADRL
MOV
MCR
r0,start_address
r1,end_address
r2,#lockdown_base<<26
p15,0,r2,c9,c0,1
; address pointer
; victim pointer
; write ICache victim and lockdown base
MCR
ADD
p15,0,r0,c7,c13,1
r0,r0,#32
; Prefetch ICache line
; increment address pointer to next ICache line
;; do we need to increment the victim pointer?
;; test for segment 0, and if so, increment the victim pointer
;; and write the ICache victim and lockdown base.
AND
r3,r0,#0xE0
; extract the segment bits from the address
CMP
r3,#0x0
; test for segment 0
ADDEQ
r2,r2,#0x1<<26
; if segment 0, increment victim pointer
MCREQ
p15,0,r2,c9,c0,1
; and write ICache victim and lockdown base
;; have we linefilled enough code?
;; test for the address pointer being less than or equal to the
;; end_address and if so, loop and perform another linefill
CMP
r0,r1
; test for less than or equal to end_address
BLE
loop
; if not, loop
;;
;;
;;
;;
;;
4-8
have we exited with r3 pointing to segment 0?
if so, the ICache victim and lockdown base has already been set to one
higher than the last entry written.
if not, increment the victim pointer and write the ICache victim and
lockdown base.
CMP
r3,#0x0
; test for segments 1 to 7
ADDNE
r2,r2,#0x1<<26
; if address is segment 1 to 7,
MCRNE
p15,0,r2,c9,c0,1
; write ICache victim and lockdown base
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Caches, Write Buffer, and Physical Address TAG (PA TAG)
4.3
DCache and write buffer
The ARM920T processor includes a 16KB DCache and a write buffer to reduce the
effect of main memory bandwidth and latency on data access performance. The DCache
has 512 lines of 32 bytes (8-words), arranged as a 64-way set-associative cache and uses
MVAs translated by CP15 register 13 (see Address translation on page 3-6) from the
ARM9TDMI CPU core. The write buffer can hold up to 16 words of data and four
separate addresses. The operations of the DCache and the write buffer are closely
connected.
The DCache supports write-through and write-back memory regions, controlled by the
C and B bits in each section and page descriptor within the MMU translation tables. For
clarity, these bits are called Ctt and Btt in the following text. For details see DCache and
write buffer operation on page 4-10.
Each DCache line has two dirty bits, one for the first four words of the line, the other
for the last four words, and a single virtual TAG address and valid bit for the entire
8-word line. The physical address from which each line is loaded is stored in the PA
TAG RAM and is used when writing modified lines back to memory.
When a store hits in the DCache, if the memory region is write-back, the associated
dirty bit is set marking the appropriate half-line as being modified. If the cache line is
replaced due to a linefill, or if the line is the target of a DCache clean operation, the dirty
bits are used to decide whether the whole, half, or none of the line is written back to
memory. The line is written back to the same physical address from which it was loaded,
regardless of any changes to the MMU translation tables.
The DCache implements allocate-on-read-miss. Random or round-robin replacement
can be selected under software control by the RR bit (CP15 register 1, bit 14). Random
replacement is selected at reset. A linefill always loads a complete 8-word line.
Data can also be locked in the DCache so that it cannot be overwritten by a linefill. This
operates with a granularity of 1/64 th of the cache, which is 64 words (256 bytes).
All data accesses are subject to MMU permission and translation checks. Data accesses
that are aborted by the MMU do not cause linefills or data accesses to appear on the
AMBA ASB interface.
For clarity, the C bit (bit 2 in CP15 register 1) is called the Ccr bit throughout the
following text.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
4-9
Caches, Write Buffer, and Physical Address TAG (PA TAG) RAM
4.3.1
Enabling and disabling the DCache and write buffer
On reset, the DCache entries are invalidated and the DCache is disabled, and the write
buffer contents are discarded.
There is no explicit write buffer enable bit implemented in ARM920T. The write buffer
is used in the following ways:
4.3.2
•
You can enable the DCache by writing 1 to the Ccr bit, and disable it by writing
0 to the Ccr bit.
•
You must only enable the DCache when the MMU is enabled. This is because the
MMU translation tables define the cache and write buffer configuration for each
memory region.
•
If the DCache is disabled after having been enabled, the cache contents are
ignored and all data accesses appear on the AMBA ASB interface as separate
nonsequential accesses and the cache is not updated. If the cache is subsequently
re-enabled its contents are unchanged. Depending on the software system design,
you might have to clean the cache after it is disabled, and invalidate it before you
re-enable it. See Cache coherence on page 4-17.
•
You can enable or disable the MMU and DCache simultaneously with a single MCR
that changes the M bit and the C bit in the control register (CP15 register 1).
DCache and write buffer operation
The DCache and write buffer configuration of each memory region is controlled by the
Ctt and Btt bits in each section and page descriptor in the MMU translation tables. You
can modify the configuration using the DCache enable bit in the CP15 control register.
This is called Ccr.
If the DCache is enabled, a DCache lookup is performed for each data access initiated
by the ARM9TDMI CPU core, regardless of the value of the Ctt bit in the relevant
MMU translation table descriptor. If the required data is found, the lookup is called a
cache hit. If the required data is not found, the lookup is called a cache miss. In this
context a data access means any type of load (read), store (write), or swap instruction,
including LDR, LDRB, LDRH, LDM, LDC, STR, STRB, STRH, STC, SWP, and SWPB.
Accesses appear on the AMBA ASB interface in program order but the ARM9TDMI
CPU core can continue executing at full speed, reading instructions and data from the
caches, and writing to the DCache and write buffer, while buffered writes are being
written to memory through the AMBA ASB interface.
4-10
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Caches, Write Buffer, and Physical Address TAG (PA TAG)
Table 4-1 describes the DCache and write buffer behavior for each type of memory
configuration. Ctt AND Ccr means the bitwise Boolean AND of Ctt with Ccr.
Table 4-1 DCache and write buffer configuration
Ctt AND
Ccr
Btt
DCache, write buffer, and memory access behavior
0a
0
Noncached, nonbuffered (NCNB).
Reads and writes are not cached. They always perform accesses on the
AMBA ASB interface.
Writes are not buffered. The CPU halts until the write is completed on
the AMBA ASB interface.
Reads and writes can be externally aborted.
Cache hits never occur under normal operation.b
ARM DDI 0151C
0
1
Noncached, buffered (NCB).
Reads and writes are not cached, and always perform accesses on the
AMBA ASB interface.
Writes are placed in the write buffer and appear on the AMBA ASB
interface. The CPU continues execution as soon as the write is placed
in the write buffer.
Reads can be externally aborted.
Writes cannot be externally aborted.Cache hits never occur under
normal operation.b
1
0
Cached write-through mode (WT).
Reads that hit in the cache read the data from the cache and do not
perform an access on the AMBA ASB interface.
Reads that miss in the cache cause a linefill.
Writes that hit in the cache update the cache.
All writes are placed in the write buffer and appear on the AMBA
ASB interface.
The CPU continues execution as soon as the write is placed in the
write buffer.
Reads and writes cannot be externally aborted.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
4-11
Caches, Write Buffer, and Physical Address TAG (PA TAG) RAM
Table 4-1 DCache and write buffer configuration (continued)
Ctt AND
Ccr
Btt
DCache, write buffer, and memory access behavior
1
1
Cached write-back mode (WB).
Reads that hit in the cache read the data from the cache and do not
perform an AMBA ASB interface access.
Reads that miss in the cache cause a linefill.
Writes that hit in the cache update the cache and mark the appropriate
half of the cache line as dirty, and do not cause an AMBA ASB
interface access.
Writes that miss in the cache are placed in the write buffer and appear
on the AMBA ASB interface. The CPU continues execution as soon
as the write is placed in the write buffer.
Cache write-backs are buffered.
Reads, writes, and write-backs cannot be externally aborted.
a. If the control register C bit (Ccr) is zero, it disables all lookups in the cache, while if the
translation table descriptor C bit (Ctt) is zero, it only stops new data being loaded into the
cache. With Ccr = 1 and Ctt = 0 the cache is still searched on every access to check whether
the cache contains an entry for the data.
b. It is an operating system software error if a cache hit occurs when reading from, or writing to,
a region of memory marked as NCNB or NCB. The only way this can occur is if the operating
system changes the value of the C and B bits in a page table descriptor, while the cache
contains data from the area of virtual memory controlled by that descriptor. The cache and
memory system behavior resulting from changing the page table descriptor in this way is
unpredictable. If the operating system has to change the C and B bits of a page table descriptor,
it must ensure that the caches do not contain any data controlled by that descriptor. In some
circumstances, the operating system might have to clean and flush the caches to ensure this.
A linefill performs an 8-word burst read from the AMBA ASB interface and places it
as a new entry in the cache, possibly replacing another line at the same location within
the cache. The location that is replaced, called the victim, is chosen from the entries that
are not locked using either a random or round-robin replacement policy. If the cache line
being replaced is marked as dirty, indicating that it has been modified and that main
memory has not been updated to reflect the change, a cache writeback occurs.
Depending on whether one or both halves of the cache line are dirty, the write-back
performs a 4 or 8-word sequential burst write access on the AMBA ASB interface. The
write-back data is placed in the write buffer, and then the linefill data is read from the
AMBA ASB interface. The CPU can then continue while the write-back data is written
to memory over the AMBA ASB interface.
Load multiple (LDM) instructions accessing NCNB or NCB regions perform sequential
bursts on the AMBA ASB interface. Store multiple (STM) instructions accessing NCNB
regions also perform sequential bursts on the AMBA ASB interface.
4-12
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Caches, Write Buffer, and Physical Address TAG (PA TAG)
The sequential burst is split into two bursts if it crosses a 1KB boundary. This is because
the smallest MMU protection and mapping size is 1KB, so the memory regions on each
side of the 1KB boundary can have different properties.
This means that sequential accesses generated by ARM920T do not cross a 1KB
boundary. This can be exploited to simplify memory interface design. For example, a
simple page-mode DRAM controller can perform a page-mode access for each
sequential access, provided the DRAM page size is 1KB or larger.
See also Cache coherence on page 4-17.
4.3.3
DCache organization
The DCache is organized as eight segments, each containing 64 lines, and each line
containing eight words. The position of the line within the segment is a number from 0
to 63. This is called the index. A line in the cache can be uniquely identified by its
segment and index. The index is independent of the MVA. The segment is selected by
bits [7:5] of the MVA.
Bits [4:2] of the MVA specify which word within a cache line is accessed. For halfword
operations, bit [1] of the MVA specifies which halfword is accessed within the word.
For byte operations, bits [1:0] specify which byte within the word is accessed.
Bits [31:8] of the MVA of each cache line are called the TAG. The MVA TAG is stored
in the cache, along with the eight words of data, when the line is loaded by a linefill.
Cache lookups compare bits [31:8] of the MVA of the access with the stored TAG to
determine whether the access is a hit or miss. The cache is therefore said to be virtually
addressed.
The DCache logical model is the same as for the ICache. See Addressing the 16KB
ICache on page 4-5.
4.3.4
DCache replacement algorithm
The DCache and ICache replacement algorithm is selected by the RR bit in the CP15
control register (CP15 register 1, bit 14). Random replacement is selected at reset.
Setting the RR bit to 1 selects round-robin replacement. Round-robin replacement
means that entries are replaced sequentially in each segment.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
4-13
Caches, Write Buffer, and Physical Address TAG (PA TAG) RAM
4.3.5
Swap instructions
Swap instruction (SWP or SWPB) behavior is dependent on whether the memory region is
cachable or noncachable.
Swap instructions to cachable regions of memory are useful for implementing
semaphores or other synchronization primitives in multithreaded uniprocessor software
systems.
Swap instructions to noncachable memory regions are useful for synchronization
between two bus masters in a multi-master bus system. This can be two processors, or
one processor and a DMA controller.
When a swap instruction accesses a cachable region of memory (write-through or
write-back), the DCache and write buffer behavior is the same as having a load followed
by a store according to the normal rules described. The BLOK pin is not asserted during
the execution of the instruction. It is guaranteed that no interrupt can occur between the
load and store portions of the swap.
When a swap instruction accesses a noncachable (NCB or NCNB) region of memory,
the write buffer is drained, and a single word or byte is read from the AMBA ASB
interface. The write portion of the swap is then treated as nonbufferable, regardless of
the value of Btt, and the processor is stalled until the write is completed on the AMBA
ASB interface. The BLOK pin is asserted to indicate that you can treat the read and
write as an atomic operation on the bus.
Like all other data accesses, a swap to a noncachable region that hits in the cache
indicates a programming error.
4.3.6
DCache lockdown
You can lock data into the DCache, causing the DCache to guarantee a hit, and provide
optimum and predictable execution time. If you enable the DCache, a DCache lookup
is performed for each load. If the DCache misses and the Ctt=1 then an eight-word
linefill is performed. The entry to be replaced is selected by the victim pointer. You can
lock data into the DCache by controlling the victim pointer, and forcing loads to the
DCache. You lock data in the DCache by first ensuring the data to be locked is not
already in the cache. You can ensure this by cleaning and invalidating either the whole
DCache or specific lines. Example 4-2 on page 4-15 shows DCache invalidate and clean
operations that you can perform to do this.
4-14
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Caches, Write Buffer, and Physical Address TAG (PA TAG)
Example 4-2 DCache invalidate and clean operations
MCR p15, 0, Rd, c7, c6, 0
; Invalidate DCache
MCR p15, 0, Rd, c7, c6, 1
; Invalidate DCache single entry using MVA
MCR p15, 0, Rd, c7, c10, 1
; Clean DCache single entry using MVA
MCR p15, 0, Rd, c7, c14, 1
; Clean and Invalidate DCache single entry using MVA
MCR p15, 0, Rd, c7, c10, 2
; Clean DCache single entry using Index
MCR p15, 0, Rd, c7, c14, 2
; Clean and Invalidate DCache single entry using Index
You can then use a short software routine to load the data into the DCache. You can
locate the software routine in a cachable region of memory providing it does not contain
any loads or stores. You must enable the MMU.The software routine operates by writing
to CP15 register 9 to force the victim pointer to a specific DCache line and by using an
LDR or LDM to force the DCache to perform a lookup. This misses, assuming the data was
previously invalidated, and an eight-word linefill is performed loading the cache line
into the entry specified by the victim pointer. When all the data has been loaded, it is
then locked by writing to CP15 register 9 to set the victim pointer base to be one higher
than the last entry written. All further linefills now occur in the range victim base to
63.An example DCache lockdown routine is shown in Example 4-3 on page 4-16. The
example assumes that the number of cache lines to be loaded is not known. The address
does not have to be cache line or word-aligned, although it is preferable for future
compatibility.
Note
The LDR or LDM uses VA format, because address aliasing is performed on the address.It
is advisable for the associated TLB entry to be locked into the TLB to avoid page table
walks during accesses of the locked data.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
4-15
Caches, Write Buffer, and Physical Address TAG (PA TAG) RAM
Example 4-3 DCache lockdown routine
ADRL
ADRL
MOV
MCR
r0,start_address
r1,end_address
r2,#lockdown_base<<26
p15,0,r2,c9,c0,0
; address pointer
; victim pointer
; write DCache victim and lockdown base
LDR
r3,[r0],#32
; load DCache line, increment to next DCache line
loop
;; do we need to increment the victim pointer?
;; test for segment 0, and if so, increment the victim pointer and
;; write the ICache victim and lockdown base.
AND
r3,r0,#0xE0
; extract the segment bits from the address
CMP
r3,#0x0
; test for segment 0
ADDEQ
r2,r2,#0x1<<26
; if segment 0, increment victim pointer
MCREQ
p15,0,r2,c9,c0,0
; and write DCache victim and lockdown base
;; have we linefilled enough code?
;; test for the address pointer being less than or equal to the end_address
;; and if so, loop and perform another linefill
CMP
r0,r1
; test for less than or equal to end_address,
BLE
loop
; if not, loop
;;
;;
;;
;;
;;
have we exited with r3 pointing to segment 0?
if so, the ICache victim and lockdown base has already been set to one
higher than the last entry written.
if not, increment the victim pointer and write the ICache victim and
lockdown base.
CMP
r3,#0x0
; test for segments 1 to 7
ADDNE
r2,r2,#0x1<<26
; if address is segment 1 to 7,
MCRNE
p15,0,r2,c9,c0,0
; write DCache victim and lockdown base
4-16
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Caches, Write Buffer, and Physical Address TAG (PA TAG)
4.4
Cache coherence
The ICache and DCache contain copies of information normally held in main memory.
If these copies of memory information get out of step with each other because one is
updated and the other is not updated, they are said to have become incoherent. If the
DCache contains a line that has been modified by a store or swap instruction, and the
main memory has not been updated, the cache line is said to be dirty. Clean operations
force the cache to write dirty lines back to main memory. The ICache then has to be
made coherent with a changed area of memory after any changes to the instructions that
appear at an MVA, and before the new instructions are executed.
On the ARM920T, software is responsible for maintaining coherence between main
memory, the ICache, and the DCache.
Register 7, cache operations register on page 2-17 describes facilities for invalidating
the entire ICache or individual ICache lines, and for cleaning and/or invalidating
DCache lines, or for invalidating the entire DCache.
To clean the entire DCache efficiently, software must loop through each cache entry
using the clean D single entry (using index) operation or the clean and invalidate D
entry (using index) operation. You must perform this using a two-level nested loop
going though each index value for each segment. See DCache organization on
page 4-13.
Example 4-4 shows an example loop for two alternative DCache cleaning operations.
Example 4-4 DCache cleaning loop
for seg = 0 to 7
for index = 0 to 63
Rd = {seg,index}
MCR p15,0,Rd,c7,c10,2
; Clean DCache single
; entry (using index)
or
MCR p15,0,Rd,c7,c14,2
; Clean and Invalidate
; DCache single entry
; (using index)
next index
next seg
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
4-17
Caches, Write Buffer, and Physical Address TAG (PA TAG) RAM
DCache, ICache, and memory coherence is generally achieved by:
•
cleaning the DCache to ensure memory is up to date with all changes
•
invalidating the ICache to ensure that the ICache is forced to re-fetch instructions
from memory.
Software can minimize the performance penalties of cleaning and invalidating caches
by:
•
Cleaning only small portions of the DCache when only a small area of memory
has to be made coherent, for example, when updating an exception vector entry.
Use Clean DCache single entry (using MVA) or Clean and Invalidate DCache
single entry (using MVA).
•
Invalidating only small portions of the ICache when only a small number of
instructions are modified, for example, when updating an exception vector entry.
Use Invalidate ICache single entry (using MVA).
•
Not invalidating the ICache in situations where it is known that the modified area
of memory cannot be in the cache, for example, when mapping a new page into
the currently running process.
Situations that necessitate cache cleaning and invalidating include:
•
4-18
Writing instructions to a cachable area of memory using STR or STM instructions,
for example:
—
self-modifying code
—
JIT compilation
—
copying code from another location
—
downloading code using the EmbeddedICE JTAG debug features
—
updating an exception vector entry.
•
Another bus master, such as a DMA controller, modifying a cachable area main
memory.
•
Turning the MMU on or off.
•
Changing the virtual-to-physical mappings, or Ctt, or Btt, or protection
information, in the MMU page tables. The DCache must be cleaned, and both
caches invalidated, before the cache and write buffer configuration of an area of
memory is changed by modifying Ctt or Btt in the MMU translation table
descriptor. This is not necessary if it is known that the caches cannot contain any
entries from the area of memory whose translation table descriptor is being
modified.
•
Turning the ICache or DCache on, if its contents are no longer coherent.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Caches, Write Buffer, and Physical Address TAG (PA TAG)
Changing the FCSE PID in CP15 register 13 does not change the contents of the cache
or memory, and does not affect the mapping between cache entries and physical
memory locations. It only changes the mapping between ARM9TDMI addresses and
cache entries. This means that changing the FCSE PID does not lead to any coherency
issues. No cache cleaning or cache invalidation is required when the FCSE PID is
changed.
The software design must also consider that the pipelined design of the ARM9TDMI
core means that it fetches three instructions ahead of the current execution point. So, for
example, the three instructions following an MCR that invalidates the ICache, have
already been read from the ICache before it is invalidated.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
4-19
Caches, Write Buffer, and Physical Address TAG (PA TAG) RAM
4.5
Cache cleaning when lockdown is in use
The Clean DCache single entry (using index) and Clean and Invalidate DCache entry
(using index) operations can leave the victim pointer set to the index value used by the
operation. In some circumstances, if DCache locking is in use, this can leave the victim
pointer in the locked region, leading to locked data being evicted from the cache. You
can move the victim pointer outside the locked region by implementing the cache loop,
enclosed by the reading and writing of the base and victim pointer:
MRC p15, 0, Rd, c9, c0, 0
; Read D Cache Base into Rd
Index Clean or Index Clean and Invalidate loops
MCR p15, 0, Rd, c9, c0, 0
; Write D Cache Base and Victim from Rd
Clean DCache single entry (using MVA) and Clean and Invalidate DCache entry (using
MVA) operations do not move the victim pointer, so you do not have to reposition the
victim pointer after using these operations.
4-20
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Caches, Write Buffer, and Physical Address TAG (PA TAG)
4.6
Implementation notes
This section describes the behavior of the ARM920T implementation in areas that are
architecturally unpredictable. For portability to other ARM implementations, software
must not depend on this behavior.
A read from a noncachable (NCB or NCNB) region that unexpectedly hits in the cache
still reads the required data from the AMBA ASB interface. The contents of the cache
are ignored, and the cache contents are not modified. This includes the read portion of
a swap (SWP or SWPB) instruction.
A write to a noncachable (NCB or NCNB) region that unexpectedly hits in the cache
updates the cache and still causes an access on the AMBA ASB interface. This includes
the write portion of a swap instruction.
There are two test interfaces to both the DCache and ICache:
•
debug interface
•
AMBA test interface.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
4-21
Caches, Write Buffer, and Physical Address TAG (PA TAG) RAM
4.7
Physical address TAG RAM
The ARM920T implements a Physical Address (PA) TAG RAM in order to perform
write-backs from the DCache.
A write-back occurs when dirty data, that is about to be overwritten by linefill data,
comes from a memory region that is marked as a write-back region. This data is written
back to main memory to maintain memory coherency.
Note
Dirty data is data that has been modified in the cache, but not updated in main memory.
When a line is written into the data cache, the PA TAG is written into the PA TAG RAM.
If this line has to be written back to main memory, the PA TAG RAM is read and the
physical address is used by the AMBA ASB interface to perform the write-back.
The PA TAG RAM array for a 16KB DCache comprises eight segments x 64 rows per
segment x 26 bits per row. There are two test interfaces to the PA TAG RAM:
4-22
•
debug interface, see Scan chain 4 - debug access to the PA TAG RAM on
page 9-39
•
AMBA test interface, see PA TAG RAM test on page 11-12.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Caches, Write Buffer, and Physical Address TAG (PA TAG)
4.8
Drain write buffer
You can drain the write buffer under software control, so that further instructions are not
executed until the write buffer is drained, using the following methods:
•
store to nonbufferable memory
•
load from noncachable memory
MCR drain write buffer:
•
MCR
p15,0,Rd,c7,c10,4
The write buffer is also drained before performing the following less controllable
activities, which you must consider as implementation-defined:
•
fetch from noncachable memory
•
DCache linefill
•
ICache linefill.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
4-23
Caches, Write Buffer, and Physical Address TAG (PA TAG) RAM
4.9
Wait for interrupt
You can place the ARM920T into a low power state by executing the CP15 MCR wait for
interrupt:
MCR
p15,0,Rd,c7,c0,4
Execution of this MCR causes the write buffer to drain and the ARM920T is put into a
state where it will resume execution of code after either an interrupt or a debug request.
When the interrupt occurs the MCR instruction completes and the FIQ or IRQ handler is
entered as normal. The return link in R14_fiq or R14_irq contains the address of the MCR
instruction plus 8, so that the normal instruction used for interrupt return returns to the
instruction following the MCR:
SUBS
4-24
pc,r14,#4
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Chapter 5
Clock Modes
This chapter describes the different clocking modes available on the ARM920T
processor. It contains the following sections:
•
About ARM920T clocking on page 5-2
•
FastBus mode on page 5-3
•
Synchronous mode on page 5-4
•
Asynchronous mode on page 5-6.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
5-1
Clock Modes
5.1
About ARM920T clocking
The ARM920T processor has two functional clock inputs, BCLK and FCLK.
Internally, the ARM920T is clocked by GCLK. This can be seen on the CPCLK output
as shown in Figure 5-1. GCLK can be sourced from either BCLK or FCLK depending
on the clocking mode, selected using nF bit and iA bit in CP15 register 1 (see Register
1, control register on page 2-12), and external memory access. The three clocking
modes are:
•
FastBus mode on page 5-3
•
Synchronous mode on page 5-4
•
Asynchronous mode on page 5-6.
The ARM920T is a static design and you can stop both clocks indefinitely without loss
of state. Figure 5-1 shows that some of the ARM920T macrocell signals have timing
specified with relation to GCLK. This can be either FCLK or BCLK depending on the
clocking mode.
BCLK
ASB
CPCLK
AMBA
Bus
Interface
GCLK
ARM920T I/O
Rest of ARM920T
nF,iA
FCLK
Figure 5-1 ARM920T clocking
5-2
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Clock Modes
5.2
FastBus mode
In FastBus mode GCLK is sourced from BCLK. The FCLK input is ignored. This
means that BCLK is used to control the AMBA ASB interface and the internal
ARM920T processor core.
On reset, the ARM920T is put into FastBus mode and operates using BCLK. A typical
use for FastBus mode is to execute startup code while configuring a PLL under software
control to produce FCLK at a higher frequency. When the PLL has stabilized and
locked, you can switch the ARM920T to synchronous or asynchronous clocking using
FCLK for normal operation.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
5-3
Clock Modes
5.3
Synchronous mode
In this mode of operation GCLK is sourced from BCLK or FCLK. There are three
restrictions that apply to BCLK and FCLK:
•
FCLK must have a higher frequency than BCLK
•
FCLK must be an integer multiple of the BCLK frequency
•
FCLK must be HIGH whenever there is a BCLK transition.
BCLK is used to control the AMBA ASB interface, and FCLK is used to control the
internal ARM920T processor core. When an external memory access is required the
core either continues to clock using FCLK or is switched to BCLK, as shown in
Table 5-1. This is the same as for asynchronous mode.
Table 5-1 Clock selection for external memory accesses
External memory access operation
GCLK =
Buffered write
FCLK
Nonbuffered write
BCLK
Page walk, cachable read (linefill), noncachable read
BCLK
The penalty in switching from FCLK to BCLK and from BCLK to FCLK is
symmetric, from zero to one phase of the clock to which the core is re-synchronizing.
That is, switching from FCLK to BCLK has a penalty of between zero and one BCLK
phase, and switching back from BCLK to FCLK has a penalty of between zero and one
FCLK phase.
Figure 5-2 on page 5-5 shows an example zero BCLK phase delay when switching
from FCLK to BCLK in synchronous mode.
5-4
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Clock Modes
BCLK
FCLK
FnB
CPCLK
Figure 5-2 Synchronous mode FCLK to BCLK zero phase delay
Figure 5-3 shows an example one BCLK phase delay when switching from FCLK to
BCLK in synchronous mode.
BCLK
FCLK
FnB
CPCLK
Figure 5-3 Synchronous mode FCLK to BCLK one phase delay
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
5-5
Clock Modes
5.4
Asynchronous mode
In this mode of operation GCLK is sourced from BCLK or FCLK. FCLK and BCLK
can be completely asynchronous to one another, with the one restriction that FCLK
must have a higher frequency than BCLK.
BCLK is used to control the AMBA ASB interface, and FCLK is used to control the
internal ARM920T processor core. When an external memory access is required the
core either continues to clock using FCLK or is switched to BCLK. This is the same
as for synchronous mode.The penalty in switching from FCLK to BCLK and from
BCLK to FCLK is symmetric, from zero to one cycle of the clock to which the core is
re-synchronizing. That is, switching from FCLK to BCLK has a penalty of between
zero and one BCLK cycle, and switching back from BCLK to FCLK has a penalty of
between zero and one FCLK cycle.
Figure 5-4 shows an example zero BCLK cycle delay when switching from FCLK to
BCLK in asynchronous mode.
BCLK
FCLK
FnB
CPCLK
Figure 5-4 Asynchronous mode FCLK to BCLK zero cycle delay
Figure 5-5 on page 5-7 shows an example one BCLK cycle delay when switching from
FCLK to BCLK in asynchronous mode.
5-6
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Clock Modes
BCLK
FCLK
FnB
CPCLK
Figure 5-5 Asynchronous mode FCLK to BCLK one cycle delay
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
5-7
Clock Modes
5-8
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Chapter 6
Bus Interface Unit
This chapter describes the ARM920T bus interface. It contains the following sections:
•
About the ARM920T bus interface on page 6-2
•
Unidirectional AMBA ASB interface on page 6-3
•
Fully-compliant AMBA ASB interface on page 6-5
•
AMBA AHB interface on page 6-21
•
Level 2 cache support and performance analysis on page 6-23.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
6-1
Bus Interface Unit
6.1
About the ARM920T bus interface
The AMBA Specification (Rev 2.0) defines two high-performance system buses:
•
the Advanced High-performance Bus (AHB)
•
the Advanced System Bus (ASB).
The ARM920T processor has been designed with a unidirectional ASB interface, plus
the necessary extra control signals to enable efficient implementation of both the AHB
and ASB interface. With no additional logic, you can use the unidirectional ASB
interface in single master systems where the ARM920T is the master. With the addition
of tristate drivers, the ARM920T implements a full ASB interface, either as an ASB bus
master, or as a slave for production test. With the addition of a synthesizable wrapper,
the ARM920T implements a full AHB interface, either as an AHB bus master, or as a
slave for production test.
The wrapper introduces no speed penalties, no performance penalties on reads, no
performance penalties on buffered writes, and minimal performance penalty on
nonbuffered writes. The MCR drain write buffer requires an additional instruction to
operate in a predictable manner. See AMBA AHB interface on page 6-21 for details.
In this section the following abbreviations are used:
NCNB
Noncachable and nonbufferable
NCB
Noncachable and bufferable
NC
Noncachable
WT
Cachable and write-through
WB
Cachable and write-back.
6-2
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Bus Interface Unit
6.2
Unidirectional AMBA ASB interface
The AMBA Specification (Rev 2.0) defines the Advanced Microcontroller Bus
Architecture (AMBA) ASB interface for use with multiple masters. This requires that
only the granted master controls and drives the bus system. The unidirectional AMBA
ASB interface on the ARM920T supplies the constituent signals to make a bidirectional
interface, that is input, output, and output enable. These signals are shown in Table 6-1.
Table 6-1 Relationship between bidirectional and unidirectional ASB interface
ARM DDI 0151C
ASB signal
ARM920T input
ARM920T output
ARM920T output enable
AGNTx
AGNT
-
-
AREQx
-
AREQ
-
BCLK
BCLK
-
-
BnRES
BnRES
-
-
DSELx
DSEL
-
-
BA[31:12]
-
AOUT[31:12]
ENBA
BA[11:2]
AIN[11:2]
AOUT[31:0]
ENBA
BA[1:0]
-
AOUT[1:0]
ENBA
BLOK
-
LOK
ENBA
BPROT[1:0]
-
PROT[1:0]
ENBA
BSIZE[1:0]
-
SIZE[1:0]
ENBA
BWRITE
WRITEIN
WRITEOUT
ENBA
BD[31:0]
DIN[31:0]
DOUT[31:0]
ENBD
BTRAN[1:0]
-
TRAN[1:0]
ENBTRAN
BERROR
ERRORIN
ERROROUT
ENSR
BLAST
LASTIN
LASTOUT
ENSR
BWAIT
WAITIN
WAITOUT
ENSR
Copyright © 2000, 2001 ARM Limited. All rights reserved.
6-3
Bus Interface Unit
An ASB bus cycle is defined from falling-edge to falling-edge transition of BCLK. The
LOW part is referred to as phase 1, the HIGH part as phase 2. The timing is shown in
Table 6-2, and is for reference only. It is assumed that the ARM920T macrocell is used
in either an AMBA ASB or AMBA AHB system.
Table 6-2 ARM920T input/output timing
ARM920T
input
Timing
ARM920T
output
Timing
-
-
AREQ
Change phase 2
AGNT
Setup to rising BCLK
-
-
DSEL
Setup to falling BCLK
-
-
AIN[11:2]
Setup to falling BCLK
AOUT[31:0]
Change phase 2
-
-
LOK
Change phase 2
-
-
BPROT[1:0]
Change phase 2
-
-
SIZE[1:0]
Change phase 2
WRITEIN
Setup to falling BCLK
WRITEOUT
Change phase 2
DIN[31:0]
Setup to falling BCLK
DOUT[31:0]
Change phase 1
-
-
TRAN[1:0]
Change phase 2 (1)
ERRORIN
Setup to rising BCLK
ERROROUT
Fixed to 0
LASTIN
Setup to rising BCLK
LASTOUT
Fixed to 0
WAITIN
Setup to rising BCLK
WAITOUT
Change phase 1
The timing for TRAN[1:0] is slightly different, so that if the ARM920T loses the GNT
signal, TRAN[1:0] is changed to indicate A-TRAN in the same phase 1. Under these
circumstances however, the ARM920T does not drive BTRAN[1:0] in the subsequent
phase 2.
6-4
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Bus Interface Unit
6.3
Fully-compliant AMBA ASB interface
AMBA Specification (Rev 2.0), defines the AMBA ASB interface for use with multiple
masters. Connecting the unidirectional ARM920T signals as indicated in Connecting
the ARM920T to an AMBA ASB interface implements a fully-compliant interface, either
as an ASB bus master, or slave for production test. For details of how the AMBA ASB
interface operates, refer to the AMBA Specification (Rev 2.0).
6.3.1
Connecting the ARM920T to an AMBA ASB interface
For bidirectional signals, BA[11:2], BWRITE, BD[31:0], BERROR, BWAIT, and
BLAST, the macrocell outputs must be tristate buffered, using the output enable
specified in Table 6-1 on page 6-3. The ARM920T macrocell outputs are continuously
driven and intended to drive the signals to the edge of the macrocell from where they
can be buffered for additional routing and tristate behavior. The drive strength chosen
for tristate drivers must be governed by the ASB load. Figure 6-1 shows the required
output buffer for bidirectional signals.
ARM920T output enable
ASB signal
ARM920T output
ARM920T input
Figure 6-1 Output buffer for bidirectional signals
For output signals, BA[31:12], BA[1:0], BLOK, BPROT[1:0], BSIZE[1:0], and
BTRAN[1:0], the macrocell outputs must be tristate buffered, using the output enable
specified in Table 6-1 on page 6-3. The drive strength chosen for tristate drivers must
be governed by the ASB load. Figure 6-2 on page 6-6 shows the output buffer required
for unidirectional signals.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
6-5
Bus Interface Unit
ARM920T output enable
ASB signal
ARM920T output
Figure 6-2 Output buffer for unidirectional signals
You can connect the input signals, AGNTx, BCLK, BnRES, and DSELx directly to
the ARM920T. The signals are appropriately buffered when the signal reaches the edge
of the macrocell so additional buffering is not required. The output signal AREQ must
be buffered with no tristate control, and is dependent on the load within the ASB system.
6.3.2
Transfer types
The AMBA ASB specification describes three transfer types that are encoded in
BTRAN[1:0]. Table 6-3 shows these transfer types.
Table 6-3 AMBA ASB transfer types
BTRAN[1:0]
Transfer type
Description
00
Address-only
(A-TRAN)
Used when no data movement is required. The three
main uses for address-only transfers are:
•
for IDLE cycles
•
for bus handover cycles
•
for speculative address decoding without
committing to a data transfer.
01
-
Reserved.
10
Nonsequential
(N-TRAN)
Used for single transfers or the first transfer of a burst.
The address of the transfer is unrelated to the previous
bus access.
11
Sequential
(S-TRAN)
Used for successive transfers in burst. The address of a
SEQUENTIAL transfer is always related to the
previous transfer.
The ARM920T does not use N-TRAN cycles, instead it uses an A-TRAN cycle
followed by a S-TRAN cycle for nonsequential transfers. This eases AMBA decoder
design considerably, particularly for high-speed designs.
6-6
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Bus Interface Unit
The output signals ASTB, BURST[1:0], and NCMAHB have been added to the
ARM920T bus interface. They are necessary to support the AMBA AHB wrapper, but
can also be used to provide optimized accesses in an AMBA ASB system:
ASTB
This signal distinguishes between an IDLE cycle and the A-TRAN cycle
of a nonsequential transfer. It is asserted with the same timing as
AOUT[31:0], changing in phase 2. Usually a memory controller only
commits to a transfer when it sees the S-TRAN cycle, perhaps only
decoding the address during the A-TRAN cycle. ASTB is asserted in the
preceding A-TRAN cycle, indicating that the current A-TRAN is
followed by an S-TRAN, providing AGNT is HIGH on the next rising
edge of BCLK.
BURST[1:0] This signal gives an indication of the length of a sequential burst, as
shown in Table 6-4.
Table 6-4 Burst transfers
BURST[1:0]
Transfer
00
No burst or undefined burst
length
01
4-word burst
10
8-word burst
11
No burst or undefined burst
length
For linefills, BURST[1:0] indicates 8 words. For cache line evictions,
BURST[1:0] indicates either 4 or 8 words. For all other transfers,
BURST[1:0] indicates no burst or undefined burst length.
The meaning of the BURST[1:0] encoding is clarified when considered
whether the transfer is a read or write. In this way you can distinguish
between bufferable and nonbufferable STR/STM and table walks, as shown
in Table 6-5 on page 6-8.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
6-7
Bus Interface Unit
Table 6-5 Use of WRITEOUT signal
BURST[1:0]
WRITEOUT
ARM920T bus access
Type
00
Read
NC LDR/LDM/fetch
Noncachable read
00
Write
NCNB STR/STM
Nonbufferable write
01
Read
-
-
01
Write
Write-back of 4 words
Bufferable write
10
Read
Linefill of 8 words
Cachable read
10
Write
Write-back of 8 words
Bufferable write
11
Read
Table walk
Cachable read
11
Write
NCB/WT/WB miss STR/STM
Bufferable write
The BURST[1:0] signals change in phase 2 and are asserted in the phase
when ASTB is asserted. BURST[1:0] then remains unchanged until the
next transfer.
NCMAHB
This signal indicates for noncached load multiples whether more words
are requested as part of the current burst transfer. When HIGH this
indicates more words are requested. When LOW, on the last S-TRAN of
the burst, this indicates that the current transfer is the last word of the
burst. It is asserted in phase 2 and is only valid if AGNT remains asserted
throughout the transfer.
The following timing diagrams show the types of transfer that can be initiated by the
ARM920T rev1:
•
Instruction fetch after reset on page 6-11
•
Example LDR from address 0x108 on page 6-12
•
Example LDM of 5 words from 0x108 on page 6-13
•
Example nonbuffered STR on page 6-14
•
Example nonbuffered STM on page 6-15
•
Example linefill from 0x100 on page 6-16
•
Example 4-word data eviction on page 6-17
•
Example swap operation on page 6-19.
6-8
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Bus Interface Unit
Where the AREQ and AGNT signals and the responses from the ASB slave are not
shown in these diagrams, it is assumed that AGNT is asserted and the ASB slave
response is DONE.
Different slave responses and bus master handover are covered in the AMBA
Specification (Rev 2.0). It is assumed that you are using the ARM920T macrocell within
a multi-master ASB system, so unidirectional ASB timing diagrams are not provided.
6.3.3
Instruction fetch after reset
The general operation of the AMBA ASB during reset is described in the AMBA
Specification (Rev 2.0). The reset signal, BnRES, is active LOW, and can be asserted
asynchronously to guarantee the bus is in a safe state. During reset, the following
actions occur on the bus:
•
The arbiter grants the default bus master.
•
The default bus master must:
— drive BTRAN to indicate an ADDRESS-ONLY transfer
— drive BLOK LOW to allow arbitration
— drive BA, BWRITE, BSIZE, and BPROT to any value
— tristate BD.
•
All other bus masters must tristate shared bus signals, BA, BD, BWRITE,
BTRAN, BSIZE, BPROT, and BLOK.
•
The decoder must:
•
—
deassert all slave select signals, DSELx
—
provide the appropriate transfer response.
All slaves must tristate shared bus signals.
You must hold BnRES LOW for a minimum of five BCLK cycles to ensure complete
reset of the ARM920T processor. You must deassert BnRES during the BCLK LOW
phase.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
6-9
Bus Interface Unit
Figure 6-3 on page 6-11 shows the default bus master during reset to be the TIC
controller. After reset, the ARM920T processor is made the default bus master, so there
is a handover phase when BA, BWRITE, BSIZE, BPROT, and BLOK are not driven,
but BTRAN is driven with ADDRESS-ONLY. The ARM920T processor continues as
the default bus master without requesting the bus, so it must:
•
drive BTRAN to indicate an ADDRESS-ONLY transfer
•
drive BLOK LOW to allow arbitration
•
drive BA, BWRITE, BSIZE, and BPROT to any value
•
tristate BD.
The ARM920T processor then requests use of the bus and, because it is already granted
the bus, starts the first ADDRESS-ONLY cycle that is not an IDLE cycle, indicated by
ASTB. The first instruction fetch continues from then.
6-10
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Bus Interface Unit
BnRES
BCLK
Bus handover
BA[31:0]
0x0
0x4
BD[31:0]
Word 0
Word 1
BWRITE
BTRAN[1:0]
A-TRAN
A-TRAN
A-TRAN
A-TRAN
A-TRAN
A-TRAN
A-TRAN
S-TRAN
BPROT[1:0]
10
BURST[1:0]
00
A-TRAN
A-TRAN
A-TRAN
A-TRAN
S-TRAN
A-TRAN
ASTB
NCMAHB
AGNTARM
AGNTTIC
AREQARM
Figure 6-3 Instruction fetch after reset
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
6-11
Bus Interface Unit
6.3.4
Noncached LDRs and noncached fetches
The only difference between these noncached LDRs and noncached fetches is the
BPROT[1:0] information, as shown in Table 6-6.
Table 6-6 Noncached LDR and fetch
BPROT[0]
Transfer
0
Opcode fetch
1
Data access
The address is word-aligned for an LDR and fetch. An example LDR is shown in
Figure 6-4.
BCLK
BA[31:0]
0x108
BD[31:0]
Word 1
BWRITE
BTRAN[1:0]
A-TRAN
S-TRAN
A-TRAN
BPROT[1:0]
11 or 01 for LDR
10 or 00 for fetch
BURST[1:0]
00 = No burst or undefined burst length
ASTB
NCMAHB
Figure 6-4 Example LDR from address 0x108
6-12
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Bus Interface Unit
6.3.5
Noncached LDM
For a noncached LDM the BURST[1:0] information is always 00 = No burst or undefined
burst length, though the NCMAHB signal gives one cycle advance warning of the end
of the burst transfer if AGNT remains asserted throughout the burst transfer. The
address is word-aligned. An example LDM is shown in Figure 6-5.
BCLK
BA[31:0]
0x108
BD[31:0]
0x108
0x104
0x110
0x10C
1
2
3
4
5
S-TRAN
S-TRAN
S-TRAN
S-TRAN
A-TRAN
BWRITE
BTRAN[1:0]
A-TRAN
S-TRAN
BPROT[1:0]
11 or 01 for data access, 10 or 00 for opcode fetch
BURST[1:0]
00 = No burst or undefined burst length
ASTB
NCMAHB
Figure 6-5 Example LDM of 5 words from 0x108
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
6-13
Bus Interface Unit
6.3.6
Buffered and nonbuffered STR
For a buffered or nonbuffered STR the BURST[1:0] information is:
11
Buffered STR, no burst or undefined burst length.
00
Nonbuffered STR, no burst or undefined burst length.
The address is word-aligned. An example STR is shown in Figure 6-6.
BCLK
BA[31:0]
0x108
BD[31:0]
1
BWRITE
BTRAN[1:0]
A-TRAN
S-TRAN
BPROT[1:0]
11 or 01
BURST[1:0]
00 = No burst or undefined burst length
A-TRAN
ASTB
NCMAHB
Figure 6-6 Example nonbuffered STR
6-14
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Bus Interface Unit
6.3.7
Buffered and nonbuffered STM
For a buffered or nonbuffered STM the BURST[1:0] information is:
11
Buffered STM, no burst or undefined burst length.
00
Nonbuffered STM, no burst or undefined burst length.
The address is word-aligned. An example nonbuffered STM is shown in Figure 6-7.
BCLK
BA[31:0]
0x108
BD[31:0]
0x110
0x10C
0x118
0x114
1
2
3
4
5
S-TRAN
S-TRAN
S-TRAN
S-TRAN
A-TRAN
BWRITE
BTRAN[1:0]
A-TRAN
S-TRAN
BPROT[1:0]
11 or 01
BURST[1:0]
00 = No burst or undefined burst length
ASTB
NCMAHB
Figure 6-7 Example nonbuffered STM
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
6-15
Bus Interface Unit
6.3.8
Cached LDR, cached LDM, and cached fetch
A cached LDR or LDM, and a cached fetch, are equivalent to a linefill operation. The
BURST[1:0] information is always 10 = 8 words. The address is word-aligned and
increases from the lowest address. The lowest five bits always increase from 0x00 to
0x1C. An example linefill is shown in Figure 6-8.
BCLK
BA[31:0]
0x100
BD[31:0]
0x108
0x104
0x110
0x10C
0x118
0x114
0x11C
1
2
3
4
5
6
7
8
S-TRAN
S-TRAN
S-TRAN
S-TRAN
S-TRAN
S-TRAN
S-TRAN
A-TRAN
BWRITE
BTRAN[1:0]
A-TRAN
S-TRAN
BPROT[1:0]
11 or 01 for data access, 10 or 00 for opcode fetch
BURST[1:0]
10 = 8 words
ASTB
NCMAHB
Figure 6-8 Example linefill from 0x100
6-16
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Bus Interface Unit
6.3.9
Dirty data eviction, write-back of 4 or 8 words
Dirty data can be evicted from a cache line as either the first four words, the last four
words, or all eight words of the cache line. The address is word-aligned and increases
from the lowest address. BPROT[1:0] is always 11, indicating privileged data access.
Figure 6-9 shows an example four-word dirty data eviction of the second half of a cache
line.
BCLK
BA[31:0]
0x110
0x118
0x114
BD[31:0]
1
0x11C
2
3
4
S-TRAN
S-TRAN
A-TRAN
BWRITE
BTRAN[1:0]
A-TRAN
S-TRAN
S-TRAN
BPROT[1:0]
11
BURST[1:0]
01 = 4 words
ASTB
NCMAHB
Figure 6-9 Example 4-word data eviction
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
6-17
Bus Interface Unit
The allowable combinations are listed in Table 6-7.
Table 6-7 Data eviction of 4 or 8 words
6.3.10
Data evicted
BURST[1:0]
Lowest 5 bits of the address
First 4 words
01
0x00 to 0x0C
Last 4 words
01
0x10 to 0x1C
All 8 words
10
0x00 to 0x1C
Swap
The swap operation is implemented as a single read transfer followed by a single write
transfer. The BLOK signal is asserted so that the write transfer is locked to the
preceding read transfer. This must be used by the arbiter to ensure that no other bus
master is given access to the bus between the read and write transfers. An example swap
operation is shown in Figure 6-10 on page 6-19.
6-18
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Bus Interface Unit
BCLK
BA[31:0]
BD[31:0]
Read
Write
BWRITE
BTRAN[1:0]
A-TRAN
BPROT[1:0]
S-TRAN
A-TRAN
A-TRAN
A-TRAN
A-TRAN
S-TRAN
A-TRAN
11 or 01
BLOK
BURST[1:0]
00 = No burst or undefined burst length
ASTB
NCMAHB
AREQ
AGNT
Figure 6-10 Example swap operation
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
6-19
Bus Interface Unit
6.3.11
Page walk
A page walk is identical to a noncached LDR on the ASB. That is, a single word read.
The BURST[1:0] encoding is always 11. For a page walk caused by an opcode fetch,
BPROT[1:0] = 10. For a page walk caused by a data operation, BPROT[1:0] = 11. The
page walk is always privileged.
6.3.12
AMBA ASB slave transfers
You can test the ARM920T processor as an individual module within an AMBA system,
responding only to transfers from the AMBA ASB. In this mode of operation the
ARM920T processor is never granted the ASB as a bus master, and responds as an ASB
slave, detecting the assertion of DSEL. This is described in detail in the AMBA
Specification (Rev 2.0).
6-20
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Bus Interface Unit
6.4
AMBA AHB interface
The AMBA Specification (Rev 2.0) defines the AMBA AHB interface for use with
multiple masters. With the addition of a synthesizable wrapper, the ARM920T
implements a full AHB interface, either as an AHB bus master, or as a slave for
production test. This is delivered as synthesizable RTL, with synthesis scripts. Contact
ARM for details of how to obtain this information. The interface uses ASTB,
BURST[1:0], and NCMAHB signals in addition to the unidirectional ASB signals.
This allows an efficient implementation that has:
•
no speed penalty
•
no cycle penalties for read transfers
•
no cycle penalties for buffered write transfers
•
one cycle penalty for every nonbuffered write transfer
•
swaps incur one cycle penalty on the read transfer and one cycle penalty on the
write transfer
•
the MCR drain write buffer instruction, MCR p15, 0, Rd, c7, c10, 4, drains the write
buffer to the AHB wrapper.
In the case of the MCR drain write buffer the write transfers appear as buffered, so the
ARM920T processor continues execution before the last write transfer is completed on
the AHB.
An example of how this might be a problem is if the last STR to the write buffer was to
clear an interrupt source prior to enabling interrupts to the ARM9TDMI, then the
following sequence might result in an interrupt being returned to the ARM9TDMI
before the interrupt is cleared:
Buffered STR to clear interrupt
MCR drain write buffer
Enable interrupts.
There are three solutions:
1.
For a non write-sensitive address. Issue the STR twice. The first STR completes
before the second STR enters the AHB wrapper, guaranteeing the interrupt is
cleared before the interrupts are enabled:
Buffered STR to clear interrupt
Buffered STR to clear interrupt
MCR drain write buffer
Enable interrupts.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
6-21
Bus Interface Unit
2.
For a write-sensitive address. Issue any other buffered STR to a non write-sensitive
address. This must be to a NCB or WT region to ensure the STR is committed to
the write buffer:
Buffered STR to clear interrupt
Buffered STR to a non write-sensitive address
MCR drain write buffer
Enable interrupts.
3.
Issue a read on the AHB before enabling the interrupts. This must be from a
noncachable region to ensure the read appears on the AHB:
Buffered STR to clear interrupt
MCR drain write buffer
Non-cachable LDR or fetch
Enable interrupts.
6-22
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Bus Interface Unit
6.5
Level 2 cache support and performance analysis
The BURST[1:0] encoding, used with WRITEOUT and PROT[1:0], or BWRITE
and BPROT[1:0], is intended to provide the information necessary to implement an
efficient AHB wrapper. However, it also provides enough information for a level 2
cache to be implemented outside the ARM920T macrocell. Contact ARM for details.
Encodings for the range of accesses supported by the ARM920T processor are listed in
Table 6-8.
Table 6-8 ARM920T supported bus access types
BURST[1:0]
WRITEOUT
PROT[0]
ARM920T bus access
00
Read
0
Noncachable fetch
00
Read
1
Noncachable LDR or LDM
00
Write
0
-
00
Write
1
Nonbuffered STR or STM
01
Read
0
-
01
Read
1
-
01
Write
0
-
01
Write
1
Write-back of 4 words
10
Read
0
Instruction linefill of 8 words
10
Read
1
Data linefill of 8 words
10
Write
0
-
10
Write
1
Write-back of 8 words
11
Read
0
Instruction table walk
11
Read
1
Data table walk
11
Write
0
-
11
Write
1
Buffered STR or STM
By monitoring the AMBA ASB bus transfers, qualified by the ARM920T AGNT and
slave responses BERROR, BLAST, and BWAIT, you can implement a performance
monitor outside the ARM920T macrocell. This might give the type of information
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
6-23
Bus Interface Unit
shown in Example 6-1 on page 6-24 after running a program. The performance monitor
can be made accessible as a memory mapped peripheral or using JTAG on the
ARM920T external scan chain.
Example 6-1 Typical output data from a performance monitor
I TLB Page Table Walks
D TLB Page Table Walks
4 Word Writebacks
8 Word Writebacks
I Cache Linefills
D Cache Linefills
NC Loads
NC Fetches
NCNB Stores
NCB, WT or WB Miss Stores
BCLK Cycles
6-24
:
:
:
:
:
:
:
:
:
:
:
1
1
10
5
48
28
2
38
2
13
1594
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Chapter 7
Coprocessor Interface
This chapter describes the ARM920T coprocessor interface. It contains the following
sections:
•
About the ARM920T coprocessor interface on page 7-2
•
LDC/STC on page 7-5
•
MCR/MRC on page 7-9
•
Interlocked MCR on page 7-11
•
CDP on page 7-13
•
Privileged instructions on page 7-15
•
Busy-waiting and interrupts on page 7-17.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
7-1
Coprocessor Interface
7.1
About the ARM920T coprocessor interface
The ARM920T processor supports the connection of on-chip coprocessors through an
external coprocessor interface. All types of coprocessor instruction are supported.
The ARM920T coprocessor interface allows you to attach specially designed
coprocessor hardware to the ARM920T. Example uses include:
7.1.1
•
attachment of accelerators for floating-point math, DSP, 3-D graphics,
encryption, or decryption
•
the ARM instruction set supports the connection of 16 coprocessors, numbered 0
to 15, to an ARM processor.
Internal coprocessors
The ARM920T processor contains two internal coprocessors:
•
CP14 for debug control
•
CP15 for memory system control and test control.
This means that coprocessors attached externally to the ARM920T processor cannot be
assigned coprocessor numbers 15 or 14. Other coprocessor numbers have been
allocated by ARM for internal usage. Contact ARM for a full list of reserved
coprocessor numbers.
The register map of CP15 is described in CP15 register map summary on page 2-5. The
functionality of CP14 is described in Debug communications channel on page 9-64.
7.1.2
External coprocessors
Coprocessors determine the instructions they have to execute by using a pipeline
follower in the coprocessor. As each instruction arrives from memory, it enters both the
ARM pipeline and the coprocessor pipeline. To avoid a critical path for the instruction
being latched by the coprocessor, the coprocessor pipeline must operate one clock phase
behind the ARM920T pipeline. The ARM920T then informs the coprocessor when
instructions move from Decode into Execute, and whether the instruction has to be
executed.
To enable coprocessors to continue doing coprocessor data operations while the
ARM920T pipeline is stalled (for instance waiting for a cache linefill to occur), the
coprocessor must monitor a clock CPCLK, and a clock stall signal nCPWAIT. If
nCPWAIT is LOW on the rising edge of CPCLK, the ARM920T pipeline is stalled
and the coprocessor pipeline must not advance.
7-2
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Coprocessor Interface
Figure 7-1 indicates the timing for these signals and when the coprocessor pipeline
must advance its state. In this diagram, Coproc clock shows the result of ORing
CPCLK with the inverse of nCPWAIT. This is one technique for generating a clock
that reflects the ARM9TDMI pipeline advancing.
Coprocessor
pipeline
CPCLK
nCPWAIT
Coproc
clock
Figure 7-1 ARM920T coprocessor clocking
Coprocessor instructions
There are three classes of coprocessor instructions:
LDC or STC
Load coprocessor register from memory or store coprocessor
register to memory.
MCR or MRC
Register transfer between coprocessor and ARM processor core.
CDP
Coprocessor data operation.
Examples of how a coprocessor must execute these instruction classes are given in:
•
LDC/STC on page 7-5
•
MCR/MRC on page 7-9
•
Interlocked MCR on page 7-11
•
CDP on page 7-13.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
7-3
Coprocessor Interface
7.1.3
Enabling and disabling the external coprocessor interface buses
The ARM920T macrocell has the CPEN input, coprocessor enable.
When tied LOW, the CPID and CPDOUT buses are held stable. When tied HIGH, the
CPID and CPDOUT buses are enabled. This is meant as a power saving feature and is
intended to be used statically within an embedded system.
7-4
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Coprocessor Interface
7.2
LDC/STC
The cycle timing for LDC/STC operations are shown in Figure 7-2.
ARM processor pipeline
Coprocessor pipeline
Decode
Execute
(GO)
Decode
Execute
(GO)
Execute
(GO)
Execute
(GO)
Execute
(GO)
Execute
(LAST)
Execute
(GO)
Memory
Execute
(LAST)
Memory
Write
Write
CPCLK
nCPMREQ
CPID[27:0]
LDC
CPPASS
CPLATECANCEL
CHSDE[1:0]
CHSEX[1:0]
GO
GO
GO
LAST
Ignored
A
A+4
A+8
A+C
CPDOUT[31:0]
LDC/MCR
CPDIN[31:0]
STC/MRC
DnMREQ
(ARM920T
internal)
DMORE
(ARM920T
internal)
DA[31:0]
(ARM920T
internal)
Figure 7-2 ARM920T LDC/STC cycle timing
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
7-5
Coprocessor Interface
In Figure 7-2 on page 7-5, four words of data are transferred. The number of words
transferred is determined by how the coprocessor drives the CHSDE[1:0] and
CHSEX[1:0] buses.
As with all other instructions, the ARM920T processor core performs the main
instruction decode off the rising edge of the clock during the Decode stage. From this,
the ARM9TDMI CPU core commits to executing the instruction, and so performs an
instruction Fetch. The coprocessor instruction pipeline keeps in step with the
ARM920T by monitoring CPMREQ, a latched copy of the ARM9TDMI instruction
memory request signal InMREQ. Whenever nCPMREQ is LOW, an instruction Fetch
is occurring and CPID is updated with the fetched instruction in the next cycle. This
means that the instruction currently on CPID enters the Decode stage of the coprocessor
pipeline, and that the instruction in the Decode stage of the coprocessor pipeline enters
its Execute stage.
During the Execute stage, the condition codes are combined with the flags to determine
whether the instruction can be executed or not. The output CPPASS is asserted (HIGH)
if the instruction in the Execute stage of the coprocessor pipeline:
•
is a coprocessor instruction
•
has passed its condition codes.
If a coprocessor instruction busy-waits, CPPASS is asserted on every cycle until the
coprocessor instruction is executed. If an interrupt occurs during busy-waiting,
CPPASS is driven LOW, and the coprocessor stops execution of the coprocessor
instruction.
Another output, CPLATECANCEL, is used to cancel a coprocessor instruction when
the instruction preceding it caused a Data Abort. This is valid on the rising edge of
CPCLK on the cycle after the first Execute cycle of the coprocessor instructions.
CPLATECANCEL is only asserted during the first Memory cycle of the execution of
coprocessor instructions.
On the falling edge of the clock, the ARM920T processor core examines the
coprocessor handshake signals CHSDE[1:0] or CHSEX[1:0]:
7-6
•
if a new instruction is entering the Execute stage in the next cycle, it examines
CHSDE[1:0]
•
if the coprocessor instruction currently in Execute requires another Execute cycle,
it examines CHSEX[1:0].
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Coprocessor Interface
The handshake signals encode one of four states:
ABSENT
If there is no coprocessor attached that can execute the coprocessor
instruction, the handshake signals indicate the ABSENT state. In this
case, the ARM9TDMI processor core takes the undefined instruction
exception.
WAIT
If there is a coprocessor attached that can execute the instruction but not
immediately, the coprocessor handshake signals must be driven to
indicate that the ARM9TDMI processor core must stall until the
coprocessor can catch up. This is known as the busy-wait condition.
In this case, the ARM9TDMI processor core loops in an IDLE state,
waiting for CHSEX[1:0] to be driven to another state, or for an interrupt
to occur. If CHSEX[1:0] changes to ABSENT, the undefined instruction
exception is taken. If CHSEX[1:0] changes to GO or LAST, the
instruction proceeds as described below.
If an interrupt occurs, the ARM9TDMI processor core is forced out of the
busy-wait state. This is indicated to the coprocessor by the CPPASS
signal going LOW. The instruction is restarted at a later date. Therefore
the coprocessor must not commit to the instruction (change any of the
coprocessor states) until it has seen CPPASS go HIGH, and the
handshake signals indicate the GO or LAST condition.
GO
The GO state indicates that the coprocessor can execute the instruction
immediately, and that it requires another cycle of execution. Both the
ARM9TDMI processor core and the coprocessor must also consider the
state of the CPPASS signal before actually committing to the instruction.
For an LDC or STC instruction, the coprocessor instruction must drive the
handshake signals with GO when two or more words still have to be
transferred. When only one more word is required, the coprocessor must
drive the handshake signals with the LAST condition.
In phase 2 of the Execute stage, the ARM9TDMI processor core outputs
the address for the LDC/STC. Also in this phase, DnMREQ is driven LOW,
indicating to the memory system that a memory access is required at the
data end of the device. The timing for the data on CPDOUT[31:0] for an
LDC, and CPDIN[31:0] for an STC, is as shown in Figure 7-2 on page 7-5.
LAST
ARM DDI 0151C
An LDC or STC can be used for more than one item of data. If this is the
case, possibly after busy waiting, the coprocessor must drive the
coprocessor handshake signals with a number of GO states and, in the
penultimate cycle, with LAST. The LAST indicating that the next
transfer is the final one. If there is only one transfer, the sequence is
[WAIT,[WAIT,...]],LAST.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
7-7
Coprocessor Interface
7.2.1
Coprocessor handshake encoding
Table 7-1 shows how the handshake signals CHSDE[1:0] and CHSEX[1:0] are
encoded.
Table 7-1 Handshake encoding
State
[1:0]
ABSENT
10
WAIT
00
GO
01
LAST
11
If you do not attach a coprocessor to the ARM920T, then the handshake signals must be
driven with ABSENT.
If you attach multiple coprocessors to the interface, the handshaking signals can be
combined by ANDing bit 1, and ORing bit 0. In the case of two coprocessors that have
handshaking signals CHSDE1, CHSEX1 and CHSDE2, CHSEX2 respectively:
CHSDE[1]<= CHSDE1[1] AND CHSDE2[1]
CHSDE[0]<= CHSDE1[0] OR CHSDE2[0]
CHSEX[1]<= CHSEX1[1] AND CHSEX2[1]
CHSEX[0]<= CHSEX1[0] OR CHSEX2[0].
Consequently, if the coprocessor does not recognize a coprocessor instruction, it must
drive CHSDE[1:0] and CHSEX[1:0] with ABSENT.
7-8
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Coprocessor Interface
7.3
MCR/MRC
MCR/MRC cycles look very similar to STC/LDC. An example with a busy-wait state is shown
in Figure 7-3.
ARM processor pipeline
Coprocessor pipeline
Decode
Execute
(WAIT)
Decode
Execute
(LAST)
Execute
(WAIT)
Memory
Execute
(LAST)
Write
Memory
Write
CPCLK
CPID[31:0]
MCR/
MRC
nCPMREQ
CPPASS
CPLATECANCEL
CHSDE[1:0]
CHSEX[1:0]
WAIT
LAST
Ignored
CPDOUT[31:0]
LDC/MCR
CPDIN[31:0]
STC/MRC
Figure 7-3 ARM920T MCR/MRC transfer timing
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
7-9
Coprocessor Interface
In Figure 7-3 on page 7-9, first nCPMREQ is driven LOW to denote that the
instruction on CPID is entering the Decode stage of the pipeline. The coprocessor
decodes the new instruction and drives CHSDE[1:0] as required.
In the next cycle nCPMREQ is driven LOW to denote that the instruction has now been
issued to the Execute stage. If the condition codes pass, and the instruction is to be
executed, the CPPASS signal is driven HIGH and the CHSDE[1:0] handshake bus is
examined (it is ignored in all other cases).
For any successive Execute cycles the CHSEX[1:0] handshake bus is examined. When
the LAST condition is observed, the instruction is committed. In the case of an MCR,
the CPDOUT[31:0] bus is driven with the register data. In the case of an MRC,
CPDIN[31:0] is sampled at the end of the ARM920T Memory stage and written to the
destination register during the next cycle.
For an MCR or MRC, with no busy-wait states, the coprocessor drives CHSDE[1:0] with
LAST. This commits the instruction for execution in the next cycle. The value on
CHSEX[1:0] is ignored.
7-10
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Coprocessor Interface
7.4
Interlocked MCR
If the data for an MCR operation is not available inside the ARM9TDMI pipeline during
its first Decode cycle, the ARM920T pipeline interlocks for one or more cycles until the
data is available. An example of this is where the register being transferred is the
destination from a preceding LDR instruction. In this situation the MCR instruction enters
the Decode stage of the coprocessor pipeline, and remains there for a number of cycles
before entering the Execute stage. Figure 7-4 on page 7-12 gives an example of an
interlocked MCR. In this example the MCR busy-waits the ARM9TDMI. When the
instruction enters the Decode stage of the coprocessor pipeline, the coprocessor drives
CHSDE[1:0] with WAIT. Due to an interlock in the ARM9TDMI, the instruction
remains in Decode for an extra cycle. This is signaled to the coprocessor by nCPMREQ
going HIGH, holding the instruction in the Decode stage of the coprocessor pipeline
follower. The coprocessor signals WAIT to the ARM9TDMI during its second Decode
cycle. The interlock in the ARM9TDMI resolves, nCPMREQ goes LOW, and the
instruction moves from Decode into Execute.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
7-11
Coprocessor Interface
ARM processor pipeline
Coprocessor pipeline
Decode
(interlock)
Decode
Decode
Execute
(WAIT)
Decode
Execute
(LAST)
Execute
(WAIT)
Memory
Execute
(LAST)
Memory
Write
Write
CPCLK
CPID[31:0]
MCR/
MRC
nCPMREQ
CPPASS
CPLATECANCEL
CHSDE[1:0]
CHSEX[1:0]
WAIT/
Ignored
WAIT
LAST
Ignored
CPDOUT[31:0]
LDC/MCR
CPDIN[31:0]
STC/MRC
Figure 7-4 ARM920T interlocked MCR
7-12
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Coprocessor Interface
7.5
CDP
CDPs normally execute in a single cycle. Like all other instructions, nCPMREQ is
driven LOW to signal when an instruction is entering the Decode and then the Execute
stage of the pipeline:
•
if the instruction is to be executed, the CPPASS signal is driven HIGH during
phase 2 of the Execute stage
•
if the coprocessor can execute the instruction immediately it drives CHSDE[1:0]
with LAST
•
if the instruction requires a busy-wait cycle, the coprocessor drives CHSDE[1:0]
with WAIT and then CHSEX[1:0] with LAST.
Figure 7-5 on page 7-14 shows a CDP that is canceled due to the previous instruction
causing a Data Abort. The CDP instruction enters the Execute stage of the pipeline, and
is signaled to execute by CPPASS. In the following phase CPLATECANCEL is
asserted. This causes the coprocessor to terminate execution of the CDP instruction, and
for it to cause no state changes to the coprocessor.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
7-13
Coprocessor Interface
LDR with Data Abort
Execute
Memory
CDP: ARM processor pipeline
Decode
Execute
CDP: Coprocessor pipeline
Decode
Exception
entry start
Execute
Exception
continues
Memory
(Latecancelled)
CPCLK
CPID[31:0]
CPRT
nCPMREQ
CPPASS
CPLATECANCEL
CHSDE[1:0]
CHSEX[1:0]
LAST
Ignored
Dabort
(ARM920T
internal)
Figure 7-5 ARM920T late canceled CDP
7-14
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Coprocessor Interface
7.6
Privileged instructions
The coprocessor can restrict certain instructions for use in priv ileged modes only. To
do this, the coprocessor must track the nCPTRANS output. Figure 7-6 shows how
nCPTRANS changes after a mode change.
Mode change
Execute
Execute
(Cycle 2)
Execute
(Cycle 3)
Memory
Write
CDP: ARM processor pipeline
Decode
Decode
Decode
Execute
Memory
Decode
CDP: Coprocessor pipeline
Decode
Decode
Execute
Memory
Write
Write
CPCLK
CPID[31:0]
CPRT
nCPMREQ
nCPTRANS
*
Old mode
New mode
CPPASS
CPLATECANCEL
CHSDE[1:0]
CHSEX[1:0]
Ignored
Ignored
LAST
Ignored
Figure 7-6 ARM920T privileged instructions
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
7-15
Coprocessor Interface
In Figure 7-6 on page 7-15 the mode change (marked with an asterisk) occurs as
follows:
•
For mode changes that do not use an MSR. The mode changes after the first execute
cycle.
•
For mode changes that use an MSR. The mode changes after the second execute
cycle.
Note
The first two CHSDE[1:0] responses are ignored by the ARM920T because it is only
the final CHSDE[1:0] response, as the instruction moves from Decode into Execute,
that is relevant. This allows the coprocessor to change its response as nCPTRANS
changes.
7-16
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Coprocessor Interface
7.7
Busy-waiting and interrupts
The coprocessor is permitted to stall (or busy-wait) the processor during the execution
of a coprocessor instruction if, for example, it is still busy with an earlier coprocessor
instruction. To do so, the coprocessor associated with the Decode stage instruction must
drive WAIT in CHSDE[1:0]. When the instruction concerned enters the Execute stage
of the pipeline, the coprocessor can drive WAIT onto CHSEX[1:0] for as many cycles
as required to keep the instruction in the busy-wait loop.
For interrupt latency reasons the coprocessor can be interrupted while busy-waiting,
causing the instruction to be abandoned. Abandoning execution is achieved through
CPPASS. The coprocessor must monitor the state of CPPASS during every busy-wait
cycle. If it is HIGH, the instruction must still be executed. If it is LOW, the instruction
must be abandoned. Figure 7-7 on page 7-18 shows a busy-waited coprocessor
instruction being abandoned due to an interrupt.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
7-17
Coprocessor Interface
ARM processor pipeline
Coprocessor pipeline
Decode
Execute
(WAIT)
Decode
Execute
(WAIT)
Execute
(WAIT)
Execute
(WAIT)
Execute
(WAIT)
Execute
interrupted
Execute
(WAIT)
Exception
entry
Execute
(WAIT)
Abandoned
CPCLK
CPID[31:0]
CPInstr
nCPMREQ
CPPASS
CPLATECANCEL
CHSDE[1:0]
CHSEX[1:0]
WAIT
WAIT
WAIT
WAIT
Ignored
CPDOUT[31:0]
LDC/MCR
CPDIN[31:0]
STC/MRC
Figure 7-7 ARM920T busy waiting and interrupts
7-18
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Chapter 8
Trace Interface Port
This chapter gives a brief description of the Embedded Trace Macrocell (ETM) support
for the ARM920T processor. It contains the following section:
•
About the ETM interface on page 8-2.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
8-1
Trace Interface Port
8.1
About the ETM interface
The ARM920T trace interface port enables simple connection of an ETM9 to an
ARM920T Rev 1. This interface does not exist on ARM920T Rev 0. The ARM9
Embedded Trace Macrocell (ETM9) provides instruction and data trace for the
ARM9TDMI family of processors.
The interface is made up as follows:
•
ETMPWRDOWN input to the ARM920T
•
ETMCLOCK output to the ETM9
•
ETMnWAIT output to the ETM9
•
ETM<signal> outputs to the ETM9.
When ETMPWRDOWN is HIGH, the ETMCLOCK output and the ETM<signal>
outputs are held stable. When ETMPWRDOWN is LOW, the ETMCLOCK and
ETM<signal> outputs are enabled. This enables system power to be reduced when the
ETM9 is not used. When the ETM9 is incorporated within a system, the ARM debug
tools control ETMPWRDOWN, automatically setting the signal LOW at the start of a
debug session. If the ETM9 is not incorporated within a system, then
ETMPWRDOWN must be tied HIGH.
The ETMCLOCK output to the ETM9 is used by the ETM9 to sample the
ETM<signal> outputs on the rising edge of ETMCLOCK, when ETMnWAIT is
HIGH. ETMnWAIT is the nWAIT input signal to the ARM9TDMI, so this allows
cycle-accurate tracing using ETMCLOCK. The ETMCLOCK signal is never
stretched.
The ETM<signal> outputs are registered so that they can be sampled on the rising edge
of ETMCLOCK.
The ETM<signal> timing is shown in Timing definitions for the ARM920T Trace
Interface Port on page 13-26 and signal descriptions in ARM920T Trace Interface Port
signals on page A-13.
The ETM9 (Rev0/0a) Technical Reference Manual contains details of how to integrate
an ETM9 with an ARM920T Rev 1, including the pin correlation.
8-2
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Chapter 9
Debug Support
This chapter describes the debug support for the ARM920T, including the
EmbeddedICE macrocell. It contains the following sections:
•
About debug on page 9-2
•
Debug systems on page 9-3
•
Debug interface signals on page 9-5
•
Scan chains and JTAG interface on page 9-11
•
The JTAG state machine on page 9-12
•
Test data registers on page 9-19
•
ARM920T core clocks on page 9-42
•
Clock switching during debug on page 9-43
•
Clock switching during test on page 9-44
•
Determining the core state and system state on page 9-45
•
Exit from debug state on page 9-48
•
The behavior of the program counter during debug on page 9-51
•
EmbeddedICE macrocell on page 9-54
•
Vector catching on page 9-62
•
Single-stepping on page 9-63
•
Debug communications channel on page 9-64.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-1
Debug Support
9.1
About debug
Debug support is implemented using the ARM9TDMI CPU core embedded within the
ARM920T. Throughout this chapter therefore, ARM9TDMI refers to this core.
The ARM920T debug interface is based on IEEE Std. 1149.1- 1990, Standard Test
Access Port and Boundary-Scan Architecture. See this standard for an explanation of
the terms used in this chapter and for a description of the TAP controller states.
The ARM920T contains hardware extensions for advanced debugging features. These
are intended to ease the development of application software, operating systems, and the
hardware itself.
The debug extensions allow the core to be stopped by one of the following:
•
a given instruction fetch (breakpoint)
•
a data access (watchpoint)
•
asynchronously by a debug request.
When this happens, the ARM920T is said to be in debug state. At this point, you can
examine the internal state of the core and the external state of the system. When
examination is complete, you can restore the core and system state and resume program
execution.
The ARM920T is forced into debug state either by a request on one of the external
debug interface signals, or by an internal functional unit known as the EmbeddedICE
macrocell. When in debug state, the core isolates itself from the memory system. You
can then examine the core can while all other system activity continues as normal.
You can examine the internal state of the ARM920T using a JTAG-style serial interface.
This allows instructions to be serially inserted into the pipeline of the core without using
the external data bus. Therefore, when in debug state, you can insert a store-multiple
(STM) into the instruction pipeline to export the contents of the ARM9TDMI registers.
This data can be serially shifted out without affecting the rest of the system.
9-2
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
9.2
Debug systems
The ARM920T forms one component of a debug system that interfaces from the
high-level debugging performed by you, to the low-level interface supported by the
ARM920T. A typical system is shown in Figure 9-1.
Debug
host
Host computer running armsd or ADW
Protocol
converter
for example, Multi-ICE
Debug
target
Development system containing ARM920T
Figure 9-1 Typical debug system
This typical system has three parts:
•
The debug host on page 9-3
•
The protocol converter on page 9-4
•
The ARM920T processor on page 9-4.
9.2.1
The debug host
The debug host is a computer, for example a personal computer, running a software
debugger such as armsd, for example, or ADW. The debug host allows you to issue
high-level commands such as set breakpoint at location XX, or examine the contents of
memory from 0x0 to 0x100.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-3
Debug Support
9.2.2
The protocol converter
The debug host is connected to the ARM920T development system using an interface
(an RS232, for example). The messages broadcast over this connection must be
converted to the interface signals of the ARM920T. This function is performed by a
protocol converter, for example, Multi-ICE.
9.2.3
The ARM920T processor
The ARM920T processor, with hardware debug extensions, is the lowest level of the
system. The debug extensions allow you to:
•
stall the core from program execution
•
examine its internal state and the state of the memory system
•
resume program execution.
The debug host and the protocol converter are system-dependent.
9-4
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
9.3
Debug interface signals
There are four primary external signals associated with the debug interface:
•
IEBKPT, DEWPT, and EDBGRQ. The system can use these to ask the
ARM920T to enter debug state.
•
DBGACK. The ARM920T uses this signal to flag back to the system when it is
in debug state.
9.3.1
Entry into debug state on breakpoint
Any instruction being fetched from memory is latched at the end of phase 2. To apply a
breakpoint to that instruction, the breakpoint signal must be asserted by the end of the
following phase 1. This minimizes the setup time, giving the EmbeddedICE macrocell
an entire phase to perform the comparison. This is shown in Figure 9-2.
F1
D1
F2
E1
D2
FI
Ddebug
W1
M2
EI
M1
E2
DI
GCLK
w1
Edebug1
Edebug2
W2
MI
WI
w2
wI
IA[31:0]
ID[31:0]
1
2
I
3
4
IEBKPT
DBGACK
Figure 9-2 Breakpoint timing
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-5
Debug Support
You can build external logic, such as additional breakpoint comparators, to extend the
functionality of the EmbeddedICE macrocell. You must apply the external logic output
to the IEBKPT input. This signal is ORed with the internally generated breakpoint
signal before being applied to the ARM920T core control logic.
A breakpointed instruction is allowed to enter the Execute stage of the pipeline, but any
state change as a result of the instruction is prevented. All writes from previous
instructions complete as normal.
The Decode cycle of the debug entry sequence occurs during the Execute cycle of the
breakpointed instruction. The latched breakpoint signal forces the processor to start the
debug sequence.
9.3.2
Breakpoints and exceptions
A breakpointed instruction might have a Prefetch Abort associated with it. If so, the
Prefetch Abort takes priority and the breakpoint is ignored. (If there is a Prefetch Abort,
instruction data might be invalid, the breakpoint might have been data-dependent, and
as the data might be incorrect, the breakpoint might have been triggered incorrectly.)
SWI and undefined instructions are treated in the same way as any other instruction that
might have a breakpoint set on it. Therefore, the breakpoint takes priority over the SWI
or undefined instruction.
On an instruction boundary, if there is a breakpointed instruction and an interrupt (IRQ
or FIQ), the interrupt is taken and the breakpointed instruction is discarded. When the
interrupt has been serviced, the execution flow is returned to the original program.
This means that the instruction that has been breakpointed is fetched again, and if the
breakpoint is still set, the processor enters debug state when it reaches the Execute stage
of the pipeline.
When the processor has entered debug state, it is important that additional interrupts do
not affect the instructions executed. For this reason, as soon as the processor enters
debug state, interrupts are disabled, although the state of the I and F bits in the Program
Status Register (PSR) are not affected.
9.3.3
Watchpoints
Entry into debug state following a watchpointed memory access is imprecise. This is
necessary because of the nature of the pipeline and the timing of the watchpoint signal.
9-6
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
After a watchpointed access, the next instruction in the processor pipeline is always
allowed to complete execution. Where this instruction is a single-cycle data-processing
instruction, entry into debug state is delayed for one cycle while the instruction
completes. The timing of debug entry following a watchpointed load in this case is
shown in Figure 9-3 on page 9-8.
Note
Although instruction 5 enters the Execute state, it is not executed, and there is no state
update as a result of this instruction. When the debugging session is complete, normal
continuation involves a return to instruction 5, the next instruction in the code sequence
to be executed.
The instruction following the instruction that generated the watchpoint might have
modified the Program Counter (PC). If this happens, it is not possible to determine the
instruction that caused the watchpoint. A timing diagram showing debug entry after a
watchpoint where the next instruction is a branch is shown in Figure 9-4 on page 9-9.
However, you can always restart the processor.
When the processor has entered debug state, the ARM920T core can be interrogated to
determine its state. In the case of a watchpoint, the PC contains a value that is five
instructions on from the address of the next instruction to be executed. Therefore, if on
entry to debug state, in ARM state, the instruction SUB PC, PC, #20 is scanned in and the
processor restarted, execution flow returns to the next instruction in the code sequence.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-7
Debug Support
Ddebug
F1
FDp
F5
DDp
F2
FLDR
D2
DLDR
E2
ELDR
M2
D1
E1
M1
W1
w1
GCLK
D5
EDp
E5
MDp
MLDR
W2
WLDR
w2
M5
WDp
wLDR
Edebug1
Edebug2
W5
wDp
w5
w6
InMREQ
ID[31:0]
1
2
LDR
Dp
5
6
7
8
DA[31:0]
DD[31:0]
DDIN[31:0]
Watchpoint
DBGACK
Figure 9-3 Watchpoint entry with data processing instruction
9-8
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
Ddebug
FB
DLDR
FLDR
DB
ELDR
FT
MB
WLDR
EB
MLDR
DT
WB
Edebug1
Edebug2
ET
GCLK
InMREQ
IA[31:1]
A
ID[31:0]
LDR
A+4
B
T
A+8
X
X
T+4
T
T+8
T+1
T+C
T+2
T+3
DA[31:0]
DD[31:0]
DDIN[31:0]
Watchpoint
DBGACK
Figure 9-4 Watchpoint entry with branch
9.3.4
Watchpoints and exceptions
If there is an abort in the data access together with a watchpoint, the watchpoint
condition is latched, the exception entry sequence performed, and then the processor
enters debug state. If there is an interrupt pending, again the ARM920T processor
allows the exception entry sequence to occur and then enters debug state.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-9
Debug Support
9.3.5
Debug request
A debug request can take place through the EmbeddedICE macrocell or by asserting the
EDBGRQ signal. The request is synchronized and passed to the processor. Debug
request takes priority over any pending interrupt. Following synchronization, the core
enters debug state when the instruction at the Execute stage of the pipeline has
completely finished executing (when Memory and Write stages of the pipeline have
completed). While waiting for the instruction to finish executing, no more instructions
are issued to the Execute stage of the pipeline.
9.3.6
Actions of the ARM920T in debug state
When the ARM920T is in debug state, both memory interfaces indicate internal cycles.
This allows the rest of the memory system to ignore the ARM9TDMI core and function
as normal. Because the rest of the system continues operation, the ARM9TDMI core
ignores aborts and interrupts.
The BIGEND signal must not be changed by the system while in debug state. If it
changes there might be a synchronization problem, and the ARM920T (as seen by the
programmer) changes without the knowledge of the debugger. The BnRES signal must
also be held stable during debug. If the system applies reset to the ARM920T (BnRES
is driven LOW), the state of the ARM920T changes without the knowledge of the
debugger.
When instructions are executed in debug state, the ARM9TDMI core changes
asynchronously to the memory system outputs (except for InMREQ, ISEQ,
DnMREQ, and DSEQ that change synchronously from GCLK). For example, every
time a new instruction is scanned into the pipeline, the instruction address bus changes.
If the instruction is a load or store operation, the data address bus changes as the
instruction executes. Although this is asynchronous, it does not affect the system,
because both interfaces indicate internal cycles. You must take care when designing the
memory controller to ensure that this does not become a problem.
9-10
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
9.4
Scan chains and JTAG interface
There are six scan chains inside the ARM920T processor. These allow testing,
debugging, and programming of the EmbeddedICE macrocell watchpoint units. The
scan chains are controlled by a JTAG-style Test Access Port (TAP) controller. In
addition, support is provided for an optional seventh scan chain. This is intended to be
used for an external boundary scan chain around the pads of a packaged device. The
signals provided for this scan chain are described in Scan chain 3 on page 9-30.
The six scan chains of the ARM920T processor are called scan chain 0, 1, 2, 3, 4, and
15.
Note
The ARM920T TAP controller supports 32 scan chains. Scan chains 0 to 15 have been
reserved for use by ARM. Any extension scan chains must be implemented in the
remaining space. The SCREG[4:0] signals indicate the scan chain being accessed.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-11
Debug Support
9.5
The JTAG state machine
The process of serial test and debug is best explained in conjunction with the JTAG state
machine. Figure 9-5 shows the state transitions that occur in the TAP controller.
The state numbers are also shown on the diagram. These are output from the ARM920T
on the TAPSM[3:0] bits.
Test-Logic-Reset
0xF
tms=1
tms=0
Run-Test/Idle
0xC
tms=1
Select-DR-Scan
0x7
tms=0
Select-IR-Scan
0x4
tms=1
tms=0
tms=1
tms=0
tms=1
Capture-DR
0x6
Capture-IR
0xE
tms=0
tms=0
Shift-DR
0x2
tms=1
Shift-IR
0xA
tms=0
tms=1
tms=1
Exit1-DR
0x1
Pause-IR
0xB
tms=0
Exit2-DR
0x0
tms=1
tms=0
Update-DR
0x5
tms=0
tms=0
Exit2-IR
0x8
tms=1
tms=1
tms=1
tms=0
Pause-DR
0x3
tms=0
tms=0
Exit1-IR
0x9
tms=0
tms=1
tms=1
tms=1
Update-IR
0xD
tms=1
tms=0
Figure 9-5 Test access port (TAP) controller state transitions1
1. From IEEE Std 1149.1-1990. Copyright 1999IEEE. All rights reserved.
9-12
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
9.5.1
Reset
The JTAG interface includes a state-machine controller, the TAP controller. To force the
TAP controller into the correct state after power-up of the device, a reset pulse must be
applied to the nTRST signal, or the JTAG state machine must be cycled through the test
logic reset state. Before the JTAG interface can be used, nTRST must be driven LOW,
and then HIGH again. If you do not intend using the boundary scan interface, you can
tie the nTRST input permanently LOW.
Note
A clock on TCK is not required to reset the device.
The action of reset is as follows:
9.5.2
1.
System mode is selected. The boundary scan chain cells do not intercept any of
the signals passing between the external system and the core.
2.
The IDCODE instruction is selected. If the TAP controller is put into the
SHIFT-DR state and TCK is pulsed, the contents of the ID register are clocked
out of TDO.
Pullup resistors
The IEEE 1149.1 standard effectively requires TDI and TMS to have internal pullup
resistors. In order to minimize static current draw, these resistors are not fitted to the
ARM9TDMI core. Accordingly, the four inputs to the test interface (the TDO, TDI, and
TMS signals, plus TCK) must all be driven to valid logic levels to achieve normal
circuit operation.
9.5.3
Instruction register
The instruction register is four bits in length. There is no parity bit. The fixed value
loaded into the instruction register during the CAPTURE-IR controller state is 0001.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-13
Debug Support
9.5.4
Public instructions
Table 9-1 shows the public instructions that are supported.
Table 9-1 Public instructions
Instruction
Binary code
EXTEST
0000
SCAN_N
0010
INTEST
1100
IDCODE
1110
BYPASS
1111
CLAMP
0101
HIGHZ
0111
CLAMPZ
1001
SAMPLE/PRELOAD
0011
RESTART
0100
In the descriptions that follow, TDI and TMS are sampled on the rising edge of TCK
and all output transitions on TDO occur as a result of the falling edge of TCK.
EXTEST (0000)
The selected scan chain is placed in test mode by the EXTEST instruction. The
EXTEST instruction connects the selected scan chain between TDI and TDO.
When the instruction register is loaded with the EXTEST instruction, all the scan cells
are placed in their test mode of operation.
In the CAPTURE-DR state, inputs from the system logic and outputs from the output
scan cells to the system are captured by the scan cells.
In the SHIFT-DR state, the previously captured test data is shifted out of the scan chain
on TDO, while new test data is shifted in on the TDI input. This data is applied
immediately to the system logic and system pins.
9-14
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ARM DDI 0151C
Debug Support
SCAN_N (0010)
This instruction connects the scan path select register between TDI and TDO.
During the CAPTURE-DR state, the fixed value 10000 is loaded into the register.
During the SHIFT-DR state, the ID number of the desired scan path is shifted into the
scan path select register.
In the UPDATE-DR state, the scan register of the selected scan chain is connected
between TDI and TDO, and remains connected until a subsequent SCAN_N instruction
is issued. On reset, scan chain 3 is selected by default. The scan path select register is
five bits long in this implementation, although no finite length is specified.
INTEST (1100)
The selected scan chain is placed in test mode by the INTEST instruction. The INTEST
instruction connects the selected scan chain between TDI and TDO.
When the instruction register is loaded with the INTEST instruction, all the scan cells
are placed in their test mode of operation.
In the CAPTURE-DR state, the value of the data applied from the core logic to the
output scan cells, and the value of the data applied from the system logic to the input
scan cells is captured.
In the SHIFT-DR state, the previously captured test data is shifted out of the scan chain
on the TDO pin, while new test data is shifted in on the TDI pin.
IDCODE (1110)
The IDCODE instruction connects the device identification register (or ID register)
between TDI and TDO. The ID register is a 32-bit register that allows the manufacturer,
part number, and version of a component to be determined through the TAP. The ID
register is loaded from the TAPID[31:0] input bus. This must be tied to a constant value
that represents the unique JTAG IDCODE for the device.
When the instruction register is loaded with the IDCODE instruction, all the scan cells
are placed in their normal (system) mode of operation.
In the CAPTURE-DR state, the device identification code is captured by the ID register.
In the SHIFT-DR state, the previously captured device identification code is shifted out
of the ID register on the TDO pin, while data is shifted in on the TDI pin into the ID
register.
In the UPDATE-DR state, the ID register is unaffected.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-15
Debug Support
BYPASS (1111)
The BYPASS instruction connects a 1-bit shift register (the bypass register) between
TDI and TDO.
When the BYPASS instruction is loaded into the instruction register, all the scan cells
are placed in their normal (system) mode of operation. This instruction has no effect on
the system pins.
In the CAPTURE-DR state, a logic 0 is captured by the bypass register.
In the SHIFT-DR state, test data is shifted into the bypass register on TDI and out on
TDO after a delay of one TCK cycle. The first bit shifted out is a zero.
The bypass register is not affected in the UPDATE-DR state.
Note
All unused instruction codes default to the BYPASS instruction.
CLAMP (0101)
This instruction connects a 1-bit shift register (the bypass register) between TDI and
TDO.
When the CLAMP instruction is loaded into the instruction register, the state of all the
output signals is defined by the values previously loaded into the currently-loaded scan
chain.
Note
This instruction must only be used when scan chain 0 is the currently selected scan
chain.
In the CAPTURE-DR state, a logic 0 is captured by the bypass register.
In the SHIFT-DR state, test data is shifted into the bypass register on TDI and out on
TDO after a delay of one TCK cycle. The first bit shifted out is a zero.
The bypass register is not affected in the UPDATE-DR state.
HIGHZ (0111)
This instruction connects a 1-bit shift register (the bypass register) between TDI and
TDO.
9-16
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
When the HIGHZ instruction is loaded into the instruction register and scan chain 0 is
selected, all ARM920T outputs are driven to the high impedance state and the external
HIGHZ signal is driven HIGH. This is as if the signal TBE had been driven LOW.
In the CAPTURE-DR state, a logic 0 is captured by the bypass register. In the
SHIFT-DR state, test data is shifted into the bypass register on TDI and out on TDO
after a delay of one TCK cycle. The first bit shifted out is a zero.
The bypass register is not affected in the UPDATE-DR state.
CLAMPZ (1001)
This instruction connects a 1-bit shift register (the bypass register) between TDI and
TDO.
When the CLAMPZ instruction is loaded into the instruction register and scan chain 0
is selected, all the 3-state outputs (as described above) are placed in their inactive state,
but the data supplied to the outputs is derived from the scan cells. The purpose of this
instruction is to ensure that, during production test, each output can be disabled when
its data value is either a logic 0 or logic 1.
In the CAPTURE-DR state, a logic 0 is captured by the bypass register.
In the SHIFT-DR state, test data is shifted into the bypass register on TDI and out on
TDO after a delay of one TCK cycle. The first bit shifted out is a zero.
The bypass register is not affected in the UPDATE-DR state.
SAMPLE/PRELOAD (0011)
When the instruction register is loaded with the SAMPLE/PRELOAD instruction, all
the scan cells of the selected scan chain are placed in the normal mode of operation.
In the CAPTURE-DR state, a snapshot of the signals of the boundary scan is taken on
the rising edge of TCK. Normal system operation is unaffected.
In the SHIFT-DR state, the sampled test data is shifted out of the boundary scan on the
TDO pin, while new data is shifted in on the TDI pin to preload the boundary scan
parallel input latch. This data is not applied to the system logic or system pins while the
SAMPLE/PRELOAD instruction is active.
This instruction must be used to preload the boundary scan register with known data
prior to selecting INTEST or EXTEST instructions.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-17
Debug Support
RESTART (0100)
This instruction is used to restart the processor on exit from debug state. The RESTART
instruction connects the bypass register between TDI and TDO and the TAP controller
behaves as if the BYPASS instruction is loaded. The processor resynchronizes back to
the memory system when the RUN-TEST/IDLE state is entered.
9-18
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
9.6
Test data registers
You can connect the following test data registers between TDI and TDO:
•
Bypass register on page 9-19
•
ARM920T device identification (ID) code register on page 9-19
•
Instruction register on page 9-20
•
Scan chain select register on page 9-20
•
Scan chains 0, 1, 2, and 3 on page 9-23
•
Scan chain 6 on page 9-31
•
Scan chains 4 and 15, the ARM920T memory system on page 9-31.
9.6.1
9.6.2
Bypass register
Purpose
Bypasses the device during scan testing by providing a path
between TDI and TDO.
Length
1 bit.
Operating mode
When the BYPASS instruction is the current instruction in the
instruction register, serial data is transferred from TDI to TDO in
the SHIFT-DR state with a delay of one TCK cycle. There is no
parallel output from the bypass register. A logic 0 is loaded from
the parallel input of the bypass register in CAPTURE-DR state.
ARM920T device identification (ID) code register
ARM DDI 0151C
Purpose
Reads the 32-bit device identification code. No programmable
supplementary identification code is provided.
Length
32 bits.
Operating mode
When the IDCODE instruction is current, the ID register is
selected as the serial path between TDI and TDO. There is no
parallel output from the ID register. The 32-bit identification code
is loaded into the register from the parallel inputs of the
TAPID[31:0] input bus during the CAPTURE-DR state.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-19
Debug Support
The IEEE format of the ID register is shown in Table 9-2.
Table 9-2 ID code register
Bits
Function
Value
31:28
Specification revision
0x1
27:12
Product code
0x0920
11:1
Manufacturer
Default = 0b11110000111
0
IEEE standard specified
0b1
The TAPID[31:0] pins allow you to set this value when the macrocell is instantiated in
a design.
9.6.3
Instruction register
Purpose
Changes the current TAP instruction.
Length
4 bits.
Operating mode
When in SHIFT-IR state, the instruction register is selected as the
serial path between TDI and TDO.
During the CAPTURE-IR state, the value b0001 is loaded into this register. This is
shifted out during SHIFT-IR (least significant bit first), while a new instruction is
shifted in (least significant bit first). During the UPDATE-IR state, the value in the
instruction register becomes the current instruction. On reset, IDCODE becomes the
current instruction.
9.6.4
Scan chain select register
Purpose
Changes the current active scan chain.
Length
5 bits.
Operating mode
After SCAN_N has been selected as the current instruction, when
in SHIFT-DR state, the scan chain select register is selected as the
serial path between TDI and TDO.
During the CAPTURE-DR state, the value b10000 is loaded into this register. This is
shifted out during SHIFT-DR, least significant bit first, while a new value is shifted in,
least significant bit first.
9-20
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
During the UPDATE-DR state, the value in the register selects a scan chain to become
the currently active scan chain. All additional instructions such as INTEST then apply
to that scan chain.
The currently selected scan chain only changes when a SCAN_N instruction is
executed, or a reset occurs. On reset, scan chain 3 is selected as the active scan chain.
The number of the currently selected scan chain is reflected on the SCREG[4:0] output
bus. You can use the TAP controller to drive external scan chains in addition to those
within the ARM920T macrocell. The external scan chain must be assigned a number
and control signals for it, and can be derived from SCREG[4:0], IR[3:0],
TAPSM[3:0], TCK1, and TCK2.
The list of scan chain numbers allocated by ARM are shown in Table 9-3 on page 9-23.
An external scan chain can take any other number. The serial data stream applied to the
external scan chain is made present on SDIN. The serial data back from the scan chain
must be presented to the TAP controller on the SDOUTBS input.
The scan chain present between SDIN and SDOUTBS is connected between TDI and
TDO whenever scan chain 3 is selected, or when any of the unassigned scan chain
numbers is selected. If there is more than one external scan chain, you must build a
multiplexor externally to apply the desired scan chain output to SDOUTBS. You can
control the multiplexor by decoding SCREG[4:0]. The structure is shown in Figure 9-6
on page 9-22.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-21
Debug Support
SDIN
SDOUTBS
Scan chain 3
3
!3
ARMTDO
TAP
controller
SCREG
!6
6
ETM9
TDO
SDIN
SDOUTBS
SCREG
TAP
controller
TDI
TMS
TCK
SCREG
0
1
2
4
15
3, 5-14,
16-31
ARM920T
TDO
TDO
Figure 9-6 External scan chain multiplexor
9-22
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
Scan chain number allocations are shown in Table 9-3.
Table 9-3 Scan chain number allocation
Scan
chain
number
9.6.5
Function
0
ARM9TDMI macrocell scan
test
1
Debug
2
EmbeddedICE programming
3
External boundary scan
4
Physical address TAG RAM
5
Reserved
6
ETM9
7:14
Reserved
15
Coprocessor 15
16:31
Unassigned
Scan chains 0, 1, 2, and 3
These scan chains allow serial access to the core logic, and to the EmbeddedICE
macrocell for programming purposes. Each scan cell can perform two basic functions:
•
capture
•
shift.
Scan chain 0
ARM DDI 0151C
Purpose
Primarily for inter-device testing (EXTEST), and testing the
ARM9TDMI core (INTEST). Scan chain 0 is selected using the
SCAN_N instruction.
Length
184 bits.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-23
Debug Support
INTEST allows serial testing of the core. The TAP controller must be placed in the
INTEST mode after scan chain 0 has been selected:
•
During CAPTURE-DR, the current outputs from the core logic are captured in the
output cells.
•
During SHIFT-DR, this captured data is shifted out while a new serial test pattern
is scanned in, applying known stimuli to the inputs.
•
During RUN-TEST/IDLE, the core is clocked. Normally, the TAP controller only
spends one cycle in RUN-TEST/IDLE. The whole operation can then be repeated.
EXTEST allows inter-device testing, useful for verifying the connections between
devices in the design. The TAP controller must be placed in EXTEST mode after scan
chain 0 has been selected:
•
During CAPTURE-DR, the current inputs to the core logic from the system are
captured in the input cells.
•
During SHIFT-DR, this captured data is shifted out while a new serial test pattern
is scanned in, applying known values on the core outputs.
•
During RUN-TEST/IDLE, the core is not clocked.
The operation can then be repeated.
The bit order of scan chain 0 is shown in Table 9-4.
Table 9-4 Scan chain 0 bit order
9-24
No.
Signal
Direction
1
ID[0]
Input
2
ID[1]
Input
3:31
ID[2:30]
Input
32
ID[31]
Input
33
SYSSPEED
Internal
34
WPTANDBKPT
Internal
35
DDEN
Output
36
DD[31]
Bidirectional
37
DD[30]
Bidirectional
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
Table 9-4 Scan chain 0 bit order (continued)
ARM DDI 0151C
No.
Signal
Direction
38:66
DD[29:1]
Bidirectional
67
DD[0]
Bidirectional
68
DA[31]
Output
69
DA[30]
Output
70:98
DA[29:1]
Output
99
DA[0]
Output
100
IA[31]
Output
101
IA[30]
Output
102:129
IA[29:2]
Output
130
IA[1]
Output
131
IEBKPT
Input
132
DEWPT
Input
133
EDBGRQ
Input
134
EXTERN0
Input
135
EXTERN1
Input
136
COMMRX
Output
137
COMMTX
Output
138
DBGACK
Output
139
RANGEOUT0
Output
140
RANGEOUT1
Output
141
DBGRQI
Output
142
DDBE
Input
143
InMREQ
Output
144
DnMREQ
Output
145
DnRW
Output
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-25
Debug Support
Table 9-4 Scan chain 0 bit order (continued)
9-26
No.
Signal
Direction
146
DMAS[1]
Output
147
DMAS[0]
Output
148
PASS
Output
149
LATECANCEL
Output
150
ITBIT
Output
151
InTRANS
Output
152
DnTRANS
Output
153
nRESET
Input
154
nWAIT
Input
155
IABORT
Input
156
IABE
Input
157
DABORT
Input
158
DABE
Input
159
nFIQ
Input
160
nIRQ
Input
161
ISYNC
Input
162
BIGEND
Input
163
HIVECS
Input
164
CHSD[1]
Input
165
CHSD[0]
Input
166
CHSE[1]
Input
167
CHSE[0]
Input
168
Reserved
-
169
ISEQ
Output
170
InM[4]
Output
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
Table 9-4 Scan chain 0 bit order (continued)
ARM DDI 0151C
No.
Signal
Direction
171
InM[3]
Output
172
InM[2]
Output
173
InM[1]
Output
174
InM[0]
Output
175
DnM[4]
Output
176
DnM[3]
Output
177
DnM[2]
Output
178
DnM[1]
Output
179
DnM[0]
Output
180
DSEQ
Output
181
DMORE
Output
182
DLOCK
Output
183
ECLK
Output
184
INSTREXEC
Output
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-27
Debug Support
Scan chain 1
Purpose
Primarily for debugging. Scan chain 1 is selected using the
SCAN_N TAP controller instruction.
Length
67 bits.
The bit functions of scan chain 1 are shown in Table 9-5.
Table 9-5 Scan chain 1 bit function
Bit
Function
67:36
Data values DD[0:31]
35:33
Control bits DDEN,
WPTANDBKPT, and
SYSSPEED
32:1
Instruction data ID[31:0]
This scan chain is 67 bits long, 32 bits for data values, 32 bits for instruction data, and
three control bits, SYSSPEED, WPTANDBKPT, and DDEN. The three control bits
serve four different purposes:
9-28
•
Under normal INTEST test conditions, the DDEN signal can be captured and
examined.
•
During EXTEST conditions, a known value can be scanned into DDEN to be
driven into the rest of the system. If a logic 1 is scanned into DDEN, the data data
bus DD[31:0] drives out the values stored in its scan cells. If a logic 0 is scanned
into DDEN, DD[31:0] captures the current input values.
•
While debugging, the value placed in the SYSSPEED control bit determines
whether the ARM920T synchronizes back to system speed before executing the
instruction.
•
After the ARM920T has entered debug state, the first time SYSSPEED is
captured and scanned out, its value tells the debugger whether the core has entered
debug state due to a breakpoint (SYSSPEED LOW), or a watchpoint
(SYSSPEED HIGH). You can have a watchpoint and breakpoint condition occur
simultaneously. When a watchpoint condition occurs, the WPTANDBKPT bit
must be examined by the debugger to determine whether the instruction currently
in the execute stage of the pipeline is breakpointed. If so, WPTANDBKPT is
HIGH, otherwise it is LOW.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
Scan chain 2
Purpose
Allows access to the EmbeddedICE hardware registers. The order
of the scan chain from TDI to TDO is:
•
read/write
•
register address bits 4 to 0
•
data values bits 31 to 0.
Length
38 bits.
Table 9-6 shows the bit functions of scan chain 2.
Table 9-6 Scan chain 2 bit function
Bit
Function
37
Read = 0
Write = 1
36:32
EmbeddedICE address register
31:0
Data values
To access this serial register, scan chain 2 must first be selected using the SCAN_N TAP
controller instruction. The TAP controller must then be placed in INTEST mode:
ARM DDI 0151C
•
No action is taken during CAPTURE-DR.
•
During SHIFT-DR, a data value is shifted into the serial register. Bits 32 to 36
specify the address of the EmbeddedICE hardware register to be accessed.
•
During UPDATE-DR, this register is either read or written depending on the value
of bit 37 (0 = read).
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-29
Debug Support
Scan chain 3
Purpose
Allows the ARM920T to control an external boundary scan chain.
Length
User-defined.
Scan chain 3 is provided so that you can control an optional external boundary scan
chain using the ARM920T. Typically this is used for a scan chain around the pad ring
of a packaged device. The following control signals are provided, and are generated
only when scan chain 3 is selected. These outputs are inactive at all other times:
DRIVEOUTBS
This switches the scan cells from system mode to test mode. This
signal is asserted whenever the INTEST, EXTEST, CLAMP, or
CLAMPZ instruction is selected.
PCLKBS
This is the update clock, generated in the UPDATE-DR state.
Typically the value scanned into the chain is transferred to the cell
output on the rising edge of this signal.
ICAPCLKBS, ECAPCLKBS
These are the capture clocks used to sample data into the scan cells
during INTEST and EXTEST respectively. These clocks are
generated in the CAPTURE-DR state.
SHCLK1BS, SHCLK2BS
These are non-overlapping clocks generated in the SHIFT-DR
state that are used to clock the master and slave element of the
scan cells respectively. When the state machine is not in the
SHIFT-DR state, both these clocks are LOW.
nHIGHZ
You can use this signal to drive the outputs of the scan cells to the
high impedance state. This signal is driven LOW when the
HIGHZ instruction is loaded into the instruction register, and
HIGH at all other times.
In addition to these control outputs, SDIN output and SDOUTBS input are also
provided. When an external scan chain is in use, SDOUTBS must be connected to the
serial data output and SDIN must be connected to the serial data input.
9-30
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
9.6.6
Scan chain 6
Purpose
You use scan chain 6 to program the registers in the ETM9.
Length
The chain length is 40 bits, comprising:
•
a 32-bit data field
•
a 7-bit address field
•
a read/write bit.
To write an ETM9 register:
•
the data to be written is placed in the data field
•
the register address is in the address field
•
the read/write bit is set to 1.
To read an ETM9 register:
•
the data field is ignored
•
the register address is in the address field
•
the read/write bit is set to 0.
The ETM9 registers are read or written when the TAP controller enters the
UPDATE-DR state.
For more details of the ETM9 registers, see the ETM9 (Rev1) Technical Reference
Manual.
9.6.7
Scan chains 4 and 15, the ARM920T memory system
On entry to debug state, the debugger must extract and save the state of CP15. It is
advisable that the caches and MMUs are then switched off to prevent any debug
accesses to memory altering their state. At this point, the debugger can non-invasively
determine the state of the memory system. When in debug state, the debugger can see
the state of the ARM920T memory system. This includes:
•
CP15
•
caches
•
MMU
•
PA TAG RAM.
Scan chains 4 and 15 are reserved for this use.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-31
Debug Support
Scan chain 15
This scan chain is 40 bits long. The format of the scan chain is dependent on the access
mode used. The formats for both modes for scan chain 15 are shown in Table 9-7.
Table 9-7 Scan chain 15 format and access modes
Interpreted access mode
Physical access mode
Function
Read/write
Function
Read/write
39
0
Write
nR/W
Write
38:33
000000
Write
Register address
Write
32:1
Instruction word
Write
Register value
Read/write
0
0
Write
1
Write
Scan chain bit
With scan chain 15 selected, TDI is connected to bit 39 and TDO is connected to bit 0.
An access using this scan chain allows all of the CP15 registers to be read and written,
the cache CAM and RAM to be read, and the TLB CAM and RAM to be read. There
are two access modes available using scan chain 15. These are:
•
Physical access mode
•
Interpreted access mode on page 9-34.
Physical access mode
You can do a physical access mode operation using scan chain 15 as follows:
9-32
1.
In SHIFT-DR, shift in the read/write bit, register address and register value for
writing, shown in Table 9-8 on page 9-33.
2.
Move through UPDATE-DR. For a write, the register is updated here.
3.
For reading, return to SHIFT-DR through CAPTURE-DR and shift out the
register value.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
Table 9-8 shows the bit format for scan chain 15 physical access mode operations.
Table 9-8 Scan chain 15 physical access mode bit format
Scan chain bit
Function
Read/
write
39
nR/W
Write
38:33
Register address
Write
32:1
Register value
Read/
write
0
1
Write
The mapping of the 6-bit register address field to the CP15 registers for physical access
mode is shown in Table 9-9.
Table 9-9 Physical access mapping to CP15 registers
Address
ARM DDI 0151C
Register
[38]
[37:34]
[33]
Number
Name
Type
0
0x0
0
C0
ID register
Read
0
0x0
1
C0
Cache type
Read
0
0x1
0
C1
Control
Read/write
0
0x9
0
C9
Data cache lockdown
Read
0
0x9
1
C9
Instruction cache lockdown
Read
0
0xD
0
C13
Process ID
Read/write
0
0xF
0
C15.State
Test state
Read/write
1
0xD
1
C15.C.I.Ind
Instruction cache index
Read
1
0xE
1
C15.C.D.Ind
Data cache index
Read
1
0x1
1
C15.C.I
Instruction cache
Read/write
1
0x2
1
C15.C.D
Data cache
Read/write
1
0x5
0
C15.M.I
Instruction MMU
Read
1
0x6
0
C15.M.D
Data MMU
Read
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-33
Debug Support
Interpreted access mode
You can do an interpreted access mode operation using scan chain 15 as follows:
1.
A physical access read-modify-write to C15 (test state) must be done in order to
set bit 0, CP15 interpret.
2.
The required MCR/MRC instruction word is shifted in to scan chain 15.
3.
A system-speed LDR (read) or STR (write) is performed on the ARM9TDMI.
4.
CP15 responds to this LDR/STR by executing the coprocessor instruction in its scan
chain.
5.
In the case of a LDR, the data is returned to the ARM9TDMI and can be captured
onto scan chain 1 by performing an STR.
6.
In the case of an STR, the interpreted MCR completes with the data that is issued
from the ARM9TDMI.
7.
A physical access read-modify-write to C15 (test state) must be done in order to
clear CP15 interpret, bit 0.
Table 9-10 shows the bit format for scan chain 15 interpreted access mode operations.
Table 9-10 Scan chain 15 interpreted access mode bit format
Scan chain bit
Function
Read/
write
39
0
Write
38:33
000000
Write
32:1
Instruction word
Write
0
0
Write
The mapping of the 32-bit instruction word field to the remaining CP15 registers
supported for interpreted access mode is shown in Table 9-11 on page 9-35, Table 9-12
on page 9-36, and Table 9-13 on page 9-36. This supported subset is used for cache and
MMU debug operations. Using interpreted accesses for other CP15 register operations
produces UNPREDICTABLE behavior. The construction of a CP15 instruction word
from ARM assembler is shown in Figure 2-1 on page 2-7.
For the MCR, Rd has been replaced by r0, because the register being used as the source
data is governed by the STR. For the MRC, Rd has been replaced by r0, because the register
being used as the destination is governed by the LDR.
9-34
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
The mapping of the 32-bit instruction word field to the remaining CP15 registers for
interpreted access mode is shown in Table 9-11. The construction of a CP15 instruction
word from ARM assembler is shown in CP15 register map summary on page 2-5.
Table 9-11 Interpreted access mapping to CP15 registers
ARM920T
instruction
Function
Rd
Ra
CP15 instruction
STR Rd,[Ra]
Write I TTB
TTB
-
MCR p15,5,r0,c15,c1,2
LDR Rd,[Ra]
Read I TTB
TTB
-
MRC p15,5,r0,c15,c1,2
STR Rd,[Ra]
Write D TTB
TTB
-
MCR p15,5,r0,c15,c2,2
LDR Rd,[Ra]
Read D TTB
TTB
-
MRC p15,0,r0,c2,c2,2
STR Rd,[Ra]
Write I DAC
DAC
-
MCR p15,5,r0,c15,c1,3
LDR Rd,[Ra]
Read I DAC
DAC
-
MRC p15,5,r0,c15,c1,3
STR Rd,[Ra]
Write D DAC
DAC
-
MCR p15,5,r0,c15,c2,3
LDR Rd,[Ra]
Read D DAC
DAC
-
MRC p15,0,r0,c3,c0,0
STR Rd,[Ra]
Write I FSR
FSR
-
MCR p15,0,r0,c5,c0,1
LDR Rd,[Ra]
Read I FSR
FSR
-
MRC p15,0,r0,c5,c0,1
STR Rd,[Ra]
Write D FSR
FSR
-
MCR p15,0,r0,c5,c0,0
LDR Rd,[Ra]
Read D FSR
FSR
-
MRC p15,0,r0,c5,c0,0
STR Rd,[Ra]
Write I FAR
FAR
-
MCR p15,0,r0,c6,c0,1
LDR Rd,[Ra]
Read I FAR
FAR
-
MRC p15,0,r0,c6,c0,1
STR Rd,[Ra]
Write D FAR
FAR
-
MCR p15,0,r0,c6,c0,0
LDR Rd,[Ra]
Read D FAR
FAR
-
MRC p15,0,r0,c6,c0,0
STR Rd,[Ra]
ICache invalidate all
-
-
MCR p15,0,r0,c7,c5,0
STR Rd,[Ra]
ICache invalidate entry
-
Tag, Seg
MCR p15,0,r0,c7,c5,1
STR Rd,[Ra]
DCache invalidate all
-
-
MCR p15,0,r0,c7,c6,0
STR Rd,[Ra]
DCache invalidate entry
-
Tag ,Seg
MCR p15,0,r0,c7,c6,1
STR Rd,[Ra]
Write ICache victim
-
Victim, Seg
MCR p15,0,r0,c9,c1,1
STR Rd,[Ra]
Write DCache victim
-
Victim, Seg
MCR p15,0,r0,c9,c1,0
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-35
Debug Support
Table 9-11 Interpreted access mapping to CP15 registers (continued)
ARM920T
instruction
Function
Rd
Ra
CP15 instruction
STR Rd,[Ra]
Write ICache victim and lockdown
base
-
Victim
MCR p15,0,r0,c9,c0,1
STR Rd,[Ra]
Write DCache victim and lockdown
base
-
Victim
MCR p15,0,r0,c9,c0,0
STR Rd,[Ra]
Write I TLB lockdown
Base,Victim
-
MCR p15,0,r0,c10,c0,1
LDR Rd,[Ra]
Read I TLB lockdown
Base,Victim
-
MRC p15,0,r0,c10,c0,1
STR Rd,[Ra]
Write D TLB lockdown
Base,Victim
-
MCR p15,0,r0,c10,c0,0
LDR Rd,[Ra]
Read D TLB lockdown
Base,Victim
-
MRC p15,0,r0,c10,c0,0
Table 9-12 Interpreted access mapping to the MMU
ARM920T instruction
Function
Rd/Rlist
Ra
CP15 instruction
LDR Rd,[Ra] or LDMIA Ra,[Rlist]
I CAM Read
MVA Tag, Size, V, P
-
MCR p15,4,r0,c15,c5,4
LDR Rd,[Ra] or LDMIA Ra,[Rlist]
I RAM1 Read
Protection
-
MCR p15,4,r0,c15,c9,4
LDR Rd,[Ra]or LDMIA Ra,[Rlist]
I RAM2 Read
PA Tag, Size
-
MCR p15,4,r0,c15,c1,5
LDR Rd,[Ra]or LDMIA Ra,[Rlist]
D CAM Read
MVA Tag, Size, V, P
-
MCR p15,4,r0,c15,c6,4
LDR Rd,[Ra]or LDMIA Ra,[Rlist]
D RAM1 Read
Protection
-
MCR p15,4,r0,c15,c10,4
LDR Rd,[Ra]or LDMIA Ra,[Rlist]
D RAM2 Read
PA Tag, Size
-
MCR p15,4,r0,c15,c2,5
Table 9-13 Interpreted access mapping to the caches
ARM920T instruction
Function
Rd/Rlist
Ra
CP15 instruction
LDR Rd,[Ra] or LDMIA
Ra,[Rlist]
I CAM Read
Tag, Seg, Dirty
Seg
MCR p15,2,r0,c15,c5,2
LDR Rd,[Ra] or LDMIA
Ra,[Rlist]
I RAM Read
Data
Seg, Word
MCR p15,2,r0,c15,c9,2
LDR Rd,[Ra]or LDMIA
Ra,[Rlist]
D CAM Read
Tag, Seg ,Dirty
Seg
MCR p15,2,r0,c15,c6,2
LDR Rd,[Ra] or LDMIA
Ra,[Rlist]
D RAM Read
Data
Seg, Word
MCR p15,2,r0,c15,c10,2
9-36
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
Debug access to the MMU
This is achieved through scan chain 1 and 15, using the physical access and interpreted
access modes. The following steps explain how to read the Data TLB
ARM DDI 0151C
1.
Physical access: Read-modify-write cp15, register 1, to turn off both the caches
and MMU.
2.
Physical access: Read-modify-write cp15, register 15, to set MMU test and CP15
interpret mode.
3.
Interpreted access: LDR Rd,[Ra]. MCR = Read D TLB lockdown. This will read
the Base and Victim to Rd.
4.
Physical access: Read-modify-write CP15 register 15 to clear CP 15 interpret
mode.
5.
STR of Rd loaded in step (3). Capture on scan chain 1 and shift out.
6.
Physical access: Read-modify-write CP15 register 15 to set CP15 interpret mode.
7.
Interpreted access: STR Rd,[Ra]. MCR = Write D TLB lockdown, where Rd =
Base[read in (3)], Victim[=0].
8.
Interpreted access: 8 word LDM, LDMIA Ra,[Rlist]. MCR = D CAM Read. The
CAM Read will increment the victim pointer on every access, so this will read
entries 0-7.
9.
Physical access: Read-modify-write CP15 register 15 to clear CP 15 interpret
mode.
10.
8 word STM of the values loaded in step (6). Capture these on scan chain 1 and
shift out. These 8 values are the CAM Tag for entries 0-7.
11.
Physical access: Read-modify-write CP15 register 15 to set CP15 interpret mode.
12.
Repeat steps (8) to (11) eight times to read entries 0-63.
13.
Interpreted access: STR Rd,[Ra]. MCR = Write D TLB lockdown, where Rd =
Base[read in step (3)], Victim[=0].
14.
Interpreted access: LDR Rd,[Ra]. MCR = D RAM1 Read. The RAM1 Read will
increment the victim pointer on every access as MMU test in cp15, register 15,
Test State register has been set.
15.
Interpreted access: LDR Rd,[Ra]. MCR = D RAM2 Read. This uses a pipelined
version of the last RAM1 read.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-37
Debug Support
16.
Physical access: Read-modify-write CP15 register 15 to clear CP 15 interpret
mode.
17.
2 word STM of the values loaded in steps (10) and (11). Capture these on scan
chain 1 and shift out. These 2 values are RAM1 and RAM2 from entry 0.
18.
Physical access: Read-modify-write CP15 register 15 to set CP15 interpret mode.
19.
Repeat steps (14) to (18) 64 times to read RAM1 and RAM2 entries 0-63.
20.
Interpreted access: STR Rd,[Ra]. MCR = Write D TLB lockdown, where Rd =
Base[read in step (3)], Victim[read in step (3)].
21.
Physical access: Read-modify-write cp15, register 15, to clear MMU test and
CP15 interpret mode.
22.
Physical access: Read-modify-write cp15, register 1, to turn on (restore state of)
both the caches and MMU.
Debug access to the caches
This is achieved through scan chain 1 and 15, using the physical access and interpreted
access modes. The following steps explain how to read the DCache. They assume you
are trying to read the contents of segment 2 of the DCache.
9-38
1.
Physical access: Read-modify-write cp15, register 1, to turn off both the caches
and MMU.
2.
Physical access: Read-modify-write cp15, register 15, to set CP15 interpret mode.
3.
Interpreted access: LDR Rd,[Ra]. MCR = D CAM Read, where Ra = Seg2. This
will cause the current victim for segment 2 to be read into C15.C.D.Ind.
4.
Physical access: Read C15.C.D.Ind which contains the victim of segment 2.
5.
Interpreted access: STR Rd,[Ra]. MCR = Write DCache victim, where Ra =
Victim0, Seg2. This sets the victim counter to 0 for segment 2, and configures the
counter to increment after a CAM read or write. The Base remains unchanged.
6.
Interpreted access: 8 word LDM, LDMIA Ra,[Rlist]. MCR = D RAM Read,
where Ra = seg2, word0. The LDMIA will increment the word part of the address
and move across the cache line from word0 to word7.
7.
Interpreted access: LDR Rd,[Ra]. MCR = D CAM Read, where Ra = Seg2.
8.
Physical access: Read-modify-write cp15, register 15, to clear CP15 interpret
mode.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
9.
9 word STM of the values loaded in (6) and (7). Capture these on scan chain 1 and
shift out. These 9 values are the CAM Tag and RAM cache line data for segment
2, index 0.
10.
Physical access: Read-modify-write cp15, register 15, to set CP15 interpret mode.
11.
Increment the victim (+1) and repeat steps (5) to (10) 64 times. This approach
avoids using the auto increment capability of the victim counter. If the auto
increment capability is used, the victim counter will loop back to the Base value
when it reaches 63, so either the Victim must start at 0, or the Base must be read,
set to 0, then restored after reading the memory.By starting the victim at 0, repeat
steps (6) to (10) 64 times.
12.
Interpreted access: STR Rd,[Ra]. MCR = Write DCache victim, where Ra =
Victim, Seg2. The Victim value should be the value read and saved in step (5).
13.
Repeat steps (3) to (12) for each segment.
14.
Physical access: Read-modify-write cp15, register 15, to clear CP15 interpret
mode.
15.
Physical access: Read-modify-write cp15, register 1, to turn on (restore state of)
both the caches and MMU.
Scan chain 4 - debug access to the PA TAG RAM
This scan chain is 49 bits long, as shown in Table 9-14.
Table 9-14 Scan chain 4 format
ARM DDI 0151C
Scan
chain
bit
Function
Read/
write
48
PA TAG sel TCK
Write
47
RAM enable
Write
46
Odd not even
Write
45:40
Scan index [5:0]
Write
39:33
Scan seg [6:0]
Write
32
PA TAG sync TCK
Read
31:0
WBPA
Read
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-39
Debug Support
With scan chain 4 selected, TDI is connected to bit 48 and TDO is connected to bit 0.
An access using this scan chain allows the physical address TAG RAM to be read.
Figure 9-7 shows the construction of write back physical addresses.
31
6 5 4 3
0
0 0 0 0
PA TAG
Scan Odd
seg[0] not
even
Figure 9-7 Write back physical address format
Note
Although Scan Seg [6:0] is provided, only bits [2:0] are used in ARM920T to address
segments 0-7. Bits [6:3] are defined for forwards compatibility.
To read an entry in the PA TAG RAM, you must execute the following sequence:
1.
Write:
•
PA TAG sel TCK = 1
•
RAM enable = 0.
This synchronizes the PA TAG RAM to TCK, the test clock.
2.
Read PA TAG sync TCK until it is 1.
This confirms that the PA TAG RAM is synchronized to TCK.
3.
9-40
Write:
•
PA TAG sel TCK = 1
•
RAM enable = 1
•
odd not even
•
scan index bits [5:0]
•
scan seg bits [2:0].
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
4.
Go through the UPDATE-DR state of the ARM920T TAP controller three times.
The most efficient way of doing this, after doing the write in step 3 is to go
through the following sequence. This avoids rewriting the values in step 3 on each
iteration:
a.
EXIT1-DR
b.
UPDATE-DR
c.
SELECT-DR-SCAN
d.
CAPTURE-DR
e.
Repeat (a) to (d) x 2
f.
SHIFT-DR.
The PA TAG RAM requires three clock cycles to perform the read. Its clock is
cycled in UPDATE-DR, and therefore this state must be passed through three
times.
5.
Read the Write Back Physical Address (WBPA).
6.
Write:
•
PA TAG sel TCK = 0
•
RAM enable = 0.
Resynchronize the PA TAG RAM to the system clock.
7.
Read PA TAG sync TCK until it is 0. This confirms that resynchronization has
occurred.
You must repeat this sequence of steps (1 to 7) for the eight segments, corresponding to
the eight DCache segments, and the 64 entries per segment, corresponding to the 64
entries in each DCache segment.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-41
Debug Support
9.7
ARM920T core clocks
The ARM9TDMI core has two clocks:
•
the memory clock GCLK
•
an internally TCK generated clock, DCLK.
During normal operation, the core is clocked by GCLK, and internal logic holds DCLK
LOW. When the ARM920T is in the debug state, the core is clocked by DCLK under
control of the TAP state machine, and GCLK can free run. The selected clock is output
on the ECLK signal for use by the external system.
Note
When the core is being debugged and is running from DCLK, nWAIT has no effect.
The two cases where the clocks switch are:
•
during debugging
•
during testing.
9-42
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
9.8
Clock switching during debug
When the ARM9TDMI core enters debug state, it must switch from GCLK to DCLK.
This is handled automatically by logic in the ARM9TDMI core. On entry to debug state,
the ARM9TDMI asserts DBGACK in the HIGH phase of GCLK. The switch between
the two clocks occurs on the next falling edge of GCLK as shown in Figure 9-8.
GCLK
DBGACK
DCLK
ECLK
Figure 9-8 Clock switching on entry to debug state
The ARM9TDMI core is forced to use DCLK as the primary clock until debugging is
complete. On exit from debug, the core must be allowed to synchronize back to GCLK.
You must do this in the following sequence:
ARM DDI 0151C
1.
Shift the final instruction of the debug sequence into the instruction data bus scan
chain, and clock it in by asserting DCLK. At this point, clock RESTART into the
TAP controller register.
2.
The ARM9TDMI core now automatically resynchronizes back to GCLK when
the TAP controller enters the RUN-TEST/IDLE mode and starts fetching
instructions from memory at GCLK speed. For more information, see Exit from
debug state on page 9-48.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-43
Debug Support
9.9
Clock switching during test
Under serial test conditions, when test patterns are being applied to the core through the
JTAG interface, the ARM9TDMI CPU core must be clocked using DCLK. Entry into
test is less automatic than debug and some care must be taken.
On the way into test, GCLK must be held LOW. You can now use the TAP controller
to perform serial testing on the ARM9TDMI core. If scan chain 0 and INTEST are
selected, DCLK is generated while the state machine is in RUN-TEST/IDLE state.
During EXTEST, DCLK is not generated.
On exit from test, you must select RESTART as the TAP controller instruction. When
this is done, you can allow GCLK to resume. After INTEST testing, you must take care
to ensure that the core is in a sensible state before switching back. The safest way to do
this is either:
•
select RESTART and then cause a system reset
•
insert MOV PC,#0 into the instruction pipeline before switching back.
9-44
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
9.10
Determining the core state and system state
When the ARM9TDMI core is in debug state, you can examine the core state and
system state. You can do this by forcing load and store multiples into the pipeline.
Before you can examine the core state and system state, the debugger must first
determine whether the processor entered debug from Thumb state or ARM state. You
can do this by examining bit 4 of the EmbeddedICE macrocell debug status register. If
this is HIGH, the core is in Thumb state. If it is LOW, the core is in ARM state.
9.10.1
Determining the core state
If the processor has entered debug state from Thumb state, it is easiest for the debugger
to force the core back into ARM state. When this is done, the debugger can execute the
same sequence of instructions to determine the processor state.
To force the processor into ARM state, the following sequence of Thumb instructions
can be executed on the core:
STR
MOV
STR
BX
MOV
MOV
R0,
R0,
R0,
PC
R8,
R8,
[R1]
PC
[R1]
R8
R8
;
;
;
;
;
;
Save R0 before use
Copy PC into R0
Save the PC in R0
Jump into ARM state
NOP (no operation)
NOP
The above use of R1 as the base register for stores is for illustration only. You can use
any register.
Because all Thumb instructions are only 16 bits long, you can duplicate the instruction
in the instruction data bus bits, when shifting them into scan chain 1. For example, the
encoding for BX R0 is 0x4700. Therefore, if 0x47004700 is shifted into the 32 bits of the
instruction data bus of scan chain 1, the debugger does not have to remember the half
of the bus that the processor expects to read instructions from.
From this point, you can determine the processor state by the following series of steps
of ARM instructions.
When the processor is in ARM state, typically the first instruction executed is:
STM R0, {R0-R15}
This causes the contents of the registers to be made visible on the data data bus. These
values can then be sampled and shifted out.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-45
Debug Support
After determining the values in the current bank of registers, you might want to access
the banked registers. This can only be done by changing mode. Normally, a mode
change can only occur if the core is already in a privileged mode. However, while in
debug state, a mode change can occur from any mode into any other mode.
Note
The debugger must restore the original mode before exiting debug state.
For example, assume that the debugger has been asked to return the state of the User
mode and FIQ mode registers, and debug state has been entered in Supervisor mode.
The instruction sequence might be:
STMIA
MRS
STR
BIC
ORR
MSR
STMIA
ORR
MSR
STMIA
R0, {R0-R15}
R0, CPSR
R0, [R0]
R0, R0, #0x1F
R0, R0, #0x10
CPSR, R0
R0, {R13-R14}
R0, R0, #0x01
CPSR, R0
R0, {R8-R14}
; Save current registers
;
;
;
;
;
;
;
;
Save CPSR to determine current mode
Clear mode bits
Select USER mode
Enter USER mode
Save registers not previously visible
Select FIQ mode
Enter FIQ mode
Save banked FIQ registers
All these instructions are said to execute at debug speed. Debug speed is much slower
than system speed because, between each core clock, 67 scan clocks occur in order to
shift in an instruction or shift out data. Executing instructions more slowly than usual is
fine for accessing the core state because the ARM920T is fully static. However, you
cannot use this same method for determining the state of the rest of the system.
While in debug state, only the following instructions can be inserted into the instruction
pipeline for execution:
•
all data processing operations
•
all load, store, load multiple, and store multiple instructions
MSR and MRS.
•
9-46
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
9.10.2
Determining system state
To meet the dynamic timing requirements of the memory system, any attempt to access
system state must occur synchronously. Therefore, you must force the ARM9TDMI
core to synchronize back to system speed. The 33rd bit of scan chain 1, SYSSPEED,
controls this.
You can place a legal debug instruction in the instruction data bus of scan chain 1 with
bit 33 (the SYSSPEED bit) LOW. This instruction is then executed at debug speed. To
execute an instruction at system speed, a NOP (such as MOV R0, R0) must be scanned in
as the next instruction with bit 33 set HIGH.
After the system speed instructions have been scanned into the instruction data bus and
clocked into the pipeline, you must load the RESTART instruction into the TAP
controller. This causes the ARM9TDMI automatically to resynchronize back to GCLK
when the TAP controller enters RUN-TEST/IDLE state, and execute the instruction at
system speed. Debug state is re-entered after the instruction completes execution, when
the processor switches itself back to the internally generated DCLK. When the
instruction has completed, DBGACK is HIGH. At this point INTEST can be selected
in the TAP controller, and debugging can resume.
To determine whether a system speed instruction has completed, the debugger must
look at SYSCOMP (bit 3 of the debug status register). To access memory, the
ARM9TDMI must access memory through the data data bus interface, as this access can
be stalled indefinitely by nWAIT. Therefore, the only way to determine whether the
memory access has completed is to examine the SYSCOMP bit. When this bit is HIGH
the instruction has completed.
The state of the system memory can be passed to the debug host by using system speed
load multiples and debug store multiples.
9.10.3
Instructions that can have the SYSSPEED bit set
The only valid instructions to set this bit for are:
•
loads
•
stores
•
load multiple
•
store multiple.
When the ARM9TDMI returns to debug state after a system speed access, the
SYSSPEED bit is set HIGH.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-47
Debug Support
9.11
Exit from debug state
Leaving debug state involves restoring the internal state of the ARM9TDMI core,
causing a branch to the next instruction to be executed, and synchronizing back to
GCLK. After restoring the internal state, you must load a branch instruction into the
pipeline. For details on calculating the branch, see The behavior of the program counter
during debug on page 9-51.
Use bit 33 of scan chain 1 to force the ARM9TDMI core to resynchronize back to
GCLK. The penultimate instruction in the debug sequence is a branch to the instruction
where execution is to resume. This is scanned in with bit 33 set LOW. The core is then
clocked to load the branch into the pipeline. The final instruction that you must scan in
is a NOP (such as MOV R0, R0), with bit 33 set HIGH. You must the clock the core to
load this instruction into the pipeline. Now, select the RESTART instruction in the TAP
controller. When the state machine enters the RUN-TEST/IDLE state, the scan chain
reverts back to system mode and clock resynchronization to GCLK occurs within the
ARM9TDMI. Normal operation resumes, with instructions being fetched from
memory.
The delay, until the state machine is in RUN-TEST/IDLE state, allows you to set up
conditions in other devices in a multiprocessor system without taking immediate effect.
Then, when RUN-TEST/IDLE state is entered, all the processors resume operation
simultaneously.
The function of DBGACK is to tell the rest of the system when the ARM9TDMI core
is in debug state. You can use this to inhibit peripherals such as watchdog timers that
have real-time characteristics. Also, you can use DBGACK to mask out memory
accesses that are caused by the debugging process. For example, when the ARM9TDMI
core enters debug state after a breakpoint, the instruction pipeline contains the
breakpointed instruction plus two other instructions that have been prefetched. On entry
to debug state, the pipeline is flushed. So, on exit from debug state, the pipeline must be
refilled to its previous state. Therefore, because of the debugging process, more memory
accesses occur than are normally expected. You can inhibit any system peripheral that
might be sensitive to the number of memory accesses by using DBGACK.
Note
DBGACK can only be used in this way using breakpoints. It does not mask the correct
number of memory accesses after a watchpoint.
For example, consider a peripheral that merely counts the number of instruction fetches.
This device must return the same answer after a program has run both with and without
debugging. Figure 9-9 on page 9-49 shows the behavior of the ARM9TDMI core on
exit from debug state.
9-48
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
ECLK
InMREQ
ISEQ
IA[31:1]
Internal cycles
N
S
S
IAb
IAb+4
IAb+8
ID[31:0]
DBGACK
Figure 9-9 Debug exit sequence
Figure 9-10 on page 9-50 shows that two instructions are fetched after the instruction
that breakpoints. Figure 9-10 on page 9-50 shows that DBGACK masks the first three
instruction fetches out of the debug state, corresponding to the breakpoint instruction,
and the two instructions prefetched after it.
Note
When a system speed access occurs, DBGACK remains HIGH, masking any memory
access.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-49
Debug Support
GCLK
InMREQ
ISEQ
Memory cycles
Internal cycles
IA[31:1]
ID[31:0]
1
3
2
IEBKPT
DBGACK
Figure 9-10 Debug state entry
9-50
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
9.12
The behavior of the program counter during debug
To force the ARM9TDMI core to branch back to the place where program flow is
interrupted by debug, the debugger must keep track of what happens to the PC. There
are six cases:
•
Breakpoint on page 9-51
•
Watchpoint on page 9-51
•
Watchpoint with another exception on page 9-52
•
Watchpoint and breakpoint on page 9-52
•
Debug request on page 9-52
•
System speed accesses on page 9-53.
In each case the same equation is used to determine where to resume execution.
9.12.1
Breakpoint
Entry to debug state from a breakpointed instruction advances the PC by 16 bytes in
ARM state, or 8 bytes in Thumb state. Each instruction executed in debug state
advances the PC by one address. The normal way to exit from debug state after a
breakpoint is to remove the breakpoint, and branch back to the previously breakpointed
address.
For example, if the ARM9TDMI core entered debug state from a breakpoint set on a
given address and two debug speed instructions were executed, a branch of 7 addresses
must occur (four for debug entry, plus two for the instructions, plus one for the final
branch). The following sequence shows ARM instructions scanned into scan chain 1.
This is Most Significant Bit (MSB) first, so the first digit represents the value to be
scanned into the SYSSPEED bit, followed by the instruction.
0 EAFFFFF9
1 E1A00000
; B -7 addresses (two’s complement)
; NOP (MOV R0, R0), SYSSPEED bit is set
For small branches, the final branch can be replaced with a subtract, with the PC as the
destination. For example, SUB PC, PC, #28 for ARM code.
9.12.2
Watchpoint
You can return to program execution after entering debug state from a watchpoint in the
same way as the procedure described in Breakpoint above. Debug entry adds four
addresses to the PC, and every instruction adds one address. Because the instruction
after the one that caused the watchpoint has executed, execution resumes at the
following instruction.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-51
Debug Support
9.12.3
Watchpoint with another exception
If a watchpoint access simultaneously causes a Data Abort, the ARM9TDMI core enters
debug state in abort mode. Entry into debug is held off until the core has changed into
abort mode, and fetched the instruction from the abort vector.
A similar sequence is followed when an interrupt, or any other exception, occurs during
a watchpointed memory access. The ARM9TDMI core enters debug state in the mode
of the exception, and so the debugger must check to see whether this happened. The
debugger can deduce whether an exception occurred by looking at the current and
previous mode, (in the CPSR and SPSR), and the value of the PC. If an exception did
take place, you must have the choice to service the exception before debugging or not.
For example, suppose an abort occurred on a watchpoint access, and ten instructions
had been executed to determine this. You can use the following sequence to return to
program execution:
0 EAFFFFF1
1 E1A00000
; B -15 addresses (two’s complement)
; NOP (MOV R0, R0), SYSSPEED bit is set
This forces a branch back to the abort vector, causing the instructions at that location to
be refetched and executed. After the abort service routine, the instruction that caused
the abort and watchpoint is re-executed. This causes the watchpoint to be generated and
the ARM9TDMI enters debug state again.
9.12.4
Watchpoint and breakpoint
It is possible to have a watchpoint and breakpoint condition occurring simultaneously.
This can happen when an instruction causes a watchpoint, and the following instruction
has been breakpointed. The same calculation must be performed as for Breakpoint on
page 9-51 to determine where to resume. In this case, it is at the breakpoint instruction,
because this has not been executed.
9.12.5
Debug request
Entry into debug state as a result of a debug request is similar to a breakpoint and, as for
breakpoint entry to debug state, adds four addresses to the PC, and every instruction
executed in debug state adds one.
For example, the following sequence handles a situation where a debug request has been
invoked, followed by a decision to return to program execution immediately:
0 EAFFFFFB
1 E1A00000
; B -5 addresses (two’s complement)
; NOP (MOV R0, R0), SYSSPEED bit is set
This restores the PC, and restarts the program from the next instruction.
9-52
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
9.12.6
System speed accesses
If a system speed access is performed during debug state, the value of the PC is
increased by five addresses. Because system speed instructions access the memory
system, it is possible for aborts to take place. If an abort occurs during a system speed
memory access, the ARM9TDMI core enters abort mode before returning to debug
state.
This is similar to an aborted watchpoint. However, the problem is much harder to fix
because the abort is not caused by an instruction in the main program, and the PC does
not point to the instruction that caused the abort. An abort handler usually looks at the
PC to determine the instruction that caused the abort, and therefore the abort address.
In this case, the value of the PC is invalid, but the debugger knows the address of the
location being accessed. Therefore the debugger can be written to help the abort handler
fix the memory system.
9.12.7
Summary of return address calculations
The calculation of the branch return address can be summarized as:
-(4 + N +5S)
Where N is the number of debug speed instructions executed (including the final
branch), and S is the number of system speed instructions executed.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-53
Debug Support
9.13
EmbeddedICE macrocell
The EmbeddedICE macrocell is integral to the ARM9TDMI processor core. It has two
hardware breakpoint or watchpoint units. You can configure each of them to monitor
the instruction memory interface or the data memory interface. Each watchpoint unit
has a value and mask register, with an address field, a data field, and a control field.
Because the ARM9TDMI processor core has a Harvard architecture, you must specify
whether the watchpoint registers examine the instruction or the data interface. This is
specified by bit 3:
•
when bit 3 is set, the data interface is examined
•
when bit 3 is clear, the instruction interface is examined.
There can be no don’t care case for this bit because the comparators cannot compare the
values on both buses simultaneously. Therefore, bit 3 of the control mask register is
always clear and cannot be programmed HIGH. Bit 3 also determines whether the
internal breakpoint or watchpoint signal must be driven by the result of the comparison.
Figure 9-11 on page 9-56 gives an overview of the operation of the EmbeddedICE
macrocell.
The ARM9TDMI EmbeddedICE macrocell has logic that allows single stepping
through code. This reduces the work required by an external debugger, and removes the
requirement to flush the instruction cache. There is also hardware to allow efficient
trapping of accesses to the exception vectors. These blocks of logic free the two
general-purpose hardware breakpoint or watchpoint units for use by the programmer at
all times.
9.13.1
Register map
The EmbeddedICE macrocell register map is shown in Table 9-15.
Table 9-15 ARM9TDMI EmbeddedICE macrocell register map
9-54
Address
Width
Function
00000
4
Debug control
00001
5
Debug status
00010
8
Vector catch control
00100
6
Debug comms control
00101
32
Debug comms data
01000
32
Watchpoint 0 address value
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
Table 9-15 ARM9TDMI EmbeddedICE macrocell register map (continued)
Address
Width
Function
01001
32
Watchpoint 0 address mask
01010
32
Watchpoint 0 data value
01011
32
Watchpoint 0 data mask
01100
9
Watchpoint 0 control value
01101
8
Watchpoint 0 control mask
10000
32
Watchpoint 1 address value
10001
32
Watchpoint 1 address mask
10010
32
Watchpoint 1 data value
10011
32
Watchpoint 1 data mask
10100
9
Watchpoint 1 control value
10101
8
Watchpoint 1 control mask
The general arrangement of the EmbeddedICE macrocell is shown in Figure 9-11 on
page 9-56.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-55
Debug Support
Scan chain
register
R/W
4
Address
Update
5
Address
decoder
0
Enable
31
Data
ID[31:0]
Address
Address
IA[31:0]
Value
Mask
D Control
Control
Control
Data
Breakpoint
Rangeout
DD[31:0]
Address
DA[31:0]
Data
32
Control
Data
I Control
0
Comparator
Registers
TDI
TDO
Figure 9-11 ARM9TDMI EmbeddedICE macrocell overview
As an example, if a watchpoint is requested on a particular memory location but the data
value is irrelevant, you can program the data mask register to 0xFFFF_FFFF, all bits set to
1. This ensures that the entire data bus value is ignored.
9.13.2
Using the mask registers
For each value register there is an associated mask register in the same format. Setting
a bit to 1 in the mask register causes the corresponding bit in the value register to be
ignored in any comparison.
9.13.3
Control registers
The format of the control registers depends on how bit 3 is programmed. If bit 3 is
programmed to be 1, the breakpoint comparators examine the data address, and data and
control signals. In this case, the format of the register is as shown in Figure 9-12 on
page 9-57.
9-56
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
8
7
6
ENABLE
RANGE
CHAIN
5
4
EXTERN DnTRANS
3
2
1
0
1
DMAS[1]
DMAS[0]
DnRW
Figure 9-12 Watchpoint control register for data comparison
Note
Bit 8 and bit 3 cannot be masked.
The functions of the watchpoint control register for data comparison bits are shown in
Table 9-16.
Table 9-16 Watchpoint control register, data comparison bit functions
ARM DDI 0151C
Bit
Name
Function
8
ENABLE
If a watchpoint match occurs, the internal watchpoint signal is only
asserted when the ENABLE bit is set. This bit only exists in the value
register. It cannot be masked.
7
RANGE
You can connect this bit to the range output of another watchpoint
register. In the ARM9TDMI EmbeddedICE macrocell, the address
comparator output of watchpoint 1 is connected to the RANGE input
of watchpoint 0. This allows you to couple two watchpoints for
detecting conditions that occur simultaneously, for example, for
range-checking.
6
CHAIN
You can connect this bit to chain output of another watchpoint to
implement, for example, debugger requests of the form breakpoint on
address YYY only when in process XXX.
In the ARM9TDMI EmbeddedICE macrocell, the CHAINOUT output
of watchpoint 1 is connected to the CHAIN input of watchpoint 0. The
CHAINOUT output is derived from a latch. The address and control
field comparator drives the write enable for the latch and the input to
the latch is the value of the data field comparator. The CHAINOUT
latch is cleared when the control value register is written or when
nTRST is LOW.
5
EXTERN
This is an external input into the EmbeddedICE macrocell that allows
the watchpoint to be dependent on some external condition. The
EXTERN input for watchpoint 0 is labeled EXTERN0, and the
EXTERN input for watchpoint 1 is labeled EXTERN1.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-57
Debug Support
Table 9-16 Watchpoint control register, data comparison bit functions (continued)
Bit
Name
Function
4
DnTRANS
This bit is compared with the data not translate signal from the core in
order to determine between a User mode (DnTRANS = 0) data transfer,
and a privileged mode (DnTRANS = 1) transfer.
2:1
DMAS[1:0]
These bits are compared with the DMAS[1:0] signal from the core in
order to detect the size of the data data bus activity.
0
DnRW
This bit is compared with the data not read/write signal from the core
in order to detect the direction of the data data bus activity. nRW is 0
for a read, and 1 for a write.
If bit 3 of the control register is programmed to 0, the comparators examine the
instruction address, instruction data, and instruction control buses. In this case bits [1:0]
of the mask register must be set to don’t care (programmed to 11). The format of the
register in this case is as shown in Figure 9-13.
8
7
6
5
4
3
2
1
0
ENABLE
RANGE
CHAIN
EXTERN
InTRANS
0
X
ITBIT
X
Figure 9-13 Watchpoint control register for instruction comparison
9-58
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
The functions of the watchpoint control register for instruction comparison bits are
shown in Table 9-17.
Table 9-17 Watchpoint control register for instruction comparison bit functions
ARM DDI 0151C
Bit
Name
Function
8
ENABLE
If a watchpoint match occurs, the internal breakpoint signal is only
asserted when the ENABLE bit is set. This bit only exists in the value
register, it cannot be masked.
7
RANGE
You can connect this bit to the range output of another watchpoint
register. In the ARM9TDMI EmbeddedICE macrocell, the address
comparator output of watchpoint 1 is connected to the RANGE input of
watchpoint 0. This allows you to couple two watchpoints for detecting
conditions that occur simultaneously, for example, for range-checking.
6
CHAIN
You can connect this bit to chain output of another watchpoint to
implement, for example, debugger requests of the form breakpoint on
address YYY only when in process XXX.
In the ARM9TDMI EmbeddedICE macrocell, the CHAINOUT output
of watchpoint 1 is connected to the CHAIN input of watchpoint 0. The
CHAINOUT output is derived from a latch. The address or control field
comparator drives the write enable for the latch, and the input to the latch
is the value of the data field comparator. The CHAINOUT latch is
cleared when the control value register is written, or when nTRST is
LOW.
5
EXTERN
This is an external input into the ARM9TDMI EmbeddedICE macrocell
that allows the watchpoint to be dependent on some external condition.
The EXTERN input for watchpoint 0 is labeled EXTERN0, and the
EXTERN input for watchpoint 1 is labeled EXTERN1.
4
InTRANS
This bit is compared with the not translate signal from the core in order
to determine between a User mode (InTRANS = 0) instruction fetch, and
a privileged mode (InTRANS = 1) instruction fetch.
1
ITBIT
This bit is compared with the Thumb state signal from the core to
determine between a Thumb (ITBIT = 1) instruction fetch or an ARM
(ITBIT = 0) instruction fetch.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-59
Debug Support
9.13.4
Debug control register
The ARM9TDMI debug control register is four bits wide and is shown in Figure 9-14.
3
2
1
0
Single step
INTDIS
DBGRQ
DBGACK
Figure 9-14 Debug control register
Bit 3 controls the single-step hardware. This is explained in more detail in Figure 9-17
on page 9-64.
9.13.5
Debug status register
The debug status register is five bits wide. If this register is accessed for a write (with
the read/write bit set HIGH), the status bits are written. If it is accessed for a read (with
the read/write bit LOW), the status bits are read.
4
8
ITBIT
7
6
SYSCOMP
1
2
3
5
4
IFEN
3
2
DBGRQ
0
1
0
DBGACK
Figure 9-15 Debug status register
The function of the bits in the debug status register are shown in Table 9-18.
Table 9-18 Debug status register bit functions
9-60
Bits
Function
4
Allows ITBIT to be read. This enables the debugger to determine what state the
processor is in, and therefore determine the instructions to execute.
3
Allows the state of the SYSCOMP bit from the core (synchronized to TCK) to be
read. This allows the debugger to determine that a memory access from the debug
state has completed.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
Table 9-18 Debug status register bit functions (continued)
9.13.6
Bits
Function
2
Allows the state of the core interrupt enable signal, IFEN, to be read. Because the
capture clock for the scan chain might be asynchronous to the processor clock, the
DBGACK output from the core is synchronized before being used to generate the
IFEN status bit.
1:0
Allow the values on the synchronized versions of DBGRQ and DBGACK to be read.
Vector catch register
The ARM9TDMI EmbeddedICE macrocell controls logic to enable accesses to the
exception vectors to be trapped in an efficient manner. This is controlled by the vector
catch register, as shown in Figure 9-16. The functionality is described in Vector
catching on page 9-62.
7
6
5
4
3
2
1
0
FIQ
IRQ
Reserved
D_Abort
P_Abort
SWI
Undefined
Reset
Figure 9-16 Vector catch register
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-61
Debug Support
9.14
Vector catching
The ARM9TDMI EmbeddedICE macrocell contains logic that allows efficient trapping
of fetches from the vectors during exceptions. This is controlled by the vector catch
register. If one of the bits in this register is set HIGH and the corresponding exception
occurs, the processor enters debug state as if a breakpoint has been set on an instruction
fetch from the relevant exception vector.
For example, if the processor executes a SWI instruction while bit 2 of the vector catch
register is set, the ARM9TDMI core fetches an instruction from location 0x8. The vector
catch hardware detects this access and forces the ARM9TDMI CPU core to enter debug
state.
The behavior of the hardware is independent of the watchpoint comparators, leaving
them free for general use. The vector catch register is sensitive only to fetches from the
vectors during exception entry. Therefore, if code branches to an address within the
vectors during normal operation, and the corresponding bit in the vector catch register
is set, the processor is not forced to enter debug state.
9-62
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
9.15
Single-stepping
The ARM9TDMI EmbeddedICE macrocell contains logic that allows efficient
single-stepping through code. This leaves the macrocell watchpoint comparators free
for general use.
This function is enabled by setting bit 3 of the debug control register. You must only
alter the state of this bit while the processor is in debug state. If the processor exits debug
state and this bit is HIGH, the processor fetches an instruction, executes it, and then
immediately re-enters debug state. This happens independently of the watchpoint
comparators. If a system-speed data access is performed while in debug state, the
debugger must ensure that the control bit is clear first.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-63
Debug Support
9.16
Debug communications channel
The ARM9TDMI EmbeddedICE macrocell contains a communication channel for
passing information between the target and the host debugger. This is implemented as
coprocessor 14.
The communications channel consists of:
•
a 32-bit wide comms data read register
•
a 32-bit wide comms data write register
•
a 6-bit wide comms control register for synchronized handshaking between the
processor and the asynchronous debugger.
These registers are in fixed locations in the EmbeddedICE register map, as shown in
Figure 9-11 on page 9-56. You can access the registers from the processor using MCR and
MRC instructions to coprocessor 14.
9.16.1
Debug comms channel register
The debug comms control register is read-only, and allows synchronized handshaking
between the processor and the debugger. The format of the debug comms control
register is shown in Figure 9-17.
31 30 29 28 27
2 1 0
0 0 1 0
W R
Figure 9-17 Debug comms control register
9-64
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
The function of each register bit is described in Table 9-19.
Table 9-19 Debug comms control register bit functions
Bits
Function
31:28
Contain a fixed pattern that denotes the EmbeddedICE macrocell version number, in
this case 0b0010.
27:2
Unused.
1
Denotes, as seen by the processor, whether the comms data write register is free. If,
as seen by the processor, the comms data write register is free (W=0), new data can
be written. If it is not free (W=1), the processor must poll until W=0. If, as seen by
the debugger, W=1, some new data has been written that can then be scanned out.
0
Denotes whether there is some new data in the comms data read register. If, as seen
by the processor, R=1, there is some new data that can be read using an MRC
instruction. If, as seen by the debugger, R=0, the comms data read register is free and
new data can be placed there through the scan chain. If R=1, this denotes that data
previously placed there through the scan chain has not been collected by the
processor, and so the debugger must wait.
From the perspective of the debugger, the registers are accessed using the scan chain in
the usual way. From the processor, these registers are accessed using coprocessor
register transfer instructions. You can use the following instructions:
MRC p14, 0, Rd, C0, C0
; Returns the debug comms control register into Rd.
MCR p14, 0, Rn, C1, C0
; Writes the value in Rn to the comms data write register.
MRC p14, 0, Rd, C1, C0
; Returns the debug data read register into Rd.
Note
The Thumb instruction set does not support coprocessors so the ARM9TDMI must be
operated in ARM state to access the debug comms channel.
ARM DDI 0151C
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9-65
Debug Support
9.16.2
Communications using the comms channel
There are two methods of communicating using the comms channel:
•
transmitting
•
receiving.
Sending a message to the debugger and Receiving a message from the debugger detail
their usage.
Sending a message to the debugger
When the processor wishes to send a message to the debugger, it must check that the
comms data write register is free for use by finding out if the W bit of the debug comms
control register is clear:
•
If the W bit is set, previously written data has not been read by the debugger. The
processor must continue to poll the control register until the W bit is clear.
•
If W bit is clear, the comms data write register is clear.
When the W bit is clear, a message can be written by a register transfer to coprocessor
14. As the data transfer occurs from the processor to the comms data write register, the
W bit is set in the debug comms control register.
The debugger sees a synchronized version of both the R and W bit when it polls the
debug comms control register through the JTAG interface. When the debugger sees the
W bit is set, it can read the comms data write register and scan the data out. The action
of reading this data register clears the debug comms control register W bit. At this point,
the communications process can begin again.
As an alternative to polling, the debug comms channel can be interrupt driven by
connecting the ARM920T COMMRX and COMMTX signals to the systems interrupt
controller.
Receiving a message from the debugger
Message transfer from the debugger to the processor is similar to sending a message to
the debugger. In this case, the debugger polls the R bit of the debug comms control
register:
9-66
•
if the R bit is LOW, the comms data read register is free, and data can be placed
there for the processor to read
•
if the R bit is set, previously deposited data has not yet been collected, so the
debugger must wait.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Debug Support
When the comms data read register is free, data can be written using the JTAG interface.
The action of this write sets the R bit in the debug comms control register.
When the processor polls this register, it sees a GCLK synchronized version. If the R
bit is set, there is data waiting to be collected. You can read this data read using an MRC
instruction to coprocessor 14. The action of this load clears the R bit in the debug
comms control register. When the debugger polls this register and sees that the R bit is
clear, the data has been taken, and the process can now be repeated.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
9-67
Debug Support
9-68
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Chapter 10
TrackingICE
This chapter describes how the ARM920T processor uses TrackingICE mode. It
contains the following sections:
•
About TrackingICE on page 10-2
•
Timing requirements on page 10-3
•
TrackingICE outputs on page 10-4.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
10-1
TrackingICE
10.1
About TrackingICE
When in TrackingICE mode, several ARM920T outputs track the inputs to the
ARM9TDMI processor core embedded within the ARM920T processor. You can then
connect an ARM9TDMI test chip to the outputs. This precisely tracks the ARM9TDMI
processor core inside the ARM920T, enabling all outputs of the ARM9TDMI core to
be observed.
Figure 10-1 shows how a tracking ARM9TDMI processor is attached to an ARM920T
processor.
ARM920T
ARM9TDMI
0
1
ARM9TDMI
1
TRACK
Figure 10-1 Using TrackingICE
The tracking ARM9TDMI processor operates one clock phase behind the actual
ARM9TDMI core (on the inverted clock). All required inputs to the ARM9TDMI core
are latched inside the ARM920T processor and are then brought out on various outputs.
You can attach the tracking ARM9TDMI processor to these outputs.
10-2
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
TrackingICE
10.2
Timing requirements
To enable the ARM9TDMI processor core to be tracked correctly, all inputs must be
synchronous to the ARM9TDMI processor clock. These inputs include TCK, that in
tracking mode is latched on the falling edge of GCLK before it is driven onto the
ARM920T tracking outputs. All other TCK relative signals, TDI, TMS, and
SDOUTBS, are latched on rising GCLK before they are driven onto the ARM920T
tracking outputs.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
10-3
TrackingICE
10.3
TrackingICE outputs
Table 10-1 shows the ARM920T outputs that are re-used when the ARM920T
processor is in TrackingICE mode.
Table 10-1 ARM920T in TrackingICE mode
10-4
ARM920T
output
Attach to
tracking
ARM9TDMI
input
IR[3:2]
CHSE[1:0]
IR[1:0]
CHSD[1:0]
SCREG[4]
nIRQ
SCREG[3]
nFIQ
SCREG[2]
DABORT
SCREG[1]
IABORT
TAPSM[3]
EXTERN1
TAPSM[2]
EXTERN0
TAPSM[1]
DEWPT
TAPSM[0]
IEBKPT
ICAPCLKBS
HIVECS
ECAPCLKBS
EDBGGQ
PCLKBS
nWAIT
RSTCLKBS
nRESET
SHCLK1BS
TDI
SHCLK2BS
TMS
TCK1
GCLK
TCK2
TCK
SDIN
SDOUTBS
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
TrackingICE
The remaining input connections to the ARM9TDMI core are:
•
ID bus attaches to the CPID bus
•
DD bus attaches to the CPDOUT bus
•
BIGEND input attaches to the BIGENDOUT.
These can still be attached to a coprocessor when the ARM920T processor is in tracking
mode. The only difference in behavior is that CPDOUT mirrors the ARM920T DD bus
on every cycle, not only for coprocessor data transfers. The following conditions apply:
ARM DDI 0151C
•
The ISYNC and nTRST inputs must be common between the ARM920T and the
tracking ARM9TDMI processor.
•
IABE and DABE of the tracking ARM9TDMI processor must be HIGH so that
the address outputs can be observed.
•
DDBE of the tracking ARM9TDMI processor must be LOW to prevent a drive
clash on the bidirectional DD bus. It is not necessary for the tracking
ARM9TDMI to drive the DD bus because CPDOUT is driven with the data from
all memory access cycles.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
10-5
TrackingICE
10-6
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Chapter 11
AMBA Test Interface
This chapter examines the ARM920T AMBA test interface. It contains the following
sections:
•
About the AMBA test interface on page 11-2
•
Entering and exiting AMBA Test on page 11-3
•
Functional test on page 11-4
•
Burst operations on page 11-11
•
PA TAG RAM test on page 11-12
•
Cache test on page 11-15
•
MMU test on page 11-19.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
11-1
AMBA Test Interface
11.1
About the AMBA test interface
You can use the ARM920T processor as an AMBA Revision D compliant ASB slave
for AMBA testing. The address space of the ARM920T Slave State Machine (SSM) is
from <base> to <base + 0xFFF>, word-aligned. The base address is specific to the
implementation of the AMBA decoder. In this chapter <base> is assumed to be 0x0.
Operation of the SSM is address mapped. This chapter explains the address mapping of
AIN for ARM920T AMBA test.
11-2
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
AMBA Test Interface
11.2
Entering and exiting AMBA Test
Six test modes exist:
•
functional test
•
PA TAG RAM test
•
instruction MMU test
•
data MMU test
•
instruction cache test
•
data cache test.
The address of the state location is 0x0. A write to this location changes the test mode,
as shown in Table 11-1. An example TIF file is shown in Example 11-1.
Table 11-1 AMBA test modes
Test mode
Write data
Exit test
0x0
Functional test
0x1
PA TAG RAM test
0x2
Instruction MMU test
0x3
Data MMU test
0x4
Instruction cache test
0x5
Data cache test
0x6
Example 11-1 Example TIF (test input file)
;
A
;
W
Address State Location
00000000
Enter Functional Test Mode
00000001
<Body of Functional Test>
;
A
;
W
E
ARM DDI 0151C
Address State Location
00000000
Exit Test Mode
00000000
ZZZZZZZZ
Copyright © 2000, 2001 ARM Limited. All rights reserved.
11-3
AMBA Test Interface
11.3
Functional test
In AMBA functional test mode, the SSM disconnects the functional ARM920T from its
inputs and disables its output drivers. The SSM provides locations that can be accessed
by the tester. There are 9 locations that can be accessed in functional test mode:
•
3 write locations
•
6 read locations.
These are bit-mapped to AIN[10:2] as shown in Table 11-2.
Note
TAPID[31:0] and ETM<name>, the ARM920T Trace Interface Port, are not
accessible in this test mode
Table 11-2 AMBA functional test locations
11-4
AIN
bit
Location
Read/
write
Data
10
CPDIN
Write
31:0
9
A920Inputs
Write
31:0
8
DIN
Write
31:0
7
DOUT
Read
31:0
6
CPDOUT
Read
31:0
5
CPID
Read
31:0
4
A920Status1
Read
21:0
3
A920Status2
Read
31:0
2
AOUT
Read
31:0
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
AMBA Test Interface
The A920Inputs location, shown in Table 11-12 on page 11-16, is constructed as
shown in Table 11-3.
Table 11-3 Construction of A920Inputs location
ARM DDI 0151C
A920 inputs bit
Signal
31
AGNT
30
WAITIN
29
ERRORIN
28
LASTIN
27
BnRES
26
FCLK
25:20
0
19
VINITHI
18
nFIQ
17
nIRQ
16
ISYNC
15:14
CHSDE[1:0]
13:12
CHSEX[1:0]
11
TRACK
10
IEBKPT
9
DEWPT
8
EDBGRQ
7
EXTERN0
6
EXTERN1
5
TCK
4
TDI
3
TMS
Copyright © 2000, 2001 ARM Limited. All rights reserved.
11-5
AMBA Test Interface
Table 11-3 Construction of A920Inputs location (continued)
A920 inputs bit
Signal
2
nTRST
1
SDOUTBS
0
DBGEN
The A920Status1 location, shown in Table 11-2 on page 11-4, is constructed as shown
in Table 11-4.
Table 11-4 Construction of A920Status1 location
11-6
A920Status1
bits
Signal
21
WRITEOUT
20:19
SIZE
18:17
PROT[1:0]
16:15
BURST[1:0]
14
AREQ
13
LOK
12
TRAN
11
ENBA
10
ENBD
9
FCLKOUT
8
CPCLK
7
nCPWAIT
6
nCPMREQ
5
CPPASS
4
CPLATECANCEL
3
CPTBIT
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
AMBA Test Interface
Table 11-4 Construction of A920Status1 location (continued)
A920Status1
bits
Signal
2
nCPTRANS
1
BIGENDOUT
0
INSTREXEC
The A920Status2 location, shown in Table 11-2 on page 11-4, is constructed as shown
in Table 11-5.
Table 11-5 Construction of A920Status2 location
ARM DDI 0151C
A920Status2 bits
Signal
31
DRIVEOUTBS
30
DBGACK
29
ECLK
28:25
IR[3:0]
24
RANGEOUT0
23
RANGEOUT1
22:18
SCREG[4:0]
17:14
TAPSM[3:0]
13
TDO
12
NTDOEN
11
SDIN
10
SHCLK1BS
9
SHCLK2BS
8
ICAPCLKBS
7
ECAPCLKBS
6
PCLKBS
5
TCK1
Copyright © 2000, 2001 ARM Limited. All rights reserved.
11-7
AMBA Test Interface
Table 11-5 Construction of A920Status2 location (continued)
A920Status2 bits
Signal
4
TCK2
3
RSTCLKBS
2
COMMRX
1
COMMTX
0
DBGRQI
You can update and examine the inputs and outputs of the ARM920T on a per-cycle
basis by writing to the input locations and reading from the output locations. The
functional ARM920T is clocked after every sequence of writes. This means that for
every cycle, at least one location must be written to (usually A920Inputs), but no
locations have to be read. A typical AMBA test iterates the sequence:
•
address locations to be written and read
•
write input locations
•
read output locations
•
turnaround vector.
When the locations have been addressed, they are sequenced through in the order shown
in Figure 11-1 on page 11-9.
11-8
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
AMBA Test Interface
IDLE
000000000
Write
CPDIN
Write
A920 inputs
Write
DIN
Read
DOUT
Read
CPDOUT
Read
CPID
Read
A920Status1
Read
A920Status2
Read
AOUT
100000000
010000000
001000000
000100000
000010000
000001000
000000100
000000010
000000001
Figure 11-1 AMBA functional test state machine
11.3.1
Creating an ARM920T AMBA functional test
The steps required to write a TIF (test input format) file are:
1.
Run an assembler program on a model of the ARM920T. You must run the
program in FastBus mode (see FastBus mode on page 5-3). You must also run
TCK synchronously to BCLK, and at least a factor of two slower.
2.
On each rising edge of BCLK you must record the values of ERRORIN,
WAITIN, and LASTIN. On each falling edge of BCLK, you must record the
values of all other inputs and outputs. This binary string of values is called a
vector.
The AMBA functional test header is:
;
A
W
;
A
ARM DDI 0151C
Entering AMBA Functional Test Mode
00000000
00000001
Addressing all locations
000007FC
Copyright © 2000, 2001 ARM Limited. All rights reserved.
11-9
AMBA Test Interface
3.
Repeat the following sequence for n in the range 1 to <number of vectors>:
;
W
;
W
;
W
;
;
R
;
R
;
R
;
R
;
R
;
R
Writing CPDIN of vector n-1
<Data>
Writing ARM920T Inputs of vector n
<Data>
Writing DIN of vector n-1
<Data>
Clocking ARM920T
Reading DOUT of vector n
<Data> FFFFFFFF
Reading CPID of vector n
<Data> FFFFFFFF
Reading CPDOUT of vector n
<Data> FFFFFFFF
Reading ARM920T Status Location 1 of vector n-1
<Data> 003FFCFF
Reading ARM920T Status Location 2 of vector n-1
<Data> 003FFCFF
Reading AOUT of vector n
<Data> FFFFFFFF
The AMBA functional test footer is:
;
A
W
A
E
ARM920T Exiting AMBA Functional Test Mode
00000000
00000000
ZZZZZZZZ
ZZZZZZZZ
For each write and read, <Data> is an 8-character hexadecimal value. For the buses
CPDIN, DIN, DOUT, CPID, CPDOUT, and AOUT this is the vector value. For the
ARM920T inputs location the data is constructed as shown in Table 11-3 on page 11-5.
For the A920status1 and A920status2 locations, the read data is constructed as shown
in Table 11-4 on page 11-6 and Table 11-5 on page 11-7. Vector number zero does not
exist in the vector file, so on the first iteration you must write CPDIN as zero and you
must give both status locations a mask value of zero. For more information see the
AMBA Specification (Rev 2.0).
Note
If DOUT has the same value on two or more successive vectors, the mask value for the
second and subsequent reads must be zero. It is recommended that you mask out
FCLKOUT and CPCLK in each status1 read.
11-10
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
AMBA Test Interface
11.4
Burst operations
In all test modes other than functional test, the SSM provides locations for burst reads
and writes of certain lengths. These are shown in Table 11-6.
Table 11-6 Burst locations
Burst size
Address
1
0x000
2
0x040
4
0x080
8
0x0C0
16
0x100
32
0x140
64
0x180
128
0x1C0
To construct the address of a location for a burst access, you must add the address of the
burst size to the address of the location. For example:
•
address of PA TAG RAM read location = 0x18
•
address of burst-64 location = 0x180
•
address of burst of 64 PA TAG RAM reads = 0x18 + 0x180 = 0x198.
For each of the six test modes (see Table 11-1 on page 11-3) there is a table
summarizing for each location:
•
its address
•
whether it is for reading or writing
•
whether burst accesses are supported to that location
•
the alignment of read and write data.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
11-11
AMBA Test Interface
11.5
PA TAG RAM test
PA TAG RAM test mode allows you to test reading and writing the memory array. The
memory array comprises eight segments out of a possible 128. Each segment comprises
64 lines. Each line is 26 bits wide. Before either a read or write can be executed, the
segment and index locations must be written, defining the array entry. If this has been
done, writing is achieved as a two-step process and reading as a one-step process.
1.
You must write a data pattern to a test location provided by the SSM.
2.
The data pattern is written into the RAM array and the index is incremented.
Depending on the write location used the data pattern is either incremented or
inverted. For a burst access, the second step is repeated.
There are five write locations and one read location. These are shown in Table 11-7.
Table 11-7 PA TAG RAM locations
Location
Address
Read/
write
Burst
Data
Index
0x04
Write
No
5:0
Segment
0x08
Write
No
6:0
Data pattern
0x0C
Write
No
25:0
RAM write, invert data pattern and
increment index
0x10
Write
Yes
-
RAM write, increment data pattern and
increment index
0x14
Write
Yes
-
RAM read and increment index
0x18
Read
Yes
31:6
When writing the data pattern, the write data is constructed as shown in Table 11-8.
Table 11-8 Construction of data pattern write data
11-12
Data pattern bits
Write data bits
25:21
28:24
20:14
22:16
13:7
14:8
6:0
6:0
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
AMBA Test Interface
For example:
•
data pattern = 0x03FFFFFF
•
write data = 0x1F7F7F7F.
Figure 11-2 shows the write data format.
31
29 28
24 23 22
0 0 0 Data [25:21]
0
16 15 14
Data [20:14]
0
8 7 6
Data [13:7]
0
0
Data [6:0]
Figure 11-2 Write data format
An example sequence to test lines 5 to 8 of memory segment 1 comprises:
1.
Enter PA TAG test mode.
2.
Write index = 5.
3.
Write segment = 1.
4.
Write data pattern = 0.
5.
Burst-4 RAM write and increment both data pattern and index.
6.
Write index = 5.
7.
Burst-4 RAM read and increment index.
8.
Exit test mode.
The TIF file equivalent of the above sequence is:
;
A
W
;
A
W
;
A
W
;
A
W
;
;
A
ARM DDI 0151C
PATAGRAM testmode
00000000
00000002
load index counter 5
00000004
00000005
load segment number 1
00000008
00000001
load data pattern 0
0000000C
00000000
ramwrite, increment data pattern and index, burst of 4
0x14 + 0x80 = 0x94
00000094
Copyright © 2000, 2001 ARM Limited. All rights reserved.
11-13
AMBA Test Interface
W
;
W
;
W
;
W
;
A
W
;
;
A
R
;
R
;
R
;
R
A
;
A
W
;
E
11-14
00000000
ramwrite
00000000
ramwrite
00000000
ramwrite
00000000
load index counter 5. Segment is unchanged at 1.
00000004
00000005
ramread, increment index, burst of 4
0x18 + 0x80 = 0x98
00000098
00000000 FFFFFFC0
ramread
00000040 FFFFFFC0
ramread
00000080 FFFFFFC0
ramread
000000C0 FFFFFFC0
ZZZZZZZZ
Exit Test Mode
00000000
00000000
Exiting Test Mode
ZZZZZZZZ.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
AMBA Test Interface
11.6
Cache test
Cache test mode allows you to perform the following functions:
•
read and write CAM and RAM
•
CAM matches
•
dirty all entries
•
write the lockdown pointer
•
invalidate either the whole cache or a single entry by VA.
Cache test locations that you can access are shown in Table 11-9. See Chapter 2
Programmer’s Model and Appendix B CP15 Test Registers for more details of the
registers used for cache test.
Table 11-9 Cache test locations
Location
Address
Read/write
Burst
Data
CAM
0x04
Read/write
Yes
31:0
RAM
0x08
Read/write
Yes
31:0
CAM match, RAM read
0x0C
Write then read
No
31:0
Invalidate all
0x10
Write
No
-
Dirty all
0x14
Write
No
-
Lockdown victim and base
0x18
Write
No
31:2
Invalidate by VA
0x1C
Write
No
31:5
CAM write data is organized as shown in Table 11-10.
Table 11-10 CAM write data
CAM data
Read value
Write value
31:5
[31:8] MVA TAG
[31:8] MVA TAG
[7:6] = Segment [2:1]
[7:5] = Segment [2:0]
[5] = 0
ARM DDI 0151C
4
Valid
Valid
3
Dirty even
Dirty even
Copyright © 2000, 2001 ARM Limited. All rights reserved.
11-15
AMBA Test Interface
Table 11-10 CAM write data (continued)
CAM data
Read value
Write value
2
Dirty odd
Dirty odd
1
Write back
Write back
0
LFSR[6]
0
CAM match write data is organized as shown in Table 11-11.
Table 11-11 CAM match write data
Match write data
Value
31:8
MVA TAG
7:5
Segment
4:2
Word
1:0
SBZ
CAM match read data is organized as shown in Table 11-12.
Table 11-12 CAM match read data
Match read data
Value
31
Cache miss
30
Cache hit
29:0
RAM read data [29:0]
Invalidate by VA write data is organized as shown in Table 11-13.
Table 11-13 Invalidate by VA write data
11-16
Invalidate by VA data
Value
31:8
VA TAG
7:5
Segment
4:0
SBZ
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
AMBA Test Interface
Lockdown victim and base data organization is shown in Table 11-14.
Table 11-14 Lockdown victim and base data
11.6.1
Data
Value
31:26
Index
25:8
SBZ
7:5
Segment
4:2
Word
1:0
SBZ
Behavior of the cache index pointer in AMBA cache test
Writing the lockdown pointer in AMBA cache test mode specifies the segment, index,
and word that are used for all subsequent CAM and RAM operations. The index
increments after CAM reads or writes and RAM reads or writes, but the segment and
word do not change.
11.6.2
RAM read or write
To read or write the RAM in cache segment n, carry out the following sequence:
1.
2.
Write lockdown victim and base with:
•
lockdown value = 0
•
segment = n
•
word = 0.
Burst 64 RAM read/write:
data = RAM data.
3.
ARM DDI 0151C
Repeat steps 1 and 2 seven times, incrementing the word value each time, from 0
to 7.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
11-17
AMBA Test Interface
11.6.3
CAM read or write
To read or write the CAM in cache segment n, carry out the following sequence:
1.
2.
Write lockdown victim and base with:
•
lockdown value = 0
•
segment = n.
Burst 64 CAM read or write:
TAG, segment, valid, dirty even, dirty odd, write back = CAM data.
11.6.4
CAM match, RAM read
To match on a VA and read out the corresponding RAM entry, carry out the following
sequence:
1.
Address the match location.
2.
Write VA comprising:
3.
11-18
•
VA TAG
•
segment
•
word.
Read:
•
cache hit
•
cache miss
•
RAM data.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
AMBA Test Interface
11.7
MMU test
MMU test allows you to test the following:
•
read and write CAM, RAM1, RAM2, DAC, and lockdown pointer
•
invalidate either a whole TLB or a single entry selected by VA
•
CAM match and RAM1 read.
Table 11-15 shows the MMU test locations. See Chapter 2 Programmer’s Model and
Appendix B CP15 Test Registers for more details of the registers used for MMU test.
Table 11-15 MMU test locations
Location
Address
Read/write
Burst
Data
Invalidate by VA
0x04
Write
No
31:10
CAM match, RAM1 read
0x08
Write then read
No
31:0
CAM
0x24
Read/write
Yes
31:0
RAM1
0x28
Read/write
Yes
31:0
RAM2
0x2C
Read/write
Yes
31:0
RAM1, RAM2
0x30
Read/write
Yes
31:0
DAC
0x34
Read/write
No
31:0
Lockdown
0x38
Read/write
No
31:20, 1
Invalidate all
0x3C
Write
No
-
The data format for the DAC and lockdown locations are described in Register 3,
domain access control register on page 2-15 and Register 10, TLB lockdown register on
page 2-22.
Invalidate by VA data is organized as shown in Table 11-16.
Table 11-16 Invalidate by VA data
ARM DDI 0151C
Invalidate by VA data
Value
31:10
VA tag
9:0
SBZ
Copyright © 2000, 2001 ARM Limited. All rights reserved.
11-19
AMBA Test Interface
Match write data is organized as shown in Table 11-17.
Table 11-17 Match write data
Match write data
Value
31:10
VA tag
9:0
SBZ
CAM data is organized as shown in Table 11-18.
Table 11-18 CAM data
CAM data
Value
31:10
VA tag
9:6
Size_C
(see Table 11-19)
5
Valid
4
Preserved
3:0
SBZ
CAM data size encoding is shown in Table 11-19.
Table 11-19 CAM data Size_C encoding
11-20
Copyright © 2000, 2001 ARM Limited. All rights reserved.
Size
Encoding [3:0]
1MB
0b1111
64KB
0b0111
16KB
0b0011
4KB
0b0001
1KB
0b0000
ARM DDI 0151C
AMBA Test Interface
RAM1 data is organized as shown in Table 11-20.
Table 11-20 RAM1 data
RAM 1 data
Value
31:25
SBZ
24
Protection fault
23
Domain fault
22
MMU miss
21:6
Domain, D15:D0
5
Not cachable
4
Not bufferable
3:0
Access permission
bits [3:0]
For RAM1 reads, bits [24:22] are only valid for a match operation. The encoding of
RAM1 data access permission bits is shown in Table 11-21.
Table 11-21 RAM1 data access permission bits
ARM DDI 0151C
Access permission
bits [3:0]
Decoded as
AP [1:0]
0b0001
0b00
0b0010
0b01
0b0100
0b10
0b1000
0b11
Copyright © 2000, 2001 ARM Limited. All rights reserved.
11-21
AMBA Test Interface
RAM2 data is organized as shown in Table 11-22.
Table 11-22 RAM2 data
RAM 2 data
Value
31:10
Physical address TAG
9:6
Size_R2
5:0
SBZ
The encoding of RAM2 data size bits is shown in Table 11-23.
Table 11-23 RAM2 data Size_R2 encoding
11.7.1
Size_R2
Encoding [3:0]
1MB
0b1111
64KB
0b0111
16KB
0b0011
4KB
0b0000
1KB
0b0001
Behavior of the TLB Index pointer in AMBA MMU test
Auto-increment is enabled for CAM and RAM1 reads and writes.
11.7.2
Indexing the RAM2 array
The index pointer to the RAM2 array is a pipelined version of the CAM and RAM1
index pointer. This means that to read from index n in the RAM2 array, you must first
perform an access to index n in either the CAM or RAM1. Because of this, the
composite location RAM1, RAM2 at address 0x30, and the Burst-128 location at
address 0x1C0 are supported.
11-22
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Chapter 12
Instruction Cycle Summary and Interlocks
This chapter gives the instruction cycle times and shows the timing diagrams for
interlock timing. It contains the following sections:
•
About the instruction cycle summary on page 12-2
•
Instruction cycle times on page 12-3
•
Interlocks on page 12-6.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
12-1
Instruction Cycle Summary and Interlocks
12.1
About the instruction cycle summary
All signals quoted in this chapter are ARM9TDMI signals, and are internal to the
ARM920T. In all cases it is assumed that all accesses are from cached regions of
memory.
If an instruction causes an external access, either when prefetching instructions or when
accessing data, the instruction takes more cycles to complete execution. The additional
number of cycles is dependent on the system implementation.
12-2
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Instruction Cycle Summary and Interlocks
12.2
Instruction cycle times
Table 12-1 shows a key to the symbols used in tables in this section.
Table 12-1 Symbols used in tables
Symbol
Meaning
b
The number of busy-wait states during coprocessor accesses
m
Is in the range 0 to 3, depending on early termination (see Multiplier cycle counts
on page 12-5)
n
The number of words transferred in an LDM/STM/LDC/STC
C
Coprocessor register transfer (C-cycle)
I
Internal cycle (I-cycle)
N
Nonsequential cycle (N-cycle)
S
Sequential cycle (S-cycle)
Table 12-2 summarizes the ARM920T instruction cycle counts and bus activity when
executing the ARM instruction set.
Table 12-2 Instruction cycle bus times
Instruction
Cycles
Instruction
bus
Data bus
Comment
Data Op
1
1S
1I
Normal case
Data Op
2
1S+1I
2I
With register controlled shift
LDR
1
1S
1N
Normal case, not loading PC
LDR
2
1S+1I
1N+1I
Not loading PC and following instruction uses
loaded word (1 cycle load-use interlock)
LDR
3
1S+2I
1N+2I
Loaded byte, halfword, or unaligned word used
by following instruction (2 cycle load-use
interlock)
LDR
5
2S+2I+1N
1N+4I
PC is destination register
STR
1
1S
1N
All cases
LDM
2
1S+1I
1S+1I
Loading 1 Register, not the PC
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
12-3
Instruction Cycle Summary and Interlocks
Table 12-2 Instruction cycle bus times (continued)
Instruction
Cycles
Instruction
bus
Data bus
Comment
LDM
n
1S+(n-1)I
1N+(n-1)S
Loading n registers, n > 1, not loading the PC
LDM
n+4
2S+1N+(n+1)I
1N+(n-1)S+4I
Loading n registers including the PC, n > 0
STM
2
1S+1I
1N+1I
Storing 1 Register
STM
n
1S+(n-1)I
1N+(n-1)S
Storing n registers, n > 1
SWP
2
1S+1I
2N
Normal case
SWP
3
1S+2I
2N+1I
Loaded byte used by following instruction
B,BL,BX
3
2S+1N
3I
All cases
SWI, Undefined
3
2S+1N
3I
All cases
CDP
b+1
1S+bI
(1+b)I
All cases
LDC,STC
b+n
1S+(b+n-1)I
bI+1N+(n-1)S
All cases
MCR
b+1
1S+bI
bI+1C
All cases
MRC
b+1
1S+bI
bI+1C
Normal case
MRC
b+2
1S+(b+1)I
(b+I)I+1C
Following instruction uses transferred data
MUL, MLA
2+m
1S+(1+m)I
(2+m)I
All cases
SMULL,UMULL,
3+m
1S+(2+m)I
(3+m)I
All cases
SMLAL,UMLAL
Table 12-3 shows the instruction cycle times from the perspective of the data bus.
Table 12-3 Data bus instruction times
12-4
Instruction
Cycle time
LDR
1N
STR
1N
LDM,STM
1N+(n-1)S
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Instruction Cycle Summary and Interlocks
Table 12-3 Data bus instruction times (continued)
12.2.1
Instruction
Cycle time
SWP
1N+1S
LDC,STC
1N+(n-1)S
MCR,MRC
1C
Multiplier cycle counts
The number of cycles that a multiply instruction takes to complete depends on the
instruction, and on the value of the multiplier-operand. The multiplier-operand is the
contents of the register specified by bits [11:8] of the ARM multiply instructions, or bits
[2:0] of the Thumb multiply instructions:
•
For ARM MUL, MLA, SMULL, SMLAL, and Thumb MUL, m is:
1 if bits [31:8] of the multiplier operand are all 0 or all 1
2 if bits [31:16] of the multiplier operand are all 0 or all 1
3 if bits [31:24] of the multiplier operand are all 0 or all 1
4 otherwise.
•
For ARM UMULL, UMLAL, m is:
1 if bits [31:8] of the multiplier operand are all 0
2 if bits [31:16] of the multiplier operand are all 0
3 if bits [31:24] of the multiplier operand are all 0
4 otherwise.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
12-5
Instruction Cycle Summary and Interlocks
12.3
Interlocks
Pipeline interlocks occur when the data required for an instruction is not available due
to the incomplete execution of an earlier instruction. When an interlock occurs,
instruction fetches stop on the instruction memory interface of the ARM920T. Four
examples are given in:
•
Example 12-1
•
Example 12-2 on page 12-7
•
Example 12-3 on page 12-7
•
Example 12-4 on page 12-9.
Example 12-1 Single load interlock
In this example, the following code sequence is executed:
LDR R0, [R1]
ADD R2, R0, R1
The ADD instruction cannot start until the data is returned from the load. The ADD
instruction therefore, has to delay entering the Execute stage of the pipeline by one
cycle. The behavior on the instruction memory interface is shown in Figure 12-1.
Fldr
Dldr
Fadd
Eldr
Dadd
Mldr
Dadd
Wldr
Eadd
Madd
Wadd
GCLK
InMREQ
IA[31:1]
ID[31:0]
A+4
LDR
A+8
A+C
A+10
A+14
ADD
Figure 12-1 Single load interlock timing
12-6
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Instruction Cycle Summary and Interlocks
Example 12-2 Two cycle load interlock
In this example, the following code sequence is executed:
LDRB R0, [R1,#1]
ADD R2, R0, R1
Now, because a rotation must occur on the loaded data, there is a second interlock cycle.
The behavior on the instruction memory interface is shown in Figure 12-2.
Fldrb
Dldrb
Fadd
Eldrb
Dadd
Mldrb
Dadd
Wldrb
Dadd
Eadd
Madd
Wadd
GCLK
InMREQ
IA[31:1]
A+4
ID[31:0]
LDRB
A+8
A+C
A+10
A+14
ADD
Figure 12-2 Two cycle load interlock
Example 12-3 LDM interlock
In this example, the following code sequence is executed:
LDM R12,{R1-R3}
ADD R2, R2, R1
The LDM takes three cycles to execute in the Memory stage of the pipeline. The ADD is
therefore delayed until the LDM begins its final memory fetch. The behavior of both the
instruction and data memory interfaces is shown in Figure 12-3.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
12-7
Instruction Cycle Summary and Interlocks
Fldmb
Dldmb
Fadd
Eldmb
Dadd
Mldmb
Dadd
Mldmb
Dadd
Mldmb
Eadd
Wldmb
Madd
Wadd
GCLK
InMREQ
IA[31:1]
ID[31:0]
IA+8
IA+4
LDM
IA+C
IA+10
IA+14
ADD
DnMREQ
DA[31:0]
DD[31:0]
DA
DA+4
DA+8
R1
R2
R3
Figure 12-3 LDM interlock
12-8
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Instruction Cycle Summary and Interlocks
Example 12-4 LDM dependent interlock
In this example, the following code sequence is executed:
LDM R12,{R1-R3}
ADD R4, R3, R1
The code is the same code as in example 3, but in this instance the ADD instruction uses
R3. Due to the nature of load multiples, the lowest register specified is transferred first,
and the highest specified register last. Because the ADD is dependent on R3, there must
be another cycle of interlock while R3 is loaded. The behavior on the instruction and
data memory interface is shown in Figure 12-4 on page 12-10.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
12-9
Instruction Cycle Summary and Interlocks
Fldmb
Dldmb
Fadd
Eldmb
Dadd
Mldmb
Mldmb
Dadd
Dadd
Mldmb
Dadd
Wldmb
Eadd
Madd
Wadd
GCLK
InMREQ
IA[31:1]
ID[31:0]
IA+8
IA+4
LDM
IA+C
IA+10
IA+14
ADD
DnMREQ
DA[31:0]
DD[31:0]
DA
DA+4
DA+8
R1
R2
R3
Figure 12-4 LDM dependent interlock
12-10
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Chapter 13
AC Characteristics
This chapter gives the timing diagrams and timing parameters for the ARM920T
processor. It contains the following sections:
•
ARM920T timing diagrams on page 13-2
•
ARM920T timing parameters on page 13-16
•
Timing definitions for the ARM920T Trace Interface Port on page 13-26.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
13-1
AC Characteristics
13.1
ARM920T timing diagrams
The AMBA bus interface of the ARM920T conforms to the AMBA Specification (Rev
2.0). See this document for the relevant timing diagrams.
Figure 13-1 shows the signal parameters for the FCLK timed coprocessor interface.
FCLK
T fclkh
T fclkl
CPCLK
Tfcpkf
T fcpkr
CPID[31:0]
CPDOUT[31:0]
Tfcpidd Tfcpdoutd
Tfcpidh Tfcpdouth
CPnMREQ
nCPTRANS
CPTBIT
Tfcpmreqd Tftransd Tfcptbitd
Tfcpmreqh Tftransh Tfcptbith
CPLATECANCEL
Tfcand
Tfcanh
CPPASS
Tfpasd
Tfpash
nCPWAIT
Tfnwtd
Tfnwth
CHSDE[1:0]
CHSEX[1:0]
Tfchsds Tfchses
Tfchsdh Tfchseh
CPDIN[31:0]
Tfcdns
Tfcdnh
Figure 13-1 ARM920T FCLK timed coprocessor interface
13-2
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
AC Characteristics
Figure 13-2 shows the signal parameters for the BCLK timed coprocessor interface.
BCLK
Tclkh
Tclkl
CPCLK
Tbcpkr
Tbcpkf
CPID[31:0]
CPDOUT[31:0]
Tbcpidd Tbcpdoutd
Tbcpidh Tbcpdouth
CPnMREQ
nCPTRANS
CPTBIT
Tbcpmreqd Tbtransd Tbcptbitd
Tbcpmreqh Tbtransh Tbcptbith
CPLATECANCEL
Tbcand
Tbcanh
CPPASS
Tbpasd
Tbpash
nCPWAIT
Tbnwtd
Tbnwth
CHSDE[1:0]
CHSEX[1:0]
Tbchsds Tbchses
TbchsdhTbchseh
CPDIN[31:0]
Tbcdns
Tbcdnh
Figure 13-2 ARM920T BCLK timed coprocessor interface
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
13-3
AC Characteristics
Figure 13-3 shows the ARM920T FCLK related signal timing.
FCLK
ECLK
Tfekr
Tfekf
Tffkr
T ffkf
FCLKOUT
nFIQ
nIRQ
Tfints
Tfinth
BIGENDOUT
Tfbigd
Tfbigh
Figure 13-3 ARM920T FCLK related signal timing
13-4
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
AC Characteristics
Figure 13-4 shows the ARM920T BCLK related signal timing.
BCLK
ECLK
Tbekr
T bekf
nFIQ
nIRQ
Tbints
Tbinth
BIGENDOUT
Tbbigd
Tbbigh
Figure 13-4 ARM920T BCLK related signal timing
Figure 13-5 shows the SDOUTBS to TDO signal relationship.
SDOUTBS
TDO
Ttdsd
Ttdsh
Figure 13-5 ARM920T SDOUTBS to TDO relationship
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
13-5
AC Characteristics
Figure 13-6 shows the relationship between nTRST and the following signals:
•
COMMRX
•
COMMTX
•
DBGACK
•
DBGRQI
•
DRIVEOUTBS
•
IR[3:0]
•
RANGEOUT0
•
RANGEOUT1
•
RSTCLKBS
•
SCREG[3:0]
•
SDIN
•
TAPSM[3:0]
•
TDO
•
nTDOEN.
nTRST
Signals
Tbrst
Figure 13-6 ARM920T nTRST to other signals relationship
Figure 13-7 on page 13-7 shows the JTAG output signal timing parameters.
13-6
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
AC Characteristics
TCK
Ttckh
Ttckl
TCK1
Ttckr
Ttckf
TCK2
Ttckf
Ttckr
ECAPCLKBS
ICAPCLKBS
PCLKBS
Tcapr
Tcapf
IR[3:0]
SCREG[3:0]
Tirsd
Tirsh
RSTCLKBS
Tbrtd
Tbrth
Tbrtd
Tbrth
nTDOEN
Ttoed
Ttoeh
TDO
Ttdod
Ttdoh
SDIN
Tsdnd
Tsdnh
TAPSM[3:0]
Ttpmd
Ttpmh
SHCLK1BS
Tshkr
Tshkf
SHCLK2BS
Tshkf
Tshkr
Figure 13-7 ARM920T JTAG output signal timing
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
13-7
AC Characteristics
Figure 13-8 shows the JTAG input signal timing parameters.
TCK
TDI
TMS
Tdis
Tdih
Figure 13-8 ARM920T JTAG input signal timing
Figure 13-9 on page 13-8 shows the FCLK related debug output timing parameters.
FCLK
COMMTX
COMMRX
Tfcomd
Tfcomh
DBGACK
Tfdckd
Tfdckh
RANGEOUT0
Tfrg0d
Tfrg0h
RANGEOUT1
Tfrg1d
Tfrg1h
EXTERN0
EXTERN1
Tfexts
Tfexth
Tfdbqs
Tfdbqh
EDBGRQ
Figure 13-9 ARM920T FCLK related debug output timing
13-8
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
AC Characteristics
Figure 13-10 shows the BCLK related debug output timing parameters.
BCLK
COMMTX
COMMRX
Tbcomd
Tbcomh
DBGACK
Tbdckd
Tbdckh
RANGEOUT0
Tbrg0d
Tbrg0h
RANGEOUT1
Tbrg1d
Tbrg1h
EXTERN0
EXTERN1
Tbexts
Tbexth
Tbdbqs
Tbdbqh
EDBGRQ
Figure 13-10 ARM920T BCLK related debug output timing
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
13-9
AC Characteristics
Figure 13-11 shows the TCK related debug output timing parameters.
TCK
ECLK
Ttekf
Ttekr
DBGRQI
Tdgid
Tdgih
Figure 13-11 ARM920T TCK related debug output timing
Figure 13-12 shows the EDBGRQ to DBGRQI relationship.
EDBGRQ
DBGRQI
Tedqd
Tedqh
Figure 13-12 ARM920T EDBGRQ to DBGRQI relationship
13-10
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
AC Characteristics
Figure 13-13 shows the DBGEN to output relationship.
DBGEN
RANGEOUT0
RANGEOUT1
Trgen
Figure 13-13 ARM920T DBGEN to output relationship
Figure 13-14 shows the BCLK related Trace Interface Port timing parameters.
BCLK
ETMCLOCK
Tbetmckf
Tbetmckr
ETM<name>
Tbetm<name>h
Tbetm<name>d
Figure 13-14 ARM920T BCLK related Trace Interface Port timing
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
13-11
AC Characteristics
Figure 13-15 shows the FCLK related Trace Interface Port timing parameters.
FCLK
ETMCLOCK
Tfetmckf
Tfetmckr
ETM<name>
Tfetm<name>d
Tfetm<name>h
Figure 13-15 ARM920T FCLK related Trace Interface Port timing
Figure 13-16 shows the BnRES timing.
BCLK
5 cycles minimum
BnRES
Tzero
Tihnres
Tzero
Tisnres
Figure 13-16 ARM920T BnRES timing
You can assert BnRES LOW asynchronously during either BCLK phase, but you must
de-assert it during the BCLK LOW phase. You must keep BnRES asserted for a
minimum of five BCLK cycles to ensure a complete reset of the ARM920T.
13-12
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
AC Characteristics
Figure 13-17 shows the ARM920T ASB slave transfer timing parameters.
BCLK
Tclktstl
Tclktsth
DSEL
Tisdsel
Tihdsel
AIN[11:2]
Tisa
Tiha
WRITEIN
Tiswr
Tihwr
DIN[31:0]
Tisd
Tihd
DOUT[31:0]
Tovd
Tohd
Tovenbd
Tohenbd
Tovwait
Tohwait
ENBD
WAITOUT
ENBA
Tovenba
Tohenba
Figure 13-17 ARM920T ASB slave transfer timing
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
13-13
AC Characteristics
Figure 13-18 and Figure 13-19 on page 13-15 show the ARM920T ASB master transfer
timing parameters.
BCLK
Tclkh
Tclkl
AREQ
Tohareq
Tovareq
AOUT
Tova
Toha
WRITEOUT
Tovwrite
Tohwrite
LOK
Tohlok
Tovlok
PROT[1:0]
Tovprot
Tohprot
Tovsize
Tohsize
SIZE[1:0]
ENBA
Tohenba
Tovenba
Tovenba
Tohenba
DOUT[31:0]
Tovd
Tohd
ENBD
Tovenbd
Tohenbd
DIN[31:0]
Tisd Tihd
Figure 13-18 ARM920T ASB master transfer timing
13-14
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
AC Characteristics
BCLK
Tclkh
Tclkl
AREQ
Tohareq
Tovareq
AGNT
Tisagnt
Tihagnt
TRAN[1:0]
Tovtr
Tohtr
Tovtra
ENBTRAN
Toventr
Tohentr Toventr
Tohentr
BURST[1:0]
Tovbst
Tohbst
ASTB
Tovastb
Tohastb
NCMAHB
Tncmahbd
Tncmahbh
ERRORIN
Tiserr Tiherr
LASTIN
Tislast Tihlast
WAITIN
Tiswait Tihwait
Figure 13-19 ARM920T ASB master transfer timing
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
13-15
AC Characteristics
13.2
ARM920T timing parameters
Table 13-1 shows the ARM920T timing parameters.
Table 13-1 ARM920T timing parameters
Timing parameter
Description
No arcs for CPEN a
No arcs for ERROROUT b
No arcs for ISYNC a
No arcs for LASTOUT b
No arcs for TRACK a
No arcs for VINITHI a
13-16
Tbbigd
BIGENDOUT output delay from BCLK falling
Tbbigh
BIGENDOUT output hold from BCLK falling
Tbcand
CPLATECANCEL output delay from BCLK falling
Tbcanh
CPLATECANCEL output hold from BCLK falling
Tbcdnh
CPDIN[31:0] input hold from BCLK falling
Tbcdns
CPDIN[31:0] input setup to BCLK falling
Tbchsdh
CHSDE[1:0] input hold from BCLK falling
Tbchsds
CHSDE[1:0] input setup to BCLK falling
Tbchseh
CHSEX[1:0] input hold from BCLK falling
Tbchses
CHSEX[1:0] input setup to BCLK falling
Tbcomd
COMMTX/COMMRX output delay from BCLK rising
Tbcomh
COMMTX/COMMRX output hold from BCLK rising
Tbcpdoutd
CPDOUT[31:0] output delay from BCLK falling
Tbcpdouth
CPDOUT[31:0] output hold from BCLK falling
Tbcpidd
CPID[31:0] output delay from BCLK falling
Tbcpidh
CPID[31:0] output hold from BCLK falling
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
AC Characteristics
Table 13-1 ARM920T timing parameters (continued)
ARM DDI 0151C
Timing parameter
Description
Tbcpkf
CPCLK falling output delay from BCLK falling
Tbcpkr
CPCLK rising output delay from BCLK rising
Tbcpmreqd
nCPMREQ output delay from BCLK falling.
Tbcpmreqh
nCPMREQ output hold from BCLK falling
Tbcptbitd
CPTBIT output delay from BCLK falling.
Tbcptbith
CPTBIT output hold from BCLK falling
Tbdbqh
EDBGRQ input hold from BCLK falling
Tbdbqs
EDBGRQ input setup to BCLK falling
Tbdckd
DBGACK output delay from BCLK rising
Tbdckh
DBGACK output hold from BCLK rising
Tbdwph
DEWPT input hold from BCLK rising c
Tbdwps
DEWPT input setup to BCLK rising c
Tbekf
ECLK falling output delay from BCLK falling
Tbekr
ECLK rising output delay from BCLK rising
Tbexth
EXTERN0/EXTERN1 input hold from BCLK falling
Tbexts
EXTERN0/EXTERN1 input setup to BCLK falling
Tbibkh
IEBKPT hold after BCLK rising c
Tbibks
IEBKPT input setup to BCLK rising c
Tbinth
nFIQ/nIRQ input hold from BCLK falling
Tbints
nFIQ/nIRQ input setup to BCLK falling
Tbinxd
INSTREXEC output delay from BCLK falling c
Tbinxh
INSTREXEC output hold from BCLK falling c
Tbnwtd
nCPWAIT output delay from BCLK rising
Tbnwth
nCPWAIT output hold from BCLK rising
Copyright © 2000, 2001 ARM Limited. All rights reserved.
13-17
AC Characteristics
Table 13-1 ARM920T timing parameters (continued)
13-18
Timing parameter
Description
Tbpasd
CPPASS output delay from BCLK rising
Tbpash
CPPASS output hold from BCLK rising
Tbrg0d
RANGEOUT0 output delay from BCLK falling
Tbrg0h
RANGEOUT0 output hold from BCLK falling
Tbrg1d
RANGEOUT1 output delay from BCLK falling
Tbrg1h
RANGEOUT1 output hold from BCLK falling
Tbrst
COMMRX/COMMTX/DBGACK/DBGRQI/DRIVEOUTBS/
IR[3:0]/RANGEOUT0/RANGEOUT1/RSTCLKBS/
SCREG[3:0]/SDIN/ TAPSM[3:0]/TDO/nTDOEN output delay
from nTRST falling
Tbrtd
RSTCLKBS output delay from TCK
Tbrth
RSTCLKBS hold time from TCK
Tbtransd
nCPTRANS output delay from BCLK falling
Tbtransh
nCPTRANS output hold from BCLK falling
Tcapf
ECAPCLKBS/ICAPCLKBS/PCLKBS falling output delay from
TCK rising
Tcapr
ECAPCLKBS/ICAPCLKBS/PCLKBS rising output delay from
TCK rising
Tclkh
BCLK minimum width HIGH phase
Tclkl
BCLK minimum width LOW phase
Tclktsth
BCLK minimum width HIGH phase in AMBA test mode
Tclktstl
BCLK minimum width LOW phase in AMBA test mode
Tdebugd
COMMRX/COMMTX/DBGACK/DBGRQI/RANGEOUT0/
RANGEOUT1 output delay from TCK when in debug state c
Tdebugh
COMMRX/COMMTX/DBGACK/DBGRQI/RANGEOUT0/
RANGEOUT1 output hold from TCK when in debug state c
Tdgid
DBGRQI output delay from TCK falling
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
AC Characteristics
Table 13-1 ARM920T timing parameters (continued)
ARM DDI 0151C
Timing parameter
Description
Tdgih
DBGRQI output hold from TCK falling
Tdih
TDI/TMS input hold from TCK rising
Tdis
TDI/TMS input setup to TCK rising
Tdrbsd
DRIVEOUTBS output delay from TCK falling c
Tdrbsh
DRIVEOUTBS output hold from TCK falling c
Tedqd
DBGRQI output delay from EDBGRQ rising or falling
Tedqh
DBGRQI output hold from EDBGRQ rising or falling
Tfbigd
BIGENDOUT output delay from FCLK falling
Tfbigh
BIGENDOUT output hold from FCLK falling
Tfcand
CPLATECANCEL output delay from FCLK falling
Tfcanh
CPLATECANCEL output hold from FCLK falling
Tfcdnh
CPDIN[31:0] input hold from FCLK falling
Tfcdns
CPDIN[31:0] input setup to FCLK falling
Tfchsdh
CHSDE[1:0] input hold to FCLK falling
Tfchsds
CHSDE[1:0] input setup to FCLK falling
Tfchseh
CHSEX[1:0] input hold to FCLK falling
Tfchses
CHSEX[1:0] input setup to FCLK falling
Tfclkh
FCLK minimum width HIGH phase
Tfclkl
FCLK minimum width LOW phase
Tfcomd
COMMTX/RX output delay from FCLK rising
Tfcomh
COMMTX/RX output hold from FCLK rising
Tfcpdoutd
CPOUT[31:0] output delay from FCLK falling
Tfcpdouth
CPOUT[31:0] output hold from FCLK falling
Tfcpidd
CPID[31:0] output delay from FCLK falling
Copyright © 2000, 2001 ARM Limited. All rights reserved.
13-19
AC Characteristics
Table 13-1 ARM920T timing parameters (continued)
13-20
Timing parameter
Description
Tfcpidh
CPID[31:0] output hold from FCLK falling
Tfcpkf
CPCLK falling output delay from FCLK falling
Tfcpkr
CPCLK rising output delay from FCLK rising
Tfcpmreqd
nCPMREQ output delay from FCLK falling
Tfcpmreqh
nCPMREQ output hold time from FCLK falling
Tfcptbitd
CPTBIT output delay from FCLK falling
Tfcptbith
CPTBIT output hold time from FCLK falling
Tfdbqh
EDBGRQ input hold from FCLK falling
Tfdbqs
EDBGRQ input setup to FCLK falling
Tfdckd
DBGACK output delay from FCLK rising
Tfdckh
DBGACK output hold from FCLK rising
Tfdwph
DEWPT input hold from FCLK rising c
Tfdwps
DEWPT input setup to FCLK rising c
Tfekf
ECLK falling output delay from FCLK falling
Tfekr
ECLK rising output delay from FCLK rising
Tfexth
EXTERN0/1 output hold after FCLK falling
Tfexts
EXTERN0/1 input setup to FCLK falling
Tffkf
FCLKOUT falling output delay from FCLK falling
Tffkr
FCLKOUT rising output delay from FCLK rising
Tfibkh
IEBKPT input hold from FCLK rising c
Tfibks
IEBKPT input setup to FCLK rising c
Tfinth
nFIQ/nIRQ input hold from FCLK falling
Tfints
nFIQ/nIRQ input setup to FCLK falling
Tfinxd
INSTREXEC output delay from FCLK falling c
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
AC Characteristics
Table 13-1 ARM920T timing parameters (continued)
ARM DDI 0151C
Timing parameter
Description
Tfinxh
INSTREXEC output hold from FCLK falling c
Tfnwtd
nCPWAIT output delay from FCLK rising
Tfnwth
nCPWAIT output hold from FCLK rising
Tfpasd
CPPASS output delay from FCLK rising
Tfpash
CPPASS output hold from FCLK rising
Tfrg0d
RANGEOUT0 output delay from FCLK falling
Tfrg0h
RANGEOUT0 output hold from FCLK falling
Tfrg1d
RANGEOUT1 output delay from FCLK falling
Tfrg1h
RANGEOUT1 output hold from FCLK falling
Tftransd
nCPTRANS output delay from FCLK falling
Tftransh
nCPTRANS output hold time from FCLK falling
Tiha
AIN[11:2] input hold from BCLK rising
Tihagnt
AGNT input hold from BCLK falling
Tihd
DIN[31:0] input hold from BCLK falling
Tihdsel
DSEL input hold from BCLK rising
Tiherr
ERRORIN input hold from BCLK rising
Tihlast
LASTIN input hold from BCLK rising
Tihnres
BnRES input rising hold from BCLK falling
Tihwait
WAITIN input hold from BCLK rising
Tihwr
WRITEIN input hold from BCLK rising
Tirsd
IREG[3:0]/SCREG[3:0] output delay from TCK falling
Tirsh
IREG[3:0]/SCREG[3:0] output hold from TCK falling
Tisa
AIN[11:2] input setup to BCLK falling
Tisagnt
AGNT input setup to BCLK rising
Copyright © 2000, 2001 ARM Limited. All rights reserved.
13-21
AC Characteristics
Table 13-1 ARM920T timing parameters (continued)
13-22
Timing parameter
Description
Tisd
DIN[31:0] input setup to BCLK falling
Tisdsel
DSEL input setup to BCLK falling
Tiserr
ERRORIN input setup to BCLK rising
Tislast
LASTIN input setup to BCLK rising
Tisnres
BnRES input rising setup to BCLK rising
Tiswait
WAITIN input setup to BCLK rising
Tiswr
WRITEIN input setup to BCLK rising
Tncmahbd
NCMAHB output delay from BCLK rising
Tncmahbh
NCMAHB output hold from BCLK rising
Toha
AOUT[31:0] output hold from BCLK rising
Tohareq
AREQ output hold from BCLK rising
Tohastb
ASTB output hold from BCLK rising
Tohbst
BURST[1:0] output hold from BCLK rising
Tohd
DOUT[31:0] output hold from BCLK falling
Tohenba
ENBA output hold from BCLK rising or falling
Tohenbd
ENBD output hold from BCLK falling
Tohensr
ENSR output hold from BCLK rising or falling
Tohentr
ENBTRAN output hold from BCLK rising or falling
Tohlok
LOK output hold from BCLK rising
Tohprot
PROT[1:0] output hold from BCLK rising
Tohsize
SIZE[1:0] output hold from BCLK rising
Tohtr
TRAN[1:0] output hold from BCLK rising
Tohwait
WAITOUT output hold from BCLK falling
Tohwrite
WRITEOUT output hold from BCLK rising
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
AC Characteristics
Table 13-1 ARM920T timing parameters (continued)
ARM DDI 0151C
Timing parameter
Description
Tova
AOUT[31:0] output delay from BCLK rising
Tovareq
AREQ output delay from BCLK rising
Tovastb
ASTB output delay from BCLK rising
Tovbst
BURST[1:0] output delay from BCLK rising
Tovd
DOUT[31:0] output delay from BCLK falling
Tovenba
ENBA output delay from BCLK rising or falling
Tovenbd
ENBD output delay from BCLK falling
Tovensr
ENSR output delay from BCLK rising or falling
Toventr
ENBTRAN output delay from BCLK rising or falling
Tovlok
LOK output delay from BCLK rising
Tovprot
PROT[1:0] output delay from BCLK rising
Tovsize
SIZE[1:0] output delay from BCLK rising
Tovtr
TRAN[1:0] output delay from BCLK rising
Tovtra
TRAN[1:0] output delay from AGNT rising or falling
Tovwait
WAITOUT output delay from BCLK falling
Tovwrite
WRITEOUT output delay from BCLK rising
Trgen
RANGEOUT0/RANGEOUT1 falling output delay from DBGEN
falling
Tsdnd
SDIN output delay from TCK falling
Tsdnh
SDIN output hold from TCK falling
Tshkf
SHCLK1BS falling output delay from TCK falling d
Tshkf
SHCLK2BS falling output delay from TCK rising d
Tshkr
SHCLK1BS rising output delay from TCK rising d
Tshkr
SHCLK2BS rising output delay from TCK falling d
Ttckf
TCK1 falling output delay from TCK falling e
Copyright © 2000, 2001 ARM Limited. All rights reserved.
13-23
AC Characteristics
Table 13-1 ARM920T timing parameters (continued)
13-24
Timing parameter
Description
Ttckf
TCK2 falling output delay from TCK rising e
Ttckh
TCK minimum width HIGH phase
Ttckl
TCK minimum width LOW phase
Ttckr
TCK1 rising output delay from TCK rising e
Ttckr
TCK2 rising output delay from TCK falling e
Ttdod
TDO output delay from TCK falling
Ttdoh
TDO output hold from TCK falling
Ttdsd
TDO output delay from SDOUTBS rising or falling
Ttdsh
TDO output hold from SDOUTBS rising or falling
Ttekf
ECLK falling output delay from TCK falling
Ttekr
ECLK rising output delay from TCK rising
Tticd
COMMRX/COMMTX/DBGACK/DBGRQI/DRIVEOUTBS/
ECAPCLKBS/ECLK/FCLKOUT/ICAPCLKBS/IR[3:0]/
RANGEOUT0/RANGEOUT1/RSTCLKBS/SCREG[3:0]/SDIN/
SHCLK1BS/SHCLK2BS/TAPSM[3:0]/TCK1/TCK2/TDO/
nTDOEN generic output delay from BCLK during AMBA test c
Ttich
COMMRX/COMMTX/DBGACK/DBGRQI/DRIVEOUTBS/
ECAPCLKBS/ECLK/FCLKOUT/ICAPCLKBS/IR[3:0]/
RANGEOUT0/RANGEOUT1/RSTCLKBS/SCREG[3:0]/SDIN/
SHCLK1BS/SHCLK2BS/TAPSM[3:0]/TCK1/TCK2/TDO/
nTDOEN generic output hold from BCLK during AMBA test c
Ttoed
nTDOEN output delay from TCK falling
Ttoeh
nTDOEN output hold from TCK falling
Ttpmd
TAPSM[3:0] output delay from TCK falling
Ttpmh
TAPSM[3:0] output hold from TCK falling
Tzero
BnRES falling setup to BCLK falling f
Tzero
BnRES falling hold from BCLK falling f
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
AC Characteristics
a.
b.
c.
d.
e.
f.
ARM DDI 0151C
It is assumed that this signal is static.
Permanently driven to 0.
This timing parameter is not shown in any diagram in this chapter.
Tshkr is greater than Tshkf to ensure non-overlapping SHCLK1BS and SHCLK2BS.
Ttckr is greater than Ttckf to ensure non-overlapping TCK1 and TCK2.
This parameter is always zero because the timing arcs refer to asynchronous assertion.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
13-25
AC Characteristics
13.3
Timing definitions for the ARM920T Trace Interface Port
Table 13-2 shows the timing parameters of signals used with the ARM920T Trace
Interface Port.
Table 13-2 ARM920T Trace Interface Port timing definitions
13-26
Timing parameter
Description
No arcs for ETMPWRDOWN
-
Tbetmbigendd
ETMBIGEND output delay from BCLK rising
Tbetmbigendh
ETMBIGEND output hold from BCLK rising
Tbetmchsdd
ETMCHSD[1:0] output delay from BCLK rising
Tbetmchsdh
ETMCHSD[1:0] hold from BCLK rising
Tbetmchsed
ETMCHSE[1:0] output delay from BCLK rising
Tbetmchseh
ETMCHSE[1:0] hold from BCLK rising
Tbetmckf
ETMCLOCK falling output delay from BCLK falling
Tbetmckr
ETMCLOCK rising output delay from BCLK rising
Tbetmdabortd
ETMDABORT output delay from BCLK rising
Tbetmdaborth
ETMDABORT output hold from BCLK rising
Tbetmdad
ETMDA[31:0] output delay from BCLK rising
Tbetmdah
ETMDA[31:0] output hold from BCLK rising
Tbetmdbgackd
ETMDBGACK output delay from BCLK rising
Tbetmdbgackh
ETMDBGACK output hold from BCLK rising
Tbetmddd
ETMDD[31:0] output delay from BCLK rising
Tbetmddh
ETMDD[31:0] output hold from BCLK rising
Tbetmdmasd
ETMDMAS[1:0] output delay from BCLK rising
Tbetmdmash
ETMDMAS[1:0] output hold from BCLK rising
Tbetmdmored
ETMDMORE output delay from BCLK rising
Tbetmdmoreh
ETMDMORE output hold from BCLK rising
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
AC Characteristics
Table 13-2 ARM920T Trace Interface Port timing definitions (continued)
ARM DDI 0151C
Timing parameter
Description
Tbetmdnmreqd
ETMDnMREQ output delay from BCLK rising
Tbetmdnmreqh
ETMDnMREQ output hold from BCLK rising
Tbetmdnrwd
ETMDnRW output delay from BCLK rising
Tbetmdnrwh
ETMDnRW output hold from BCLK rising
Tbetmdseqd
ETMDSEQ output delay from BCLK rising
Tbetmdseqh
ETMDSEQ output hold from BCLK rising
Tbetmhivecsd
ETMHIVECS output delay from BCLK rising
Tbetmhivecsh
ETMHIVECS output hold from BCLK rising
Tbetmiabortd
ETMIABORT output delay from BCLK rising
Tbetmiaborth
ETMIABORT output hold from BCLK rising
Tbetmiad
ETMIA[31:1] output delay from BCLK rising
Tbetmiah
ETMIA[31:1] output hold from BCLK rising
Tbetmid15to8d
ETMID15TO8[15:8] output delay from BCLK rising
Tbetmid15to8h
ETMID15TO8[15:8] output hold from BCLK rising
Tbetmid31to24d
ETMID31TO24[31:24] output delay from BCLK rising
Tbetmid31to24h
ETMID31TO24[31:24] output hold from BCLK rising
Tbetminmreqd
ETMInMREQ output delay from BCLK rising
Tbetminmreqh
ETMInMREQ output hold from BCLK rising
Tbetminstrexecd
ETMINSTREXEC output delay from BCLK rising
Tbetminstrexech
ETMINSTREXEC output hold from BCLK rising
Tbetmiseqd
ETMISEQ output delay from BCLK rising
Tbetmiseqh
ETMISEQ output hold from BCLK rising
Tbetmitbitd
ETMITBIT output delay from BCLK rising
Tbetmitbith
ETMITBIT output hold from BCLK rising
Copyright © 2000, 2001 ARM Limited. All rights reserved.
13-27
AC Characteristics
Table 13-2 ARM920T Trace Interface Port timing definitions (continued)
13-28
Timing parameter
Description
Tbetmlatecanceld
ETMLATECANCEL output delay from BCLK rising
Tbetmlatecancelh
ETMLATECANCEL output hold from BCLK rising
Tbetmnwaitd
ETMnWAIT output delay from BCLK rising
Tbetmnwaith
ETMnWAIT output hold from BCLK rising
Tbetmpassd
ETMPASS output delay from BCLK rising
Tbetmpassh
ETMPASS output hold from BCLK rising
Tbetmrngoutd
ETMRNGOUT[1:0] output delay from BCLK rising
Tbetmrngouth
ETMRNGOUT[1:0] hold from BCLK rising
Tfetmbigendd
ETMBIGEND output delay from FCLK rising
Tfetmbigendh
ETMBIGEND output hold from FCLK rising
Tfetmchsdd
ETMCHSD[1:0] output delay from FCLK rising
Tfetmchsdh
ETMCHSD[1:0] output hold from FCLK rising
Tfetmchsed
ETMCHSE[1:0] output delay from FCLK rising
Tfetmchseh
ETMCHSE[1:0] output hold from FCLK rising
Tfetmckf
FETMCLOCK falling output delay from FCLK falling
Tfetmckr
FETMCLOCK rising output delay from FCLK rising
Tfetmdabortd
ETMDABORT output delay from FCLK rising
Tfetmdaborth
ETMDABORT output hold from FCLK rising
Tfetmdad
ETMDA[31:0] output delay from FCLK rising
Tfetmdah
ETMDA[31:0] output hold from FCLK rising
Tfetmdbgackd
ETMDBGACK output delay from FCLK rising
Tfetmdbgackh
ETMDBGACK output hold from FCLK rising
Tfetmddd
ETMDD[31:0] output delay from FCLK rising
Tfetmddh
ETMDD[31:0] output hold from FCLK rising
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
AC Characteristics
Table 13-2 ARM920T Trace Interface Port timing definitions (continued)
ARM DDI 0151C
Timing parameter
Description
Tfetmdmasd
ETMDMAS[1:0] output delay from FCLK rising
Tfetmdmash
ETMDMAS[1:0] output hold from FCLK rising
Tfetmdmored
ETMDMORE output delay from FCLK rising
Tfetmdmoreh
ETMDMORE output hold from FCLK rising
Tfetmdnmreqd
ETMDnMREQ output delay from FCLK rising
Tfetmdnmreqh
ETMDnMREQ output hold from FCLK rising
Tfetmdnrwd
ETMDnRW output delay from FCLK rising
Tfetmdnrwh
ETMDnRW output hold from FCLK rising
Tfetmdseqd
ETMDSEQ output delay from FCLK rising
Tfetmdseqh
ETMDSEQ output hold from FCLK rising
Tfetmhivecsd
ETMHIVECS output delay from FCLK rising
Tfetmhivecsh
ETMHIVECS output hold from FCLK rising
Tfetmiabortd
ETMIABORT output delay from FCLK rising
Tfetmiaborth
ETMIABORT output hold from FCLK rising
Tfetmiad
ETMIA[31:1] output delay from FCLK rising
Tfetmiah
ETMIA[31:1] output hold from FCLK rising
Tfetmid15to8d
ETMID15TO8[15:8] output delay from FCLK rising
Tfetmid15to8h
ETMID15TO8[15:8] output hold from FCLK rising
Tfetmid31to24d
ETMID31TO24[31:24] output delay from FCLK rising
Tfetmid31to24h
ETMID31TO24[31:24] output hold from FCLK rising
Tfetminmreqd
ETMInMREQ output delay from FCLK rising
Tfetminmreqh
ETMInMREQ output hold from FCLK rising
Tfetminstrexecd
ETMINSTREXEC output delay from FCLK rising
Tfetminstrexech
ETMINSTREXEC output hold from FCLK rising
Copyright © 2000, 2001 ARM Limited. All rights reserved.
13-29
AC Characteristics
Table 13-2 ARM920T Trace Interface Port timing definitions (continued)
13-30
Timing parameter
Description
Tfetmiseqd
ETMISEQ output delay from FCLK rising
Tfetmiseqh
ETMISEQ output hold from FCLK rising
Tfetmitbitd
ETMITBIT output delay from FCLK rising
Tfetmitbith
ETMITBIT output hold from FCLK rising
Tfetmlatecanceld
ETMLATECANCEL output delay from FCLK rising
Tfetmlatecancelh
ETMLATECANCEL output hold from FCLK rising
Tfetmnwaitd
ETMnWAIT output delay from FCLK rising
Tfetmnwaith
ETMnWAIT output hold from FCLK rising
Tfetmpassd
ETMPASS output delay from FCLK rising
Tfetmpassh
ETMPASS output hold from FCLK rising
Tfetmrngoutd
ETMRNGOUT[1:0] output delay from FCLK rising
Tfetmrngouth
ETMRNGOUT[1:0] output hold from FCLK rising
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Appendix A
Signal Descriptions
This appendix describes the ARM920T signals. It contains the following sections:
•
AMBA signals on page A-2
•
Coprocessor interface signals on page A-5
•
JTAG and TAP controller signals on page A-7
•
Debug signals on page A-10
•
Miscellaneous signals on page A-12
•
ARM920T Trace Interface Port signals on page A-13.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
A-1
Signal Descriptions
A.1
AMBA signals
Table A-1 shows the ARM920T AMBA signals.
Table A-1 AMBA signals
Name
Direction
Description
AGNT
Input
Bus grant. A signal from the bus arbiter to a bus master that indicates that the bus
master is granted the bus when WAITIN is LOW.
AIN[11:2]
Input
Address input bus. Used for addressing the ARM920T processor as a slave during
AMBA test.
AOUT[31:0]
Output
Address output bus. The processor address bus, that is driven by the active bus
master.
AREQ
Output
Bus request. A signal from the bus master to the bus arbiter that indicates that the
ARM920T processor requires the bus.
ASTB
Output
Indicates a non-idle A-TRAN cycle.
BCLK
Input
Bus clock. This clock times all bus transfers. Both the LOW phase and HIGH phase
of BCLK control transfers on the bus.
BnRES
Input
ARM920T processor reset. You can assert BnRES LOW asynchronously during
either BCLK phase, but you must de-assert it during the BCLK LOW phase. You
must keep BnRES asserted for a minimum of five BCLK cycles to ensure a
complete reset of the ARM920T processor.
BURST[1:0]
Output
Burst access. These signals indicate the length of a burst transfer. The encoding is:
00 =no burst or undefined burst length
01= current access is part of a burst of 4-word transfers
10 = current access is part of a burst of 8-word transfers
11 = no burst or undefined burst length.
DIN[31:0]
Input
Data input bus.
DOUT[31:0]
Output
Data output bus.
DSEL
Input
Slave select. This signal is used during test within the AMBA system and allows the
ARM920T processor to be selected and to have test vectors applied to it.
ENBA
Output
Tristate enable for AOUT, WRITEOUT, LOK, PROT, and SIZE onto an AMBA
address bus and AMBA request signals.
ENBD
Output
Tristate enable for DOUT onto an AMBA data bus.
ENBTRAN
Output
Tristate enable for TRAN onto AMBA BTRAN.
A-2
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Signal Descriptions
Table A-1 AMBA signals (continued)
Name
Direction
Description
ENSR
Output
Tristate enable for ERROROUT, LASTOUT, and WAITOUT onto AMBA
response signals.
ERRORIN
Input
Error response. A transfer error is indicated by the selected bus slave using the
ERRORIN signal. When ERRORIN is HIGH, a transfer error has occurred. When
ERRORIN is LOW, the transfer is successful. This signal is also used in
combination with the LASTIN signal to indicate a bus retract operation.
ERROROUT
Output
AMBA ERROR response of the ARM920T slave during AMBA test.
LASTIN
Input
Last response. This signal is driven by the selected bus slave to indicate if the
current transfer must be the last of a burst sequence. When LASTIN is HIGH, the
decoder must allow sufficient time for address decoding. When LASTIN is LOW,
the next transfer can continue a burst sequence.
LASTOUT
Output
AMBA LAST response of the ARM920T slave during AMBA test.
LOK
Output
Locked transfers. When HIGH, this signal indicates that the current transfer, and the
next transfer, are to be indivisible, and that no other bus master must be given access
to the bus. This signal is used by the bus arbiter. Asserted in the same cycle as ASTB
is asserted.
NCMAHB
Output
Noncached more indication for noncached load multiples. When HIGH, this
indicates that more words are to be requested as part of the burst transfer. When
LOW, on the last S-TRAN of the burst, this indicates that the current transfer is the
last word of the burst. It is only valid if AGNT remains asserted throughout the
transfer.
PROT[1:0]
Output
Protection control.These signals provide additional information about a bus access
and are primarily intended for use by a bus decoder when acting as a basic
protection unit. The signals indicate if the transfer is an opcode fetch or data access.
They also indicate if the transfer is a privileged mode or User mode as follows:
PROT[0] 0 = Opcode fetch, 1 = Data access
PROT[1] 0 = User access, 1 = Supervisor access
SIZE[1:0]
Output
Transfer size. These signals indicate the size of the transfer:
10 = word access
01 = half word access
00= byte access
11 = reserved.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
A-3
Signal Descriptions
Table A-1 AMBA signals (continued)
Name
Direction
Description
TRAN[1:0]
Output
Transfer type. These signals indicate the type of the next transaction:
00 = an address-only transfer
01 = a nonsequential transfer
11 = a sequential transfer
01 reserved.
WAITIN
Input
Wait response. This signal is driven by the selected bus slave to indicate if the
current transfer can complete. If WAITIN is HIGH, another bus cycle is required.
If WAITIN is LOW, the transfer completes in the current bus cycle.
WAITOUT
Output
AMBA WAIT response of the ARM920T slave during AMBA test.
WRITEIN
Input
Transfer direction.When HIGH, this signal indicates a write transfer. When LOW,
a read transfer.
WRITEOUT
Output
Transfer direction.When HIGH, this signal indicates a write transfer. When LOW,
a read transfer.
A.1.1
AMBA bus specification
The ARM920T processor has a unidirectional AMBA-compatible bus interface. See the
AMBA Specification (Rev 2.0) for full details.
A-4
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Signal Descriptions
A.2
Coprocessor interface signals
Table A-2 shows the ARM920T coprocessor interface signals.
Table A-2 Coprocessor interface signals
Name
Direction
Description
CHSDE[1:0]
Input
Coprocessor handshake decode. The handshake signals from the Decode stage
of the coprocessor pipeline follower.
CHSEX[1:0]
Input
Coprocessor handshake execute. The handshake signals from the Execute stage
of the coprocessor pipeline follower.
CPCLK
Output
Coprocessor clock. This clock controls the operation of the coprocessor
interface.
CPDOUT[31:0]
Output
Coprocessor data out. The coprocessor data bus for transferring MCR and LDC data
to the coprocessor.
CPDIN[31:0]
Input
Coprocessor data in. The coprocessor data bus for transferring MRC and STC data
from the coprocessor to the ARM920T processor.
CPEN
Input
Coprocessor data out enable. When tied LOW, the CPID and CPDOUT buses
are held stable. When tied HIGH, the CPID and CPDOUT buses are enabled. It
is expected that this pin is used statically.
CPID[31:0]
Output
Coprocessor instruction data. This is the coprocessor instruction data bus used
for transferring instructions to the pipeline follower in the coprocessor.
CPLATECANCEL
Output
Coprocessor late cancel. When a coprocessor instruction is being executed, if
this signal is HIGH during the first Memory cycle, the coprocessor instruction
must be canceled without having updated the coprocessor state.
nCPMREQ
Output
Not coprocessor memory request. When LOW on a rising CPCLK edge and
nCPWAIT LOW, the instruction on CPID enters the Decode stage of the
coprocessor pipeline follower. The second instruction previously in the Decode
stage of the pipeline follower enters its Execute stage.
CPPASS
Output
Coprocessor pass. This signal indicates that there is a coprocessor instruction in
the Execute stage of the pipeline, and it must be executed.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
A-5
Signal Descriptions
Table A-2 Coprocessor interface signals (continued)
Name
Direction
Description
CPTBIT
Output
Coprocessor Thumb bit. If HIGH, the coprocessor interface is in Thumb state.
nCPTRANS
Output
Not coprocessor translate. When LOW, the coprocessor interface is in a
nonprivileged mode. When HIGH, the coprocessor interface is in a privileged
mode. The coprocessor samples this signal on every cycle when determining the
coprocessor response.
nCPWAIT
Output
Not coprocessor wait. The coprocessor clock CPCLK is qualified by
nCPWAIT to allow the ARM920T processor to control the transfer of data on
the coprocessor interface. nCPWAIT changes while CPCLK is HIGH.
For more information on the coprocessor interface see Chapter 7 Coprocessor
Interface.
A-6
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Signal Descriptions
A.3
JTAG and TAP controller signals
Table A-3 shows the ARM920T JTAG and TAP controller signals.
Table A-3 JTAG and TAP controller signals
Name
Direction
Description
DRIVEOUTBS
Output
Boundary scan cell enable. This signal controls the multiplexors in the scan cells of an
external boundary scan chain. This signal changes in the UPDATE-IR state when scan
chain 3 is selected, and either the INTEST, EXTEST, CLAMP, or CLAMPZ
instruction is loaded. If you do not connect an external boundary scan chain, you must
leave this output unconnected.
ECAPCLKBS
Output
Extest capture clock for boundary scan. This is a TCK2 wide pulse generated when
the TAP controller state machine is in the CAPTURE-DR state, the current instruction
is EXTEST, and scan chain 3 is selected. This signal captures the chip-level inputs
during EXTEST. If you do not connect an external boundary scan chain, you must
leave this output unconnected.
ICAPCLKBS
Output
Intest capture clock. This is a TCK2 wide pulse generated when the TAP controller
state machine is in the CAPTURE-DR state, the current instruction is INTEST, and
scan chain 3 is selected. This signal captures the chip-level outputs during INTEST. If
you do not connect an external boundary scan chain, you must leave this output
unconnected.
IR[3:0]
Output
Tap controller instruction register. These four bits reflect the current instruction loaded
into the TAP controller instruction register. The bits change on the falling edge of TCK
when the state machine is in the UPDATE-IR state.
PCLKBS
Output
Boundary scan update clock. This is a TCK2 wide pulse generated when the TAP
controller state machine is in the UPDATE-DR state, and scan chain 3 is selected. This
signal is used by an external boundary scan chain as the update clock. If you do not
connect an external boundary scan chain, you must leave this output unconnected.
RSTCLKBS
Output
Boundary scan reset clock. This signal denotes that either the TAP controller state
machine is in the RESET state, or that nTRST has been asserted. You can use this to
reset external boundary scan cells.
SCREG[4:0]
Output
Scan chain register. These five bits reflect the ID number of the scan chain currently
selected by the TAP controller. These bits change on the falling edge of TCK when the
TAP state machine is in the UPDATE-DR state.
SDIN
Output
Boundary scan serial input data. This signal contains the serial data to be applied to an
external scan chain, and is valid around the falling edge of TCK.
SDOUTBS
Input
Boundary scan serial output data. This is the serial data out of the boundary scan chain
(or other external scan chain). It must be set up to the rising edge of TCK. If you do
not connect an external boundary scan chain, you must tie this input LOW.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
A-7
Signal Descriptions
Table A-3 JTAG and TAP controller signals (continued)
Name
Direction
Description
SHCLK1BS
Output
Boundary scan shift clock phase 1. This control signal eases the connection of an
external boundary scan chain. SHCLK1BS clocks the master half of the external scan
cells. When in the SHIFT-DR state of the state machine and scan chain 3 is selected,
SHCLK1BS follows TCK1. When not in the SHIFT-DR state, or when scan chain 3
is not selected, this clock is LOW. If you do not connect an external boundary scan
chain, you must leave this output unconnected.
SHCLK2BS
Output
Boundary scan shift clock phase 2. This control signal eases the connection of an
external boundary scan chain. SHCLK2BS clocks the slave half of the external scan
cells. When in the SHIFT-DR state of the state machine and scan chain 3 is selected,
SHCLK2BS follows TCK2. When not in the SHIFT-DR state, or when scan chain 3
is not selected, this clock is LOW. If you do not connect an external boundary scan
chain, you must leave this output unconnected.
TAPID[31:0]
Input
This is the ARM920T device identification (ID) code test data register, accessible from
the scan chains. You must tie this to an appropriate value when you instantiate the
device:
31:28 Functionality revision
27:12 Product code
11:1 Manufacturer identity
0 IEEE specified = 1.
TAPSM[3:0]
Output
TAP controller state machine. This bus reflects the current state of the TAP controller
state machine. These bits change off the rising edge of TCK.
TCK
Input
Test clock. The JTAG clock (the test clock).
TCK1
Output
TCK, phase 1. TCK1 is HIGH when TCK is HIGH, although there is a slight phase
lag due to the internal clock non-overlap.
TCK2
Output
TCK, Phase 2. TCK2 is HIGH when TCK is LOW, although there is a slight phase
lag due to the internal clock non-overlap.
TDI
Input
Test data input. JTAG serial input.
TDO
Output
Test data output. JTAG serial output.
A-8
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Signal Descriptions
Table A-3 JTAG and TAP controller signals (continued)
Name
Direction
Description
nTDOEN
Output
Not TDO enable. When HIGH, this signal denotes that serial data is being driven out
on the TDO output. nTDOEN is normally used as an output enable for a TDO pin in
a packaged part.
TMS
Input
Test mode select. TMS selects the state that the TAP controller state machine must
change to.
nTRST
Input
Not test reset. Active LOW reset signal for the boundary scan logic. This pin must be
pulsed or driven LOW to achieve normal device operation, in addition to the normal
device reset (BnRES).
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
A-9
Signal Descriptions
A.4
Debug signals
Table A-4 shows the ARM920T debug signals.
Table A-4 Debug signals
Name
Direction
Description
COMMRX
Output
Communications channel receive. When HIGH, this signal denotes that the comms
channel receive buffer contains data waiting to be read by the processor core.
COMMTX
Output
Communications channel transmit. When HIGH, this signal denotes that the comms
channel transmit buffer is empty.
DBGACK
Output
Debug acknowledge. When HIGH, this signal indicates the ARM is in debug state.
DBGEN
Input
Debug enable. This input signal allows the debug features of the ARM920T processor
to be disabled. This signal must be LOW only when debugging is not required.
DBGRQI
Output
Internal debug request. This signal represents the debug request signal that is presented
to the processor core. This is a combination of EDBGRQ, as presented to the ARM920T
processor, and bit 1 of the debug control register.
DEWPT
Input
External watchpoint. This signal allows external data watchpoints to be implemented.
ECLK
Output
External clock output.
EDBGRQ
Input
External debug request. When driven HIGH, this causes the processor to enter debug
state when execution of the current instruction has completed.
EXTERN0
Input
External input 0. This is an input to watchpoint unit 0 of the EmbeddedICE logic in the
processor, and allows breakpoints or watchpoints to be dependent on an external
condition.
EXTERN1
Input
External input 1. This is an input to watchpoint unit 1 of the EmbeddedICE logic in the
processor, and allows breakpoints or watchpoints to be dependent on an external
condition.
IEBKPT
Input
External breakpoint. This signal allows an external instruction breakpoints to be
implemented.
INSTREXEC
Output
Instruction executed. Indicates that in the previous cycle, the instruction in the Execute
stage of the pipeline passed its condition codes, and has been executed.
A-10
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Signal Descriptions
Table A-4 Debug signals (continued)
Name
Direction
Description
RANGEOUT0
Output
EmbeddedICE rangeout 0. This signal indicates that the EmbeddedICE watchpoint
unit 0 has matched the conditions currently present on the address, data, and control
buses. This signal is independent of the state of the watchpoint unit enable control bit.
RANGEOUT1
Output
EmbeddedICE rangeout 1. This signal indicates that the EmbeddedICE watchpoint
unit 1 has matched the conditions currently present on the address, data, and control
buses. This signal is independent of the state of the watchpoint unit enable control bit.
TRACK
Input
Enable TrackingICE mode. Driving this signal HIGH places the ARM920T processor
into tracking mode for debugging purposes.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
A-11
Signal Descriptions
A.5
Miscellaneous signals
Table A-5 shows the ARM920T miscellaneous signals.
Table A-5 Miscellaneous signals
Name
Direction
Description
BIGENDOUT
Output
Big-endian output. When HIGH, the ARM920T processor is operating in big-endian
configuration. When LOW, it is in little-endian configuration.
FCLKOUT
Output
Buffered version of FCLK input.
FCLK
Input
Fast clock. The fast clock input is used when the ARM920T processor is in the
synchronous or asynchronous clocking mode.
VINITHI
Input
Determines the state of CP15 Register 1 V-Bit in reset. When HIGH, V-Bit is 1 coming
out of reset. When LOW, V-Bit is 0 coming out of reset.
ISYNC
Input
Synchronous interrupts. When HIGH, interrupts must be applied synchronously.
nFIQ
Input
Not fast interrupt request. This is the not fast interrupt request (nFIQ) signal.
nIRQ
Input
Not interrupt request. This is the not interrupt request (nIRQ) signal.
A-12
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Signal Descriptions
A.6
ARM920T Trace Interface Port signals
Table A-6 shows the ARM920T Trace Interface Port signals
Table A-6 Trace signals
ARM DDI 0151C
Name
Direction
ETMBIGEND
Output
The signal driving the ARM9TDMI core
BIGEND/BIGENDIAN input. When HIGH, the
processor treats bytes in memory as big-endian
format. When LOW, memory is treated as
little-endian. This is a static configuration signal.
ETMCHSD[1:0]
Output
The coprocessor handshake decode bus driven into
the ARM9TDMI core.
ETMCHSE[1:0]
Output
The coprocessor handshake execute bus driven into
the ARM9TDMI core.
ETMCLOCK
Output
This clock times all operations in the ETM9. All
outputs change from the rising edge and all inputs
are sampled on the rising edge. The clock can be
stretched in either phase.
ETMDA[31:0]
Output
The processor data MVA bus driven by the
ARM9TDMI core.
ETMDABORT
Output
The Data Abort signal driven into the ARM9TDMI
core. The DABORT signal is used to tell the
processor that the requested data memory access is
not allowed.
ETMDBGACK
Output
The debug acknowledge signal driven by the
ARM9TDMI core. When HIGH this signal
indicates that the ARM9TDMI core is in debug
state.
ETMDD[31:0]
Output
The DD bus driven within the ARM920T processor.
ETMDMAS[1:0]
Output
The data memory access size bus driven by the
ARM9TDMI core. These encode the size of a data
memory access in the following cycle.
ETMDMORE
Output
The data control signal driven by the ARM9TDMI
core. If HIGH at the end of the cycle then the data
memory access is directly followed by a sequential
data memory access.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
A-13
Signal Descriptions
Table A-6 Trace signals (continued)
A-14
Name
Direction
ETMDnMREQ
Output
The data memory request signal driven by the
ARM9TDMI core. If LOW at the end of a cycle
then the processor requires a data memory access in
the following cycle.
ETMDnRW
Output
The data read/write signal driven by the
ARM9TDMI core. If LOW at the end of a cycle
then any data memory access in the following cycle
is a read. If HIGH, then it is a write.
ETMDSEQ
Output
The data sequential address signal driven by the
ARM9TDMI core. If HIGH at the end of the cycle
then any data memory access in the following cycle
is sequential from the last data memory access.
ETMHIVECS
Output
The signal driving the ARM9TDMI core HIVECS
input. When LOW the ARM exception vectors start
at address 0x0000 0000. When HIGH, the ARM
exception vectors start at address 0xFFFF 0000. This
is a static configuration signal.
ETMIA[31:1]
Output
The instruction MVA bus driven by the
ARM9TDMI core.
ETMIABORT
Output
The instruction abort signal driven into the
ARM9TDMI core.
ETMID15To8[15:8]
Output
A section from the ID input bus driven into the
ARM9TDMI core.
ETMID31To24[31:24]
Output
A section from the ID input bus driven into the
ARM9TDMI core.
ETMInMREQ
Output
The InMREQ signal driven by the ARM9TDMI
core. If LOW at the end of the cycle then the
processor requires an instruction memory access
during the following cycle.
ETMINSTREXEC
Output
The INSTREXEC pipeline status signal driven by
the ARM9TDMI core. The instruction executed
signal indicates that the instruction in the Execute
stage of the pipeline follower of the ETM9 has been
executed.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Signal Descriptions
Table A-6 Trace signals (continued)
ARM DDI 0151C
Name
Direction
ETMISEQ
Output
The ISEQ signal driven by the ARM9TDMI core. If
HIGH at the end of the cycle then any instruction
memory access during the following cycle is
sequential from the last instruction memory access.
ETMITBIT
Output
The ITBIT signal driven by the ARM9TDMI core.
When HIGH, denotes that the ARM is in Thumb
state. When LOW, the processor is in ARM state.
This signal is valid with the address.
ETMLATECANCEL
Output
The coprocessor late cancel signal driven by the
ARM9TDMI core. If HIGH during the first memory
cycle of a coprocessor instruction, then the
coprocessor must cancel the instruction without
changing any internal state. This signal is only
asserted in cycles where the previous instruction
accessed memory and a data abort occurred.
ETMPASS
Output
The PASS coprocessor signal driven by the
ARM9TDMI core. This signal indicates that the
instruction in the Execute stage of the pipeline
follower of the ETM9 is executed.
ETMPWRDOWN
Input
When HIGH, indicates that the ETM9 can be
powered down. The ARM920T processor uses this
to stop the ETMCLOCK output. When this
happens all other ETM<name> outputs are held
stable.
ETMRNGOUT[1:0]
Output
The RANGEOUT[1:0] EmbeddedICE signals
driven by the ARM. The EmbeddedICE
RANGEOUT signals indicate that the
corresponding watchpoint unit has matched the
conditions currently present on the address, control
and data buses. These signals are independent of the
state of the enable control bit of the watchpoint unit.
ETMnWAIT
Output
You can stall the ETM9 by driving ETMnWAIT
LOW. It must be held HIGH at all other times.
ETMnWAIT is the nWAIT signal driven into the
ARM9TDMI core.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
A-15
Signal Descriptions
A-16
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Appendix B
CP15 Test Registers
This appendix describes the ARM920T CP15 test registers. It contains the following
sections:
•
About the test registers on page B-2
•
Test state register on page B-3
•
Cache test registers and operations on page B-8
•
MMU test registers and operations on page B-18.
•
StrongARM backwards compatibility operations on page B-30.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
B-1
CP15 Test Registers
B.1
About the test registers
The ARM920T coprocessor 15 (CP15), register 15 (c15) is used to provide additional
device-specific test operations. You can use it to access and control the following:
•
Test state register on page B-3
•
Cache test registers and operations on page B-8
•
MMU test registers and operations on page B-18
•
StrongARM backwards compatibility operations on page B-30.
You must only use these operations for test. The ARM Architecture Reference Manual
describes this register as implementation defined.
The format of the CP15 test operations is:
MCR/MRC
p15,opcode_1,Rd,c15,CRm,opcode_2
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
1 1 1 0
Cond
1 1 1 1
opcode_1
CRn
Rd
1
opcode_2
CRm
L
Figure B-1 CP15 MRC and MCR bit pattern
The L bit distinguishes between an MCR (L = 1) and an MRC (L = 0).
B-2
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
CP15 Test Registers
B.2
Test state register
The test state register is used to modify the behavior of the ARM920T from the default
behavior. At reset, all bits of the test state register are cleared to 0.
You can write bits [12:1] by:
MCR
p15,0,Rd,c15,c0,0
You can read bits [12:0] by:
MRC
p15,0,Rd,c15,c0,0
You can only write bit 0 using scan chain 15 (CP15), selecting the test state register. You
can also access bits[12:1] using the same scan chain, but it is recommended that you
only read and write these using MCR and MRC instructions. The functions of bits in the test
state register are listed in Table B-1.
Table B-1 Test state register
ARM DDI 0151C
Bit
Function or name
Description
12
Disable DCache streaming
0 = Enable DCache streaming
1 = Disable DCache streaming
11
Disable ICache streaming
0 = Enable ICache streaming
1 = Disable ICache streaming
10
Disable DCache linefill
0 = Enable DCache linefills
1 = Disable DCache linefills
9
Disable ICache linefill
0 = Enable ICache linefills
1 = Disable ICache linefills
8
Disable CP15, c1, bits[31:30]
0 = Enable R1
1 = Disable R1
7
iA, StrongARM asynchronous select
6
nF, StrongARM notFastBus select
00 = FastBus mode
01 = Synchronous mode
10 = Reserved
11 = Asynchronousmode
5
D force noncachable
0 = Normal operation
1 = Force noncachable behavior in the
DCache
4
I force noncachable
0 = Normal operation
1 = Force noncachable behavior in the ICache
Copyright © 2000, 2001 ARM Limited. All rights reserved.
B-3
CP15 Test Registers
Table B-1 Test state register (continued)
Bit
Function or name
Description
3
MMU test
0 = Disable auto-increment
1 = Enable auto-increment
2
I miss abort
0 = Enable ITLB hardware page table walks
1 = Disable ITLB hardware page table walks
1
D miss abort
0 = Enable DTLB hardware page table walks
1 = Disable DTLB hardware page table walks
0
CP15 interpret mode
0 = Disable CP15 interpret mode
1 = Enable CP15 interpret mode
MRC (reading) return bits [12:0], with bits [31:13] being unpredictable.
MCR (writing) update bits [12:1]. Bits [31:13] and [0] should be zero.
B.2.1
Bit 12, disable DCache streaming
When set, this bit prevents the DCache from streaming data words to the ARM9TDMI
while the linefill is performed to the cache. The linefill still occurs, but the data word is
returned to the ARM9TDMI at the end of the linefill.
B.2.2
Bit 11, disable ICache streaming
When set, this bit prevents the ICache from streaming instructions to the ARM9TDMI
while the linefill is performed to the cache. The linefill still occurs, but the instruction
is returned to the ARM9TDMI at the end of the linefill.
B.2.3
Bit 10, disable DCache linefill
When set, this bit prevents the DCache from performing a linefill on a DCache miss.
Instead, a single word read is performed from the AMBA ASB interface. The memory
region mapping is unchanged. This mode of operation is required for debug, so that the
memory image, as seen by the ARM9TDMI, can be read in a non-invasive manner.
Cache hits from a cachable region read the data word from the cache, and cache misses
from a cachable region do not cause a linefill, but read a single data word from
memory.You must use the control bit disable DCache linefill instead of D force
noncachable, because D force noncachable does not read from the cache on a cache hit.
B-4
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
CP15 Test Registers
B.2.4
Bit 9, disable ICache linefill
When set, this bit prevents the ICache from performing a linefill on an ICache miss.
Instead, a single word read is performed from the AMBA ASB interface. The memory
region mapping is unchanged. This mode of operation is required for debug so that the
memory image, as seen by the ARM9TDMI, can be read in a non-invasive manner.
Cache hits from a cachable region read the instruction from the cache, and cache misses
from a cachable region do not cause a linefill, but read a single instruction from
memory.You must use the control bit disable ICache linefill instead of I force
noncachable, because I force noncachable does not read from the cache on a cache hit.
B.2.5
Bits [8:6], disable CP15 register 1, iA and nF
These 3 bits allow clock switching code compatibility with the SA110 and SA1100
(StrongARM). The StrongARM implements the following MCR instructions:
MCR
p15,0,Rd,c15,c1,2
; Enable clock switching
MCR
p15,0,Rd,c15,c2,2
; Disable clock switching
These are equivalent to selecting Asynchronous and FastBus clocking modes
respectively. If either of the two StrongARM MCR instructions are executed then disable
R1, bit 8, is set. This prevents the iAcr and nFcr, bit[31:30] in CP15 register 1, from
being used to control clock switching. This is necessary to maintain backwards
compatibility with non-ARMv4T compliant devices, that do not use CP15 register 1 to
select the clock mode.
The following applies:
iA’ = (iAcr AND NOT disable R1) or iA_c15
nF’ = (nFcr AND NOT disable R1) or nF_c15
Table B-2 shows the clocking mode selection.
Table B-2 Clocking mode selection
ARM DDI 0151C
Clocking mode
iA’
nF’
FastBus
0
0
Synchronous
0
1
Reserved
1
0
Asynchronous
1
1
Copyright © 2000, 2001 ARM Limited. All rights reserved.
B-5
CP15 Test Registers
B.2.6
Bit 5, D force noncachable
The cachable behavior for a memory region is determined by the AND of the DCache
enable in CP15 register 1 and the cachable bit of the MMU page table entry:
C = Ccr AND Ctt
Setting the D force noncachable bit effectively forces the C=0. This means all memory
accesses are treated as single memory accesses on the AMBA ASB interface. A write
that hits in the cache updates the cache. A read that hits in the cache is ignored, and the
data read from the AMBA ASB interface does not update the cache.
B.2.7
Bit 4, I force noncachable
The cachable behavior for a memory region is determined by the AND of the ICache
enable in CP15 register 1 and the cachable bit of the MMU page table entry:
C = Icr AND Ctt
Setting the I force noncachable bit effectively forces the C=0. This means all memory
accesses are treated as single memory accesses on the AMBA ASB interface. A read
that hits in the cache is ignored, and the instruction from the AMBA ASB interface does
not update the cache.
B.2.8
Bit 3, MMU test
Setting the MMU test bit enables auto-increment of the TLB index pointer in both
MMUs on CAM and RAM1 reads and writes. If this bit is not set, the TLB index pointer
only increments on RAM1 writes.
B.2.9
Bit 2, I miss abort
When ITLB page table walks are disabled, the ITLB miss causes an Instruction Abort
and indicates a translation fault in the IFSR. The Instruction Abort handler then has to
use a CP15 MCR instruction to write a page table entry to the instruction TLB.It is a
requirement that the ICache and MMU is enabled when you disable hardware page table
walks, otherwise the behavior is unpredictable.
B.2.10
Bit 1, D miss abort
When DTLB page table walks are disabled, the DTLB miss causes a Data Abort and
indicates a translation fault in the DFSR. The Data Abort handler then has to use a CP15
MCR instruction to write a page table entry to the data TLB.It is a requirement that the
DCache and MMU is enabled when you disable hardware page table walks, otherwise
the behavior is unpredictable.
B-6
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
CP15 Test Registers
B.2.11
Bit 0, CP15 interpret mode
This bit is only writable using scan chain 15, selecting register c15.State. This accesses
the whole test state register. Therefore this bit must be written using read-modify-write.
Interpreted mode allows interpreted accesses to take place within the ARM920T
memory system. To do this, the required MCR or MRC instruction word must be shifted into
scan chain 15. A system speed LDR (read) or STR (write) can then be performed on the
ARM9TDMI. CP15 will interpret the LDR or STR by executing the MCR or MRC instruction
held in scan chain 15. In the case of an LDR, the data is returned to the ARM9TDMI. In
the case of a STR, the interpreted MCR or MRC completes with the data from the
ARM9TDMI. You can exit interpreted mode by performing a read-modify-write to scan
chain 15, register c15.State to reset bit 0 to 0.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
B-7
CP15 Test Registers
B.3
Cache test registers and operations
The ICache and DCache are maintained using MCR and MRC instructions to CP15 registers
7 and 9, defined by the ARM v4T programmer’s model. Additional operations are
available using MCR and MRC to CP15 register 15. These operations are combined with
those using registers 7 and 9 to enable testing of the caches entirely in software.
A modified subset of these MCR and MRC instructions is available in AMBA test for
production test. See Chapter 11 AMBA Test Interface.
All MCR and MRC instructions to CP15 are available through the debug scan chains in
CP15 interpret mode. This mode of access is intended to be used with a subset of the
available CP15 MCR and MRC instructions, such that using other than the minimal subset
will cause unpredictable behavior. See Chapter 9 Debug Support.
The register 7 operations are all write-only. They are listed in Table B-3.
Table B-3 Register 7 operations
Cache
Function
I and D, or I, or D
Invalidate cache
I or D
Invalidate single entry using MVA
D
Clean single entry using MVA or index
D
Clean and invalidate single entry using MVA or index
I
Prefetch cache line using MVA
The register 9 operations are read and write. They are listed in Table B-4.
Table B-4 Register 9 operations
B-8
Cache
Function
I or D
Read lockdown base (applies to all cache segments).
I or D
Write victim and lockdown base (applies to all cache segments).
I or D
Write victim for specified segment. This is provided for debug only and is not
specified by ARMv4T.
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
CP15 Test Registers
The register 15 operations are listed in Table B-5.
Table B-5 Register 15 operations
Cache
Function
Rd
Data
I and D, or I, or D
Set dirty all entries
SBZ
-
I and D, or I, or D
CAM read to C15.C.<I or D>
Seg
Tag, Dirty,
Index
I and D, or I, or D
CAM write
Tag, Seg, Dirty
-
I and D, or I, or D
RAM read to C15.C.<I or D>
Seg, Word
Data
I and D, or I, or D
RAM write from C15.C.<I or D>
Seg, Word
-
I and D, or I, or D
CAM match RAM read to reg
C15.C.<I or D>
Tag, Seg, Word
Hit or Miss,
Data
The Harvard architecture allows you to combine all of these operations to operate on
both the ICache and DCache in parallel.
Note
For the CAM Match, RAM Read operation the respective MMU does not perform a
lookup and a cache miss does not cause a linefill.
These register 15 operations are all issued as MCR. In these, Rd defines the address for
the operation. Therefore, the data is either supplied from, or latched into, the CP15.C.I
or CP15.C.D in CP15. These 32 bit registers are accessed with the CP15 MCR and MRC
instructions shown in Table B-6.
Table B-6 CP15 MCR and MRC instructions
Cache
Function
I and D, or I, or D
Write to register CP15.C.<I or D>
I or D
Read from register CP15.C.<I or D>
Again, the Harvard architecture allows the data to be written to both CP15.C.<I and D>
in parallel.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
B-9
CP15 Test Registers
Table B-7 summarizes C7, C9, and C15 operations.
Table B-7 Register 7, 9, and 15 operations
Function
B-10
Rd
Instruction
Invalidate ICache and DCache
SBZ
MCR p15,0,Rd,c7,c7,0
Invalidate ICache
SBZ
MCR p15,0,Rd,c7,c5,0
Invalidate ICache single entry (using MVA)
MVA format
MCR p15,0,Rd,c7,c5,1
Prefetch ICache line (using MVA)
MVA format
MCR p15,0,Rd,c7,c13,1
Invalidate DCache
SBZ
MCR p15,0,Rd,c7,c6,0
Invalidate DCache single entry (using MVA)
MVA format
MCR p15,0,Rd,c7,c6,1
Clean DCache single entry (using MVA)
MVA format
MCR p15,0,Rd,c7,c10,1
Clean and invalidate DCache entry (using MVA)
MVA format
MCR p15,0,Rd,c7,c14,1
Clean DCache single entry (using index)
Index format
MCR p15,0,Rd,c7,c10,2
Clean and invalidate DCache entry (using index)
Index format
MCR p15,0,Rd,c7,c14,2
Drain write buffer a
SBZ
MCR p15,0,Rd,c7,c10,4
Wait for interrupt b
SBZ
MCR p15,0,Rd,c7,c0,4
Read DCache lockdown base
Base
MRC p15,0,Rd,c9,c0,0
Write DCache victim and lockdown base
Victim=Base
MCR p15,0,Rd,c9,c0,0
Write DCache victim
Victim, Seg
MCR p15,0,Rd,c9,c1,0
Read ICache lockdown base
Base
MRC p15,0,Rd,c9,c0,1
Write ICache victim and lockdown base
Victim=Base
MCR p15,0,Rd,c9,c0,1
Write ICache victim
Victim, Seg
MCR p15,0,Rd,c9,c1,1
I set dirty all entries
SBZ
MCR p15,2,Rd,c15,c1,0
D set dirty all entries
SBZ
MCR p15,2,Rd,c15,c2,0
I and D set dirty all entries
SBZ
MCR p15,2,Rd,c15,c3,0
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
CP15 Test Registers
Table B-7 Register 7, 9, and 15 operations (continued)
Function
Rd
Instruction
I CAM read to C15.C.I
Seg
MCR p15,2,Rd,cI5,c5,2
D CAM read to C15.C.D
Seg
MCR p15,2,Rd,c15,c6,2
I CAM read to C15.C.I and
D CAM read to C15.C.D
Seg
MCR p15,2,Rd,c15,c7,2
I CAM write
Tag, Seg, Dirty
MCR p15,2,Rd,c15,c5,6
D CAM write
Tag, Seg, Dirty
MCR p15,2,Rd,c15,c6,6
I and D CAM write
Tag, Seg, Dirty
MCR p15,2,Rd,c15,c7,6
I RAM read to C15.C.I
Seg, Word
MCR p15,2,Rd,c15,c9,2
D RAM read to C15.C.D
Seg, Word
MCR p15,2,Rd,c15,c10,2
I RAM read to C15.C.I and
D RAM read to C15.C.D
Seg, Word
MCR p15,2,Rd,c15,c11,2
I RAM write from C15.C.I
Seg, Word
MCR p15,2,Rd,c15,c9,6
D RAM write from C15.C.D
Seg, Word
MCR p15,2,Rd,c15,c10,6
I RAM write from C15.C.I and
D RAM write from C15.C.D
Seg, Word
MCR p15,2,Rd,c15,c11,6
I CAM match, RAM read to C15.C.I
Tag, Seg, Word
MCR p15,2,Rd,c15,c5,5
D CAM match, RAM read to C15.C.D
Tag, Seg, Word
MCR p15,2,Rd,c15,c6,5
I CAM match, RAM read to C15.C.I and
D CAM match, RAM read to C15.C.D
Tag, Seg, Word
MCR p15,2,Rd,c15,c7,5
Write to C15.C.I
Data
MCR p15,3,Rd,c15,c1,0
Write to C15.C.D
Data
MCR p15,3,Rd,c15,c2,0
Write to C15.C.I and
write to C15.C.D
Data
MCR p15,3,Rd,c15,c3,0
Read from C15.C.I
Data read
MRC p15,3,Rd,c15,c1,0
Read from C15.C.D
Data read
MRC p15,3,Rd,c15,c2,0
a. Stops execution until the write buffer has drained.
b. Stops execution in a LOW power state until an interrupt occurs.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
B-11
CP15 Test Registers
The CAM read format for Rd is shown in Figure B-2.
31
8 7
5 4
Seg
SBZ
0
SBZ
Figure B-2 Rd format, CAM read
The CAM write format for Rd is shown in Figure B-3.
31
8 7
5 4 3 2 1 0
Seg
MVA TAG
V
De
WB
Do SBZ
Figure B-3 Rd format, CAM write
In Figure B-3, bit labels have the following meanings:
V
Valid
De
Dirty even (words [3:0])
Do
Dirty odd (words [7:4])
WB
Writeback.
The RAM read format for Rd is shown in Figure B-4.
31
8 7
5 4
Seg
SBZ
2 1 0
Word
SBZ
Figure B-4 Rd format, RAM read
B-12
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
CP15 Test Registers
The RAM write format for Rd is shown in Figure B-5.
31
8 7
5 4
Seg
SBZ
2 1 0
Word
SBZ
Figure B-5 Rd format, RAM write
The CAM match, RAM read format for Rd is shown in Figure B-6.
31
8 7
5 4
Seg
MVA TAG
2 1 0
Word
SBZ
Figure B-6 Rd format, CAM match RAM read
The CAM read format for data is shown in Figure B-7.
8 7 6 5 4 3 2 1 0
31
Seg
[2:1] 0 V
MVA TAG
De
WB
Do
LFSR[6]
Figure B-7 Data format, CAM read
In AMBA cache test mode, the LFSR for the cache is restricted to increment only on a
CAM read.
The RAM read format for data is shown in Figure B-8.
31
0
RAM data word [31:0]
Figure B-8 Data format, RAM read
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
B-13
CP15 Test Registers
The CAM match, RAM read format for data is shown in Figure B-9.
31 30 29
0
RAM data word [29:0]
Miss
Hit
Figure B-9 Data format, CAM match RAM read
B.3.1
Addressing the CAM and RAM
For the CAM read or write, and RAM read or write operations you must specify the
segment, index, and word (for the RAM operations). See Addressing the 16KB ICache
on page 4-5. The CAM and RAM operations use the value in the victim pointer for that
segment, so you must ensure that the value is written in the victim pointer before any
CAM or RAM operation.
If the MCR write victim and lockdown base is used, then the victim pointer is incremented
after every CAM read or write, and every RAM read or write. If the MCR write victim is
used, then the victim pointer is only incremented after every CAM read or write. This
enables efficient reading or writing of the CAM and RAM for an entire segment. The
write cache victim and lockdown operations are listed in Table B-8.
Table B-8 Write cache victim and lockdown operations
B-14
Operation
Instruction
Write DCache victim and lockdown base
MCR p15,0,Rd,c9,c0,0
Write DCache victim
MCR p15,0,Rd,c9,c1,0
Write ICache victim and lockdown base
MCR p15,0,Rd,c9,c0,1
Write ICache victim
MCR p15,0,Rd,c9,c1,1
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
CP15 Test Registers
The write I or D cache victim and lockdown base format for Rd is shown in
Figure B-10.
31
26 25
0
Index
SBZ
Figure B-10 Rd format, write I or D cache victim and lockdown base
The write I or D cache victim format for Rd is shown in Figure B-11.
31
26 25
8 7
Index
SBZ
5 4
Seg
0
SBZ
Figure B-11 Rd format, write I or D cache victim
There are two other cache test registers that are only accessible using debug scan chain
15. These are C15.C.<I or D>.Ind. These registers are written with the current victim of
the addressed segment whenever an MCR CAM read is executed. This is intended for use
in debug to establish the value of the current victim pointer of each segment before
reading the values of the CAM and RAM, so that the value can be restored afterwards.
See Chapter 9 Debug Support.
Example B-1 shows sample code for performing software test of the D Cache. It
contains typical operations with C15.C.D.
Example B-1 DCache test operations
TAG_LSB
SEG_LSB
VLD_LSB
DE_LSB
DO_LSB
WB_LSB
WORD_LSB
LOCK_LSB
EQU
EQU
EQU
EQU
EQU
EQU
EQU
EQU
0x8
0x5
0x4
0x3
0x2
0x1
0x2
0x1A
;
;
;
;
valid
dirty
dirty
write
bit
even bit
odd bit
back bit
; Load DCache victim and lockdown base with 32
MOV
r0,#32 :SHL: LOCK_LSB
MCR
p15,0,r0,c9,c0,0
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
B-15
CP15 Test Registers
; Do DCache CAM write to seg 7, index 32
LDR
r1,=0x123456
MOV
r0,r1,LSL #TAG_LSB
ORR
r0,r0,#7 :SHL: SEG_LSB
ORR
r0,r0,#1 :SHL: VLD_LSB
ORR
r0,r0,#1 :SHL: DE_LSB
ORR
r0,r0,#1 :SHL: DO_LSB
ORR
r0,r0,#1 :SHL: WB_LSB
MCR
p15,2,r0,c15,c6,6
; CAM Tag
;
;
;
;
;
;
Segment
Valid bit
Dirty even bit
Dirty odd bit
Writeback bit
CAM write
; Reload DCache lock-down pointer because it will have incremented
MOV
r0,#32 :SHL: LOCK_LSB
MCR
p15,0,r0,c9,c0,0
; Do DCache RAM write to seg 7, index 32, word 6
LDR
r0,=0x89ABCDEF
MCR
p15,3,r0,c15,c2,0
MOV
ORR
MCR
r0,#7 :SHL: SEG_LSB
r0,r0,#6 :SHL: WORD_LSB
p15,2,r0,c15,c10,6
;
;
;
;
;
;
RAM Data
Write RAM data to
C15.C.D
Segment
Word
RAM write from C15.C.D
; Clear C15.C.D to prove that data comes back from DCache
MOV
r0,#0
MCR
p15,3,r0,c15,c2,0
; Write C15.C.D
; Do a CAM match, RAM read to C15.C.D
LDR
r1,=0x123456
MOV
r0,r1,LSL #TAG_LSB
ORR
r0,r0,#7 :SHL: SEG_LSB
ORR
r0,r0,#6 :SHL: WORD_LSB
MCR
p15,2,r0,c15,c6,5
;
;
;
;
TAG
Segment
Word
CAM match, RAM read
; Read C15.C.D and compare with expected data.
; Note that the top 2 bits of the RAM Data returned from the CAM match
; give the Hit and Miss information [31:30] = [Miss,Hit]
MRC
p15,3,r0,c15,c2,0
; Read C15.C.D
; Check the CAM match for a hit
MOV
r2,#0xC0000000
AND
r2,r2,r0
MOV
r3,#0x80000000
CMP
r2,r3
BNE
Fail
B-16
; Mask bits [31:30]
; Hit
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
CP15 Test Registers
; Check the RAM data
MOV
r0,r0,LSL #2
LDR
r1,=0x89ABCDEF
MOV
r1,r1,LSL #2
CMP
r0,r1
BNE
Fail
TEST_PASS
Fail
TEST_FAIL
END
B.3.2
; Remove bits [31:30]
; Expected data
; Remove bits [31:30]
Testing the LFSR
There is an 8-bit LFSR in both the DCache and ICache that is used to provide the
pseudo-random sequence to increment the segment victim counters in random mode.
This is the default setting of the RR bit in CP15 register 1, bit 14.
The LFSR is tested in a controlled manner in AMBA cache test mode. In this mode the
LFSR is reset to its seed value by performing an MCR invalidate all, and is incremented
once by performing a CAM read. For each CAM read, bit 6 of bits[7:0] is sampled onto
bit 0 of the CAM read data.
The by-product of this is that LFSR[6] is sampled for any CAM read, but the LFSR is
clocked freely when not in AMBA cache test mode. See Chapter 11 AMBA Test
Interface.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
B-17
CP15 Test Registers
B.4
MMU test registers and operations
The ITLB and DTLB are maintained using MCR and MRC instructions to CP15 registers 2,
3, 5, 6, 8, and 10, defined by the ARM v4T programmer’s model. Additional operations
are available using MCR and MRC instructions to CP15 register 15. These operations are
combined with those using registers 2, 3, 5, 6, 8, and 10 to enable testing of the TLBs
entirely in software.
A modified subset of these MCR and MRC instructions are available in AMBA test for
production test. See Chapter 11 AMBA Test Interface.
All MCR and MRC instructions to CP15 are available through the debug scan chains in
CP15 Interpret Mode. This mode of access is intended to be used with a subset of the
available CP15 MCR and MRC instructions, so that using other than the minimal subset
causes unpredictable behavior. See Scan chains 4 and 15, the ARM920T memory system
on page 9-31.
The register 2 operations are read and write. They are extended by the register 15
operations to allow individual control of the separate I and D Translation Table Base
(TTB) registers, and are listed in Table B-9.
Table B-9 TTB register operations
B-18
Register
TLB
Function
c2
I and D
Write I and D TTB registers
c2
D
Read D TTB register
c15
I
Write I TTB register
c15
D
Write D TTB register
c15
I
Read I TTB register
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
CP15 Test Registers
The register 3 operations are read and write. They are extended by the register 15
operations to allow individual control of the separate I and D Domain Access Control
(DAC) registers, and are listed in Table B-10.
Table B-10 DAC register operations
Register
TLB
Function
c3
I and D
Write I and D DAC registers
c3
D
Read D DAC register
c15
I
Write I DAC register
c15
D
Write D DAC register
c15
I
Read I DAC register
The register 5 operations are read and write, but the ability to access the I FSR is not
architecturally defined in ARMv4T and is only intended for debug, when testing the
TLB miss mechanism using aborts rather than hardware page table walks. Register 5
operations are listed in Table B-11. The register 15 duplication remains from
ARM920T Rev 0.
Table B-11 FSR register operations
ARM DDI 0151C
Reg
TLB
Function
c5
I or D
Write Fault Status Register (FSR)
c5
I or D
Read FSR
c15
I
Write I FSR
c15
I
Read I FSR
Copyright © 2000, 2001 ARM Limited. All rights reserved.
B-19
CP15 Test Registers
The register 6 operations are read and write. The I TLB is identical to the D TLB, but
the I FAR is not architecturally defined, so the ability to access the I FAR is for
testability only and the MCR and MRC instructions are described by the ARMv4T as being
UNPREDICTABLE. Register 6 operations are listed in Table B-12.
Table B-12 FAR register operations
Reg
TLB
Function
c6
I or D
Write Fault Address Register (FAR)
c6
I or D
Read FAR
The register 8 operations are all write-only. They are listed in Table B-13.
Table B-13 Register 8 operations
Reg
TLB
Function
c8
I and D, or I, or D
Invalidate TLB
c8
I or D
Invalidate single entry using MVA
The register 10 operations are read and write. They are listed in Table B-14.
Table B-14 Register 10 operations
Reg
TLB
Function
c10
I or D
Read victim, lockdown base and preserve bit
c10
I or D
Write victim, lockdown base and preserve bit
The register 15 operations that operate on the CAM, RAM1, and RAM2 are listed in
Table B-15.
Table B-15 CAM, RAM1, and RAM2 register 15 operations
B-20
TLB
Function
Rd
Data
I or D
CAM read to C15.M.<I or D>
SBZ
Tag, Size, V, P
I and D, or I,
or D
CAM write
Tag, Size, V, P
I or D
RAM1 read to C15.M.<I or D>
SBZ
Copyright © 2000, 2001 ARM Limited. All rights reserved.
Protection
ARM DDI 0151C
CP15 Test Registers
Table B-15 CAM, RAM1, and RAM2 register 15 operations (continued)
TLB
Function
Rd
Data
I and D, or I,
or D
RAM1 write
Protection
I or D
RAM2 read to C15.M.<I or D>
SBZ
PA Tag, Size
I and D, or I,
or D
RAM2 write
PA Tag, Size
PA Tag, Size
I or D
CAM match RAM1 read to C15.M.<I
or D>
MVA
Fault, Miss,
Protection
While the ARM920T memory system is a Harvard architecture, the TLBs are accessed
using CData. This means the write operations can be combined to operate on both the I
TLB and D TLB in parallel.
Note
Setting the CP15 register 15 test status register MMU test bit (bit 3) enables
auto-increment of the TLB index pointer in both MMUs on CAM and RAM1 reads and
writes. If this bit is not set, the TLB index pointer only increments on RAM1 writes.
For the CAM match, RAM1 read operation a TLB miss does not cause a page walk.
These register 15 operations are all issued as MCR, which means that the read and match
operations have to be latched into the CP15.M.I or CP15.M.D in CP15. These are 32 bit
registers that are read with the following CP15 MRC instruction:
Read from register CP15.M.<I or D>
Table B-16 summarizes C2, C3, C5, C6, C8, C10, and C15 operations.
Table B-16 Register 2, 3, 5, 6, 8, 10, and 15 operations
Function
ARM DDI 0151C
Rd
Instruction
Read TTB register
TTB
MRC p15,0,Rd,c2,c0,0
Write TTB register
TTB
MCR p15,0,Rd,c2,c0,0
Read domain 15:0 access
control
DAC
MRC p15,0,Rd,c3,c0,0
Write domain 15:0 access
control
DAC
MCR p15,0,Rd,c3,c0,0
Copyright © 2000, 2001 ARM Limited. All rights reserved.
B-21
CP15 Test Registers
Table B-16 Register 2, 3, 5, 6, 8, 10, and 15 operations (continued)
Function
B-22
Rd
Instruction
Read data FSR value
FSR
MRC p15,0,Rd,c5,c0,0
Write data FSR value
FSR
MCR p15,0,Rd,c5,c0,0
Read prefetch FSR value a
FSR
MRC p15,0,Rd,c5,c0,1
Write prefetch FSR value a
FSR
MCR p15,0,Rd,c5,c0,1
Read D FAR
FAR
MRC p15,0,Rd,c6,c0,0
Write D FAR
FAR
MCR p15,0,Rd,c6,c0,0
Read I FAR a
FAR
MRC p15,0,Rd,c6,c0,1
Write I FAR a
FAR
MCR p15,0,Rd,c6,c0,1
Invalidate TLB(s)
SBZ
MCR p15,0,Rd,c8,c7,0
Invalidate I TLB
SBZ
MCR p15,0,Rd,c8,c5,0
Invalidate I TLB single entry
(using MVA)
MVA format
MCR p15,0,Rd,c8,c5,1
Invalidate D TLB
SBZ
MCR p15,0,Rd,c8,c6,0
Invalidate D TLB single entry
(using MVA)
MVA format
MCR p15,0,Rd,c8,c6,1
Read D TLB lockdown
TLB lockdown
MRC p15,0,Rd,c10,c0,0
Write D TLB lockdown
TLB lockdown
MCR p15,0,Rd,c10,c0,0
Read I TLB lockdown
TLB lockdown
MRC p15,0,Rd,c10,c0,1
Write I TLB lockdown
TLB lockdown
MCR p15,0,Rd,c10,c0,1
Read I TTB
TTB
MRC p15,5,Rd,c15,c1,2
Write I TTB
TTB
MCR p15,5,Rd,c15,c1,2
Write D TTB
TTB
MCR p15,5,Rd,c15,c2,2
Read I DAC
DAC
MRC p15,5,Rd,c15,c1,3
Write I DAC
DAC
MCR p15,5,Rd,c15,c1,3
Write D DAC
DAC
MCR p15,5,Rd,c15,c2,3
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
CP15 Test Registers
Table B-16 Register 2, 3, 5, 6, 8, 10, and 15 operations (continued)
Function
Rd
Instruction
Read prefetch FSR value
FSR
MRC p15,5,Rd,c15,c1,5
Write prefetch FSR value
FSR
MCR p15,5,Rd,c15,c1,5
D CAM read to C15.M.D
SBZ
MCR p15,4,Rd,c15,c6,4
I CAM read to C15.M.I
SBZ
MCR p15,4,Rd,c15,c5,4
D CAM write
Tag, Size, V, P
MCR p15,4,Rd,c15,c6,0
I CAM write
Tag, Size, V, P
MCR p15,4,Rd,c15,c5,0
D and I CAM write
Tag, Size, V, P
MCR p15,4,Rd,c15,c7,0
D RAM1 read to C15.M.D
SBZ
MCR p15,4,Rd,c15,c10,4
I RAM 1 read to C15.M.I
SBZ
MCR p15,4,Rd,c15,c9,4
D RAM1 write
Protection
MCR p15,4,Rd,c15,c10,0
I RAM 1 write
Protection
MCR p15,4,Rd,c15,c9,0
D and I RAM1 write
Protection
MCR p15,4,Rd,c15,c11,0
D RAM2 read to C15.M.D
SBZ
MCR p15,4,Rd,c15,c2,5
I RAM2 read to C15.M.I
SBZ
MCR p15,4,Rd,c15,c1,5
D RAM2 write
PA Tag, Size
MCR p15,4,Rd,c15,c2,1
I RAM2 write
PA Tag, Size
MCR p15,4,Rd,c15,c1,1
D and I RAM2 write
PA Tag, Size
MCR p15,4,Rd,c15,c3,1
D CAM match, RAM1 read to
C15.M.D
MVA
MCR p15,4,Rd,c15,c14,4
I CAM match, RAM1 read to
C15.M.I
MVA
MCR p15,4,Rd,c15,c13,4
Read C15.M.D
Data
MRC p15,4,Rd,c15,c2,6
Read C15.M.I
Data
MRC p15,4,Rd,c15,c1,6
a. These MCR and MRC instructions are not architecturally defined in ARMv4T, and are only
intended for testability. Their behavior is described by ARMv4T as being
UNPREDICTABLE.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
B-23
CP15 Test Registers
Figure B-12 shows the format of Rd for CAM writes and data for CAM reads.
10 9
31
6 5 4 3
SIZE_C
MVA TAG
V P
0
SBZ
Figure B-12 Rd format, CAM write and data format, CAM read
In Figure B-12, V is the Valid bit, P is the Preserve bit, and SIZE_C sets the memory
region size. The allowed values of SIZE_C are shown in Table B-17.
Table B-17 CAM memory region size
SIZE_C[3:0]
Memory region size
0b1111
1MB
0b0111
64KB
0b0011
16KB
0b0001
4KB
0b0000
1KB
Figure B-13 shows the format of Rd for RAM1 writes.
31
22 21
SBZ
6 5 4 3
DOMAIN [D15:D0] (one hot encoding)
D15
nC nB
0
AP
D0
Figure B-13 Rd format, RAM1 write
In Figure B-13, AP[3:0] determines the setting of the access permission bits for a
memory region. The allowed values are listed in Table B-18 on page B-25.
B-24
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
CP15 Test Registers
Table B-18 Access permission bit setting
AP[3:0]
Access permission bits
0b1000
0b11
0b0100
0b10
0b0010
0b01
0b0001
0b00
Figure B-14 shows the data format for RAM1 reads.
31
25 24 23 22 21
6 5 4 3
DOMAIN [D15:D0] (one hot encoding)
SBZ
nC nB
0
AP
D0
Prot TLB
fault miss
Domain D15
fault
Figure B-14 Data format, RAM1 read
In Figure B-14, bits [24:22] are only valid for a match operation. In this case the values
listed in Table B-19 apply.
Table B-19 Miss and fault encoding
ARM DDI 0151C
Prot fault
Domain fault
TLB miss
Function
0
0
0
Hit, OK
0
1
0
Hit, domain fault
1
0
0
Hit, protection fault
1
1
0
Hit, protection and domain fault
-
-
1
TLB miss
Copyright © 2000, 2001 ARM Limited. All rights reserved.
B-25
CP15 Test Registers
Figure B-15 shows the Rd format for RAM2 writes, and the data format for RAM2
reads.
10 9
31
6 5
SIZE_R2
PA TAG
0
SBZ
Figure B-15 Rd format, RAM2 write and data format, RAM2 read
In Figure B-15, SIZE_R2 sets the memory region size. The allowed values of SIZE_R2
are shown in Table B-20.
Table B-20 RAM2 memory region size
SIZE_R2[3:0]
Memory region size
0b1111
1MB
0b0111
64KB
0b0011
16KB
0b0000
4KB
0b0001
1KB
Note
The encoding for SIZE_R2 is different from SIZE_C.
B.4.1
Addressing the CAM, RAM1, and RAM2
For the CAM read or write, RAM1 read or write, and RAM2 read or write operations,
you must specify the index. The CAM and RAM1 operations use the value in the victim
pointer, so you must write this before any CAM or RAM1 operation. RAM2 uses a
pipelined version of the victim pointer used for the CAM or RAM1 operation. This
means that to read from index N in the RAM2 array, you must first perform an access
to index N in either the CAM or RAM1.
B-26
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
CP15 Test Registers
The write TLB lockdown operations are listed in Table B-21.
Table B-21 Write TLB lockdown operations
Operation
Instruction
Write D TLB lockdown
MCR p15,0,Rd,c10,c0,0
Write I TLB lockdown
MCR p15,0,Rd,c10,c0,1
The write I or D TLB lockdown format for Rd is shown in Figure B-16.
31
26 25
Base
20 19
1 0
Victim
SBZ
P
Figure B-16 Rd format, write I or D TLB lockdown
Example B-2 shows sample code for performing software test of the DMMU. It
contains typical operations with C15.M.D.
Example B-2 DMMU test operations
LOCK_BASE_LSB
LOCK_VICT_LSB
P_STATE_LSB
P_ENTRY_LSB
VATAG_LSB
VASIZE_LSB
VALID_LSB
DOMAIN8_LSB
DOMAIN_LSB
NCACHE_LSB
NBUFF_LSB
ACCESS_LSB
PATAG_LSB
PASIZE_LSB
EQU
EQU
EQU
EQU
EQU
EQU
EQU
EQU
EQU
EQU
EQU
EQU
EQU
EQU
0x1A
0x14
0x0
0x4
0xA
0x6
0x5
0xE
0x6
0x5
0x4
0x0
0xA
0x7
; Write the DAC so that when doing a RAM1 Read
; bits [24:23] (P-Fault, D-Fault) can be defined
MOV
r0,#0
MCR
p15,0,r0,c3,c0,0
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
B-27
CP15 Test Registers
; Load the DMMU
MOV
ORR
ORR
MCR
lock-down pointer to index 25
r0,#25 :SHL: LOCK_BASE_LSB
r0,r0,#25 :SHL: LOCK_VICT_LSB
r0,r0,#0 :SHL: P_STATE_LSB
p15,0,r0,c10,c0,0
; CAM write to index 25
LDR
r0,=0xAAAAA
MOV
r0,r0,LSL #VATAG_LSB
ORR
r0,r0,#1 :SHL:
VASIZE_LSB
ORR
r0,r0,#1 :SHL: VALID_LSB
ORR
r0,r0,#1 :SHL: P_ENTRY_LSB
MCR
p15,4,r0,c15,c6,0
; Base
; Victim
; Preserve
;
;
;
;
MVA Tag
Size_C
Valid
Preserve
; RAM2 write to index 25
; The RAM2 location pointed to for reads and writes
; is whichever CAM and RAM1 location was last read or written.
LDR
r0,=0x55555
MOV
r0,r0,LSL #PATAG_LSB
; PATAG
ORR
r0,r0,#3 :SHL: PASIZE_LSB
; Size_R2
MCR
p15,4,r0,c15,c2,1
; As CP15 register 15, Test Status Register, MMU Test (bit 3) is not set,
; the victim pointer will only increment after the RAM1 write.
; So RAM1 write to index 25 (Victim increments to 26 after the write)
MOV
r0,#0
ORR
r0,r0,#0 :SHL: DOMAIN8_LSB
; Upper 8 domains
ORR
r0,r0,#1 :SHL: DOMAIN_LSB
; Lower 8 domains
ORR
r0,r0,#1 :SHL: NCACHE_LSB
; nC
ORR
r0,r0,#1 :SHL: NBUFF_LSB
; nB
ORR
r0,r0,#8 :SHL: ACCESS_LSB
MCR
p15,4,r0,c15,c10,0
; Load the DMMU
MOV
ORR
ORR
MCR
lock-down pointer to index 25
r0,#25 :SHL: LOCK_BASE LSB
r0,r0,#25 :SHL: LOCK_VICT_LSB
r0,r0,#0 :SHL: P_STATE_LSB
p15,0,r0,c10,c0,0
; Base
; Victim
; Preserve
; RAM1 read to C15.M.D
MCR
p15,4,r0,c15,c10,4
; Read C15.M.D to r1
MRC
p15,4,r1,c15,c2,6
; RAM2 read to C15.M.D
MCR
p15,4,r0,c15,c2,5
; Read C15.M.D to r3
B-28
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
CP15 Test Registers
MRC
p15,4,r3,c15,c2,6
; CAM match, RAM1 read to C15.M.D
LDR
r0,=0xAAAAA
MOV
r0,r0,LSL #VATAG_LSB
MCR
p15,4,r0,c15,c14,4
; Read C15.M.D to r2
MRC
p15,4,r2,c15,c2,6
; Compare match
LDR
MOV
ORR
CMP
value to read value and RAM2 read value to write value
r4,=0x55555
; Expected RAM2 PA Tag
r4,r4,LSL #PATAG_LSB
r4,r4,#3 :SHL: PASIZE_LSB
r1,r2
; Compare RAM1 read with
; CAM match, RAM1 read
CMPEQ
r3,r4
; Compare RAM2 read with
; expected RAM2
BNE
Fail
TEST_PASS
Fail
ARM DDI 0151C
TEST_FAIL
END
Copyright © 2000, 2001 ARM Limited. All rights reserved.
B-29
CP15 Test Registers
B.5
StrongARM backwards compatibility operations
The following MCR instructions are supported to provide clock switching and MCR wait for
interrupt compatibility with SA110 and SA1100 (StrongARM).
MCR
p15,0,Rd,c15,c1,2
; Enable clock switching
This is equivalent to Asynchronous clocking mode.
MCR
p15,0,Rd,c15,c2,2
; Disable clock switching
This is equivalent to FastBus clocking mode.
MCR
p15,0,Rd,c15,c8,2
; Wait for interrupt
This is equivalent to MCR p15,0,Rd,c7,c0,4.
These three MCR instructions must not be used and are deprecated in ARM architectures
after v4T.
B-30
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Glossary
This glossary describes some of the terms used in this manual. Where terms can have
several meanings, the meaning presented here is intended.
Abort
A mechanism that indicates to a core that it should halt execution of an attempted illegal
memory access. An abort can be caused by the external or internal memory system as a
result of attempting to access invalid instruction or data memory. An abort is classified
as either a prefetch abort, a data abort, or an external abort. See also Data abort,
External abort and Prefetch abort.
Abort model
An abort model is the defined behavior of an ARM processor in response to a Data
Abort exception. Different abort models behave differently with regard to load and store
instructions that specify base register writeback.
ALU
See Arithmetic Logic Unit.
Application Specific
Integrated Circuit
An integrated circuit that has been designed to perform a specific application function.
It can be custom-built or mass-produced.
Arithmetic Logic
Unit
The part of a processor core that performs arithmetic and logic operations.
ARM state
A processor that is executing ARM (32-bit) word-aligned instructions is operating in
ARM state.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
Glossary-1
Glossary
ASIC
See Application Specific Integrated Circuit.
Banked registers
Those physical registers whose use is defined by the current processor mode. The
banked registers are R8 to R14.
Base register
A register specified by a load or store instruction that is used to hold the base value for
the instruction’s address calculation.
Big-endian
Byte ordering scheme in which bytes of decreasing significance in a data word are
stored at increasing addresses in memory. See also Little-endian and Endianness.
Breakpoint
A breakpoint is a mechanism provided by debuggers to identify an instruction at which
program execution is to be halted. Breakpoints are inserted by the programmer to allow
inspection of register contents, memory locations, variable values at fixed points in the
program execution to test that the program is operating correctly. Breakpoints are
removed after the program is successfully tested. See also Watchpoint.
Byte
An 8-bit data item.
Cache
A block of on-chip or off-chip fast access memory locations, situated between the
processor and main memory, used for storing and retreiving copies of often used
instructions and/or data. This is done to greatly reduce the average speed of memory
accesses and so to increase processor performance.
Cache contention
When the number of frequently-used memory cache lines that use a particular cache set
exceeds the set-associativity of the cache. In this case, main memory activity increases
and performance decreases.
Cache hit
A memory access that can be processed at high speed because the instruction or data
that it addresses is already held in the cache.
Cache line index
The number associated with each cache line in a cache set. Within each cache set, the
cache lines are numbered from 0 to (set associativity) -1.
Cache lockdown
To fix a line in cache memory so that it cannot be overwritten. Cache lockdown allows
critical instructions and/or data to be loaded into the cache so that the cache lines
containing them will not subsequently be reallocated. This ensures that all subsequent
accesses to the instructions/data concerned are cache hits, and therefore complete as
quickly as possible.
Cache miss
A memory access that cannot be processed at high speed because the instruction/data it
addresses is not in the cache and a main memory access is required.
CAM
See Content addressable memory.
Central Processing
Unit
The part of a processor that contains the ALU, the registers, and the instruction decode
logic and control circuitry. Also commonly known as the processor core.
Glossary-2
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Glossary
Clock gating
Gating a clock signal for a macrocell with a control signal (such as PWRDOWN) and
using the modified clock that results to control the operating state of the macrocell.
Condition field
A 4-bit field in an instruction that is used to specify a codition under which the
instruction can execute.
Content
addressable
memory
Memory that is identified by its contents. Content addressable memory is used in
CAM-RAM architecture caches to store the tags for cache entries.
Coprocessor
A processor that supplements the main CPU. It carries out additional functions that the
main CPU cannot perform. Usually used for floating-point math calculations, signal
processing, or memory management.
CPU
See Central Processing Unit.
Data Abort
An indication from a memory system to a core that it should halt execution of an
attempted illegal memory access. A data abort is attempting to access invalid data
memory. See also Abort, External abort and Prefetch abort.
Data cache
See DCache.
DCache
A block of on-chip fast access memory locations, situated between the processor and
main memory, used for storing and retreiving copies of often used data. This is done to
greatly reduce the average speed of memory accesses and so to increase processor
performance.
Debugger
A debugging system that includes a program, used to detect, locate, and correct software
faults, together with custom hardware that supports software debugging.
Domain
A collection of sections, large pages and small pages of memory, which can have their
access permissions switched rapidly by writing to the Domain Access Control Register
(CP15 register 3).
Double word
A 64-bit data item. The contents are taken as being an unsigned integer unless otherwise
stated.
EmbeddedICE
The additional JTAG-based hardware provided by debuggable ARM processors to aid
debugging.
Endianness
Byte ordering. The scheme that determines the order in which successive bytes of a data
word are stored in memory. See also Little-endian and Big-endian.
Exception vector
One of a number of fixed addresses in low memory, or in high memory if high vectors
are configured, that contains the first instruction of the corresponding interrupt service
routine.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
Glossary-3
Glossary
External abort
An indication from an external memory system to a core that it should halt execution of
an attempted illegal memory access. An external abort is caused by the external memory
system as a result of attempting to access invalid memory. See also Abort, Data abort
and Prefetch abort
Halfword
A 16-bit data item.
ICache
A block of on-chip fast access memory locations, situated between the processor and
main memory, used for storing and retreiving copies of often used instructions. This is
done to greatly reduce the average speed of memory accesses and so to increase
processor performance.
Instruction cache
See ICache.
Joint Test Action
Group
The name of the organization that developed standard IEEE 1149.1. This standard
defines a boundary-scan architecture used for in-circuit testing of integrated circuit
devices. It is commonly known by the initials JTAG.
JTAG
See Joint Test Action Group.
Little-endian
Byte ordering scheme in which bytes of increasing significance in a data word are stored
at increasing addresses in memory. See also Big-endian and Endianness.
Macrocell
A complex logic block with a defined interface and behavior. A typical VLSI system
will comprise several macrocells (such as an ARM9E-S, an ETM9, and a memory
block) plus application-specific logic.
Prefetch abort
An indication from a memory system to a core that it should halt execution of an
attempted illegal memory access. A prefetch abort can be caused by the external or
internal memory system as a result of attempting to access invalid instruction memory.
See also Data abort, External abort and Abort
Processor
A contraction of microprocessor. A processor includes the CPU or core, plus additional
components such as memory, and interfaces. These are combined as a single macrocell,
that can be fabricated on an integrated circuit.
Region
A partition of instruction or data memory space.
Register
A temporary storage location used to hold binary data until it is ready to be used.
SBO
See Should be one.
SBZ
See Should be zero.
SCREG
The currently selected scan chain number in an ARM TAP controller.
Should be one
Should be written as 1 (or all 1s for bit fields) by software. Writing a 0 will produce
UNPREDICTABLE results.
Glossary-4
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Glossary
Should be zero
Should be written as 0 (or all 0s for bit fields) by software. Writing a 1 will produce
UNPREDICTABLE results.
Tag bits
The index or key field of a CAM entry.
TAP
See Test access port.
Test Access Port
The collection of four mandatory and one optional terminals that form the input/output
and control interface to a JTAG boundary-scan architecture. The mandatory terminals
are TDI, TDO, TMS, and TCK. The optional terminal is TRST.
Thumb state
A processor that is executing Thumb (16-bit) half-word aligned instructions is operating
in Thumb state
UNDEFINED
An instruction that generates an undefined instruction exception.
UNPREDICTABLE
For reads, the data returned when reading from this location is unpredictable. It can have
any value. For writes, writing to this location causes unpredictable behavior, or an
unpredictable change in device configuration. UNPREDICTABLE instructions must
not halt or hang the processor, or any part of the system.
Watchpoint
A watchpoint is a mechanism provided by debuggers to halt program execution when
the data contained by a particular memory address is changed. Watchpoints are inserted
by the programmer to allow inspection of register contents, memory locations, and
variable values when memory is written to test that the program is operating correctly.
Watchpoints are removed after the program is successfully tested. See also Breakpoint.
Word
A 32-bit data item.
ARM DDI 0151C
Copyright © 2000, 2001 ARM Limited. All rights reserved.
Glossary-5
Glossary
Glossary-6
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Index
The items in this index are listed in alphabetical order. The references given are to page numbers.
A
ABSENT 7-7
Access permission 3-2
bits 3-24
Address 2-6
translation 3-6
AHB interface 6-21
Alignment faults 3-21
AMBA signals A-2
AMBA test
burst operations 11-11
cache test mode 11-15
entering and exiting 11-3
functional test mode 11-4
interface 11-2
MMU test mode 11-19
modes 11-3
PA TAG RAM test mode 11-12
ARM7TDMI code compatibility 2-3
ARM9TDMI 1-2
implementation options 2-3
ARM DDI 0151C
ARM920T 1-2
bus interface 6-2
clocking 5-2
connecting to ASB interface 6-5
ARM940T 1-2
ASB 6-3, 6-5
interface, fully compliant 6-5
slave transfers 6-20
B
Base restored data abort model 2-3
Base updated data abort model 2-3
Bidirectional signals 6-5
Block diagram, functional 1-3
Breakpoint 9-5, 9-51
and exception 9-6
timing 9-5
Buffer 6-5
Buffered STM 6-15
Buffered STR 6-14
Burst transfers 6-7
Bus interface 6-2
Busy-wait
abandoned 7-17
interrupted 7-17
Bypass register 9-19
C
Cache
associativity encoding 2-11
cleaning 4-20
coherence 4-17
lockdown register 2-20
operations register 2-17
size encoding 2-11
test mode, AMBA 11-15
test register B-8
type register 2-8
Cached
fetch 6-16
LDM 6-16
LDR 6-16
Copyright © 2000, 2001 ARM Limited. All rights reserved.
Index-1
Index
CDP 7-13
Clock switching 9-43, B-5, B-30
Clocking modes 2-14
Clocks
DCLK 9-42
GCLK 9-42
internally TCK generated clock
9-42
memory clock 9-42
Coarse page table descriptor 3-11
Code compatibility 2-3
Coherence, cache 4-17
Comms channel 9-66
Control register 2-12
Coprocessor
clocking 7-3
external 7-2
handshake encoding 7-8
instructions 7-3
Coprocessor instructions
privileged modes 7-15
Coprocessor interface 7-2
signals A-5
CPU aborts 3-21
CP14 2-2, 7-2
CP15 2-2, 7-2
accessing registers 2-6
debug access 9-33
interpreted access 9-34
MRC and MCR bit pattern 2-7
register map 2-5
test registers B-2
Debug (continued)
entered from Thumb state 9-45
hardware extensions 9-2
instruction register 9-13
interface standard 9-2
request 9-10, 9-52
scan chains 9-23
signals A-10
speed 9-46
state 9-10
status register 9-60
system 9-3
Debug state
actions of ARM920T 9-10
breakpoint and exception 9-6
entry on breakpoint 9-5
entry on debug request 9-10
entry on watchpoint 9-6
exit from 9-48
watchpoint and exception 9-9
Descriptor
coarse page table 3-11
fine page table 3-12
level one 3-8
level two 3-14
section 3-10
Device ID code register 9-19
Dirty data eviction 6-17
Domain 3-2
access control 3-23
access control register 2-15
faults 3-21, 3-26
D
E
Data Abort model 2-3
DCache
enabling and disabling 4-10
operation 4-10
organization 4-4, 4-13
replacement algorithm 4-13
Debug
comms control register 9-64
communications 9-66
communications channel 9-64
control register 9-60
debug scan chain 9-28
entered from ARM state 9-45
EmbeddedICE 9-54
accessing hardware registers 9-29
control registers 9-56
macrocell 9-1
mask registers 9-56
register map 9-54
single stepping 9-63
EmbeddedICE watchpoint units
debugging 9-11
programming 9-11
testing 9-11
ETM interface 8-2
Extension space 2-4
Index-2
External
aborts 3-28
coprocessors 7-2
scan chains 9-21
F
FAR 2-17, 3-22
Fast context switch 2-26
FastBus mode 5-3
Fault
address register 2-17, 3-22
checking 3-25
domain 3-26
permission 3-27
status register 2-16, 3-22
translation 3-26
Fine page table descriptor 3-12
FSR 2-16, 3-22
Functional block diagram 1-3
Functional test 11-4
G
GO 7-7
H
Handshake signals 7-7
Harvard architecture 1-2
I
ICache
operation 4-6
replacement algorithm 4-7
ID code register 2-8
Implementation options 2-3
Instruction cycle
counts and bus activity 12-3
data bus instruction times 12-4
Instruction set extension spaces 2-4
Interlocked MCR 7-11
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
Index
MVA 2-6
Interlocks 12-6
LDM dependent timing 12-9
LDM timing 12-7
single load timing 12-6
two cycle load timing 12-7
N
J
JTAG
and TAP controller signals A-7
interface 9-11
state machine 9-12
Nonbuffered STM 6-15
Nonbuffered STR 6-14
Noncached fetches 6-12
Noncached LDM 6-13
Noncached LDRs 6-12
O
Options, implementation 2-3
Register(continued)
fault status 2-16, 3-22
ID code 2-8
map, CP15 2-5
MMU test B-18
process ID 2-24
scan chain select 9-20
TAP instruction 9-20
test B-2
test configuration 2-26
test state B-3
TLB lockdown 2-22
translation lookaside buffer 2-19
translation table base 2-14, 3-6
Reset, test 9-13
L
Large page references, translating 3-17 P
LAST 7-7
LDC 7-5
PA 2-6
Level one
PA TAG RAM 4-22
descriptor 3-8
debug access 9-39
descriptor, accessing 3-8
Page tables 3-7
fetch 3-8
Page walk 6-20
Level two
PC
cache support 6-23
behavior during debug 9-51
Level two|
return calculation in debug 9-53
descriptor 3-14
Performance analysis 6-23
LFSR testing B-17
Permission faults 3-21, 3-27
Line length encoding 2-12
Physical address 2-6
TAG RAM 4-22
Pipeline interlocks 12-6
Privileged instructions 7-15
M
Process ID register 2-24
Processor state, determining 9-45
MCR 7-9
interlocked 7-11
Memory management unit 3-2
Miscellaneous signals A-12
R
MMU 3-2
enabling 2-14
Register
enabling and disabling 3-29
bypass 9-19
fault checking 3-25
cache lockdown 2-20
faults 3-21
cache operations 2-17
registers 3-4
cache test B-8
MMU test
cache type 2-8
mode 11-19
control 2-12
registers B-18
device ID code 9-19
Modified virtual address 2-6
domain access control 2-15
MRC 7-9
fault address 2-17, 3-22
ARM DDI 0151C
S
Scan chain 9-11, 9-23
controlling external 9-30
external 9-21
multiplexor, external 9-22
number allocation 9-23
select register 9-20
Scan chain 0 9-23
Scan chain 1 9-28
Scan chain 15 9-31, 9-32
Scan chain 2 9-29
Scan chain 3 9-30
Scan chain 4 9-31, 9-39
Scan chain 6 9-31
Section
descriptor 3-10
references, translating 3-13
Serial test and debug 9-12
Signals
AMBA A-2
coprocessor interface A-5
debug A-10
handshake 7-7
JTAG and TAP controller A-7
miscellaneous A-12
trace interface port A-13
Single stepping 9-63
Slave transfers 6-20
Small page references, translating 3-18
STC 7-5
StrongARM B-30
Copyright © 2000, 2001 ARM Limited. All rights reserved.
Index-3
Index
V
Subpages 3-20
Swap 6-18
Swap instructions 4-14
Synchronous mode 5-4
SYSPEED bit 9-47
System speed
access 9-53
instructions 9-47
VA 2-6
Vector catch register 9-61
Vector catching 9-62
Virtual address 2-6
W
T
TAP controller 9-12
TAP instruction register 9-20
Test
configuration register 2-26
data registers 9-19
interface, AMBA 11-2
registers B-2
reset 9-13
state register B-3
Timing
diagrams 13-2
parameters 13-16
Tiny page references, translating 3-19
TLB lockdown register 2-22
TLB operations register 2-19
Trace interface port signals A-13
TrackingICE 10-2
outputs 10-4
Transfer types, ASB 6-6
Translating page tables 3-7
Translation faults 3-21, 3-26
Translation lookaside buffer lockdown
register 2-22
Translation lookaside buffer operations
register 2-19
Translation table base 3-6
register 2-14
TTB 3-6
register 2-14
WAIT 7-7
Watchpoint 9-9, 9-51
and breakpoint 9-52
and exception 9-52
control register 9-57, 9-59
timing 9-7
Write buffer
enabling and disabling 4-10
operation 4-10
Write-back 6-17
U
Unidirectional signals 6-6
Index-4
Copyright © 2000, 2001 ARM Limited. All rights reserved.
ARM DDI 0151C
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