Device Guide - XMC4000 - C-Start and Device Initialization

XMC4000
Microcontroller Series
for Industrial Applications
C- Sta rt an d D e vic e I nitializ a ti on
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Introduction
C-Start tasks
Linker scripts
Execution profiles
Device initialization hints
De vice Gu ide
V1.0 2013-06
Microcontrollers
Edition 2013-06
Published by
Infineon Technologies AG
81726 Munich, Germany
© 2013 Infineon Technologies AG
All Rights Reserved.
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C-Start and Device Initialization
XMC4000 Family
Revision History
Revision History
Page or Item
Subjects (major changes since previous revision)
V1.0, 2013-06
Trademarks of Infineon Technologies AG
AURIX™, C166™, CanPAK™, CIPOS™, CIPURSE™, EconoPACK™, CoolMOS™, CoolSET™,
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SIEGET™, SINDRION™, SIPMOS™, SmartLEWIS™, SOLID FLASH™, TEMPFET™, thinQ!™,
TRENCHSTOP™, TriCore™.
Other Trademarks
Advance Design System™ (ADS) of Agilent Technologies, AMBA™, ARM™, MULTI-ICE™, KEIL™,
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Internationale. IrDA™ of Infrared Data Association Corporation. ISO™ of INTERNATIONAL
ORGANIZATION FOR STANDARDIZATION. MATLAB™ of MathWorks, Inc. MAXIM™ of Maxim
Integrated Products, Inc. MICROTEC™, NUCLEUS™ of Mentor Graphics Corporation. Mifare™ of
NXP. MIPI™ of MIPI Alliance, Inc. MIPS™ of MIPS Technologies, Inc., USA. muRata™ of MURATA
MANUFACTURING CO., MICROWAVE OFFICE™ (MWO) of Applied Wave Research Inc.,
OmniVision™ of OmniVision Technologies, Inc. Openwave™ Openwave Systems Inc. RED HAT™
Red Hat, Inc. RFMD™ RF Micro Devices, Inc. SIRIUS™ of Sirius Satellite Radio Inc. SOLARIS™ of
Sun Microsystems, Inc. SPANSION™ of Spansion LLC Ltd. Symbian™ of Symbian Software Limited.
TAIYO YUDEN™ of Taiyo Yuden Co. TEAKLITE™ of CEVA, Inc. TEKTRONIX™ of Tektronix Inc.
TOKO™ of TOKO KABUSHIKI KAISHA TA. UNIX™ of X/Open Company Limited. VERILOG™,
PALLADIUM™ of Cadence Design Systems, Inc. VLYNQ™ of Texas Instruments Incorporated.
VXWORKS™, WIND RIVER™ of WIND RIVER SYSTEMS, INC. ZETEX™ of Diodes Zetex Limited.
Last Trademarks Update 2011-02-24
C-Start and Device Initialization
XMC4000 Family
Table of Contents
Table of Contents
Revision History .................................................................................................................................................... 3
Table of Contents .................................................................................................................................................. 4
Introduction ............................................................................................................................................................ 6
1
1.1
1.2
1.3
Introduction ........................................................................................................................................ 7
C-Start (also known as CStart/Startup) ................................................................................................ 7
C-Start Packaging ................................................................................................................................ 7
C-Start tasks......................................................................................................................................... 7
C-Start tasks ........................................................................................................................................................... 8
2
2.1
2.2
2.3
2.4
2.5
C-Start tasks ....................................................................................................................................... 9
Device Booting ..................................................................................................................................... 9
Device initialization ............................................................................................................................. 11
Program loading ................................................................................................................................. 12
Giving control to the user application entry point ............................................................................... 14
Default definition of exception and interrupt handlers ........................................................................ 14
Linker scripts ....................................................................................................................................................... 15
3
3.1
3.2
3.3
3.4
3.4.1
Linker scripts .................................................................................................................................... 16
Role of a linker script .......................................................................................................................... 16
Concept of LMA and VMA .................................................................................................................. 16
Typical program section assignment.................................................................................................. 17
Elaboration of GNU linker scripts written for XMC4 devices .............................................................. 19
Examples............................................................................................................................................ 20
Execution profiles ................................................................................................................................................ 21
4
4.1
4.2
4.2.1
4.2.2
4.2.3
4.3
4.3.1
4.3.2
Execution profiles ............................................................................................................................ 22
Execute in Place (XIP) ....................................................................................................................... 22
XIP + Time critical code in volatile memory ....................................................................................... 22
Example: Creating a dedicated section for time-critical code in the linker script ............................... 22
Example: Assigning time critical code to dedicated sections in source code .................................... 23
Example: Program loader modification for loading time critical code to SRAM ................................. 23
Complete code execution from SRAM ............................................................................................... 24
Example: Linker script modification.................................................................................................... 24
Example: Program loader modification .............................................................................................. 25
Device initialization hints .................................................................................................................................... 27
5
5.1
5.2
5.2.1
5.2.2
5.2.3
5.2.4
5.2.5
5.2.6
5.2.7
5.2.8
5.2.9
5.2.10
5.2.11
5.2.12
5.3
5.3.1
Hints on device initialization ........................................................................................................... 28
Timing of device initialization ............................................................................................................. 28
Clock and reset configuration ............................................................................................................. 29
System clock configuration algorithm................................................................................................. 29
Using the backup clock as system clock (fSYS = fOFI) ..................................................................... 30
Using the oscillator clock as system clock (fSYS = fPLL) .................................................................. 30
Downscaling the System clock (fSYS) ............................................................................................... 31
Setting up the oscillator ...................................................................................................................... 31
VCO output configuration and PLL lock ............................................................................................. 32
Target frequency ramp-up .................................................................................................................. 33
CPU clock and peripheral bus clock .................................................................................................. 33
Peripheral clock configuration ............................................................................................................ 34
Peripheral clock control ...................................................................................................................... 34
Clock gating during sleep modes ....................................................................................................... 34
Reset control ...................................................................................................................................... 35
Interrupt management ........................................................................................................................ 35
Enabling of interrupts at module and NVIC level ............................................................................... 35
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Table of Contents
5.3.2
5.4
Interrupt handler definition (Overriding default handler) .................................................................... 35
Putting it all together .......................................................................................................................... 36
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Introduction
Introduction
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Introduction
1
Introduction
The purpose of this user guide is to provide a broad overview of device initialization. This guide
elaborates upon the various stages of initialization which includes boot-up from a state of reset, CStart and application initialization.
1.1
C-Start (also known as CStart/Startup)
C-Start is essentially a set of activities that must be performed before giving control to the user
application ‘entry point’. A good example of an entry point is the “main” function. Applications
containing operating systems may potentially have an alternative entry point.
1.2
C-Start Packaging
In a few configurations, C-Start functionality is a part of the user application image. In others, C-Start
and user applications are distinct images such as the U-Boot bootloader-for example. Most
embedded systems however have the C-Start functionality combined with the final application.
Figure 1
1.3
C-Start packaging
C-Start tasks
There are two fundamental tasks C-Start is expected to perform. They are:
 Device initialization and any errata workaround implementation
 Program loading
These tasks are elaborated in subsequent chapters.
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Introduction
C-Start tasks
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C-Start tasks
2
C-Start tasks
This chapter describes the various tasks of C-Start. A Cortex-M4 CPU based XMC4 device is used in
the illustrations that follow. Code fragments have been taken from the following files available with the
DAVE distribution:
 startup_XMC4500.s
 System_XMC4500.c
2.1
Figure 2
Device Booting
Booting stages
Figure-1 indicates that after the reset (Either Power-On-Reset or System reset) has been released,
the CPU starts executing the on-chip firmware stored in the BootROM area of memory. The role of
the on-chip firmware is to evaluate the requested chip bootmode and take any necessary actions. As
an example, if the chosen bootmode is ASC BSL mode, the on-chip firmware prepares to download
the user application by first configuring the UART peripheral for IO exchange and subsequently
uploads the user application into PSRAM. The application is received over UART IO lines.
Normal Boot Mode is a commonly deployed boot-mode. On execution, the on-chip firmware reads the
user application vector table, typically placed at the start of the Flash area. It extracts the start
address of the C-Start routines and then cedes control to the reset handler routine.
The vector table on Cortex-M devices is basically a table of function pointers, used to handle CPU
exceptions and device interrupts. The second entry of this table contains the start address of the reset
handler.
Figure 3
Cortex-M vector table
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C-Start tasks
The following code fragment is an extract of the vector table written for the XMC4500 device for the
GNU tool chain.
The Function pointer __Xmc4500_reset_cortex_m is the reset handler and is responsible for device
initialization.
.syntax unified
.section ".Xmc4500.reset"
.globl __Xmc4500_interrupt_vector_cortex_m
.type
__Xmc4500_interrupt_vector_cortex_m, %object
__Xmc4500_interrupt_vector_cortex_m:
.long
__Xmc4500_stack
/* Top of Stack
.long
__Xmc4500_reset_cortex_m
/* Reset Handler
*/
*/
Entry
Entry
Entry
Entry
Entry
*/
*/
*/
*/
*/
NMI_Handler
HardFault_Handler
MemManage_Handler
BusFault_Handler
UsageFault_Handler
/*
/*
/*
/*
/*
NMI Handler
Hard Fault Handler
MPU Fault Handler
Bus Fault Handler
Usage Fault Handler
Note: The on-chip firmware gives control to this reset handler.
Attention: With the exception of the reset handler, all function pointer entries in the vector table
have weak implementations in C-Start. The weakly defined CPU exception and device
interrupt handler routines provide a default implementation. When users provide an
alternative final implementation, these weak definitions are automatically overridden.
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C-Start tasks
2.2
Device initialization
A typical reset handler written for an XMC4 device (specifically, the XMC4500 device) is shown next.
Major functionality is highlighted in bold.
.thumb_func
.globl __Xmc4500_reset_cortex_m
.type
__Xmc4500_reset_cortex_m, %function
__Xmc4500_reset_cortex_m:
.fnstart
/* Insert workarounds here for silicon bugs as necessary */
/* C routines are likely to be called. Setup the stack now */
/* This is already setup by BootROM,hence this step is optional */
LDR SP,=__Xmc4500_stack
/* Clock tree, External memory setup etc may be done here */
LDR
R0, =SystemInit
BLX
R0
/*
SystemInit_DAVE3() is provided by DAVE3 code generation engine. It is
weakly defined here though for a potential override.
*/
LDR
BLX
R0, =SystemInit_DAVE3
R0
/* Perform program loading */
B
__Xmc4500_Program_Loader
.pool
.cantunwind
.fnend
.size
__Xmc4500_reset_cortex_m,.-__Xmc4500_reset_cortex_m
It can be seen from this code fragment that the reset handler invokes a function called SystemInit()
which is responsible for clock tree initialization.
Note: Any user application claiming to conform to the CMSIS standard must invoke the CMSIS routine
SystemInit(), and optionally its extension SystemInit_DAVE3() to perform device initialization.
Users are allowed to insert custom device initialization code in the listing above.
Attention: Device initialization related code must abstain from accessing global variables
because at this stage program loading is still pending.
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C-Start tasks
2.3
Program loading
Once the device initialization code and workarounds for silicon errata are executed, control is given to
the next stage, known as ‘Program Loading’.
The job of a program loader (also known just as a ‘loader’) is to prepare an environment suitable for
user program execution.
A C program typically has the following sections:
 TEXT
 RO-DATA
 DATA
 BSS
 STACK
 HEAP
 USER DEFINED
The job of the program loader is to typically copy TEXT, RO-DATA and DATA from their load address
(Load Memory Area LMA) to run address (Virtual Memory Area VMA).
VMA is the address the various sections of the program are linked to. LMA is the address that they
are stored at. The concepts of LMA and VMA are elaborated in a subsequent chapter.
The start of LMA/VMA and length of a section to be relocated is obtained from the linker script file.
The following is a code snippet of the program loader.
 The program loader is for an application which must eXecute In Place (XIP). DATA is copied from
its LMA in Flash to the VMA in SRAM.
 BSS, which has both LMA and VMA in SRAM, is cleared.
 The resulting effect is that the global data variables are already in an initialized state when control
is eventually ceded to the user application.
.section .Xmc4500.postreset,"x",%progbits
__Xmc4500_Program_Loader:
.fnstart
/* Memories are accessible now*/
/* DATA COPY */
/* R0 =
LDR R0,
LDR R1,
LDR R2,
Start address, R1 = Destination address, R2 = Size */
=eROData
/* Obtained from linker script */
=__Xmc4500_sData /* Obtained from linker script */
=__Xmc4500_Data_Size /* Obtained from linker script */
/* Is there anything to be copied? */
CMP R2,#0
BEQ SKIPCOPY
/* For bytecount less than 4, at least 1 word must be copied */
CMP R2,#4
BCS STARTCOPY
/* Byte count < 4 ; so bump it up */
MOV R2,#4
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C-Start tasks
STARTCOPY:
/*
R2 contains byte count. Change it to word count. It is ensured in the
linker script that the length is always word aligned.
*/
LSR R2,R2,#2 /* Divide by 4 to obtain word count */
/* The proverbial loop from the schooldays */
COPYLOOP:
LDR R3,[R0]
STR R3,[R1]
SUBS R2,#1
BEQ SKIPCOPY
ADD R0,#4
ADD R1,#4
B COPYLOOP
SKIPCOPY:
/* BSS CLEAR */
LDR R0, =__Xmc4500_sBSS
/* Start of BSS obtained from linker script*/
LDR R1, =__Xmc4500_BSS_Size /* BSS size in bytes obtained from linker script */
/* Find out if there are items assigned to BSS */
CMP R1,#0
BEQ SKIPCLEAR
/* At least 1 word must be copied */
CMP R1,#4
BCS STARTCLEAR
/* Byte count < 4 ; so bump it up to a word*/
MOV R1,#4
STARTCLEAR:
LSR R1,R1,#2
/* BSS size in words */
MOV R2,#0
CLEARLOOP:
STR R2,[R0]
SUBS R1,#1
BEQ SKIPCLEAR
ADD R0,#4
B CLEARLOOP
SKIPCLEAR:
/* Remap vector table */
/* This is already setup by BootROM,hence this step is optional */
LDR R0, =__Xmc4500_interrupt_vector_cortex_m
LDR R1, =SCB_VTOR
STR R0,[R1]
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C-Start tasks
2.4
Giving control to the user application entry point
At this stage
 The device initialization is complete with workarounds, and errata optionally executed
 Application data has been relocated from LMA to VMA
The execution environment has been correctly setup and it is time to cede control to the user
application’s entry point. While this is typically the main() function for bare-metal programs, alternative
entry points are possible.
/* Update System Clock */
LDR R0,=SystemCoreClockUpdate
BLX R0
/* C++ : Call global constructors */
LDR R0,=__libc_init_array
BLX R0
/* Reset stack pointer before zipping off to user application, Optional */
LDR SP,=__Xmc4500_stack
MOV R0,#0
MOV R1,#0
/* CEDE CONTROL TO ENTRY POINT OF USER APPLICATION */
LDR PC, =main
The Stack pointer is programmed with the value from the top of the stack, and the program counter is
adjusted to enable the jump to main() routine.
Attention: An alternative application entry point can be programmed into the Program Counter
register.
2.5
Default definition of exception and interrupt handlers
C-Start provides a default definition for each of the CPU exceptions and device interrupt handlers.
The default handlers do no more than implement a self-looping program.
.weak NMI_Handler
.type NMI_Handler, %function
NMI_Handler:
B .
The code listed above is an example of a weakly defined NMI handler routine. Users may in their
application provide an alternative implementation of the NMI Handler. When an alternative
implementation is provided, the linker ignores the weak definition and instead considers the object file
of the alternative definition for linking purposes.
Example: In one of user’s C files:
void NMI_Handler(void){}
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C-Start tasks
Linker scripts
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Linker scripts
3
Linker scripts
3.1
Role of a linker script
This chapter elaborates upon the linker script implementation intended for Infineon’s XMC devices
using the GNU toolchain. Excerpts from linker scripts to be found in the free DAVE tool from Infineon
are used in illustrations that follow.
A linker script defines rules and constraints for the linker. The role of the linker is to assign Load and
Run addresses to application code and data.
Memories on a typical XMC device
Figure 4
3.2
XMC memories and usage
Concept of LMA and VMA
LMA (Load Memory Address) is the address where the program is physically stored.
VMA (Virtual Memory Address) also known as the Run address is the address where the program is
executed from.
Some examples are:
 Program can be stored on flash and executed from SRAM
 Program can be stored and executed from flash
 Some parts of the program can be executed from flash while the rest from SRAM
This concept is pictorially represented here:
Figure 5
LMA and VMA concept
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Linker scripts
3.3
Figure 6
Typical program section assignment
Typical program section placement on a XMC4500 device
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Linker scripts
Figure 7
Typical section placement on a XMC4400 and XMC4200 device
Figure 8
Typical section placement on a XMC1xxx device
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Linker scripts
3.4
Elaboration of GNU linker scripts written for XMC4 devices
OUTPUT_FORMAT("elf32-littlearm")(Indicates that the endianness of the CPU is little endian)
OUTPUT_ARCH(arm) (Indicates that the CPU architecture is ARM)
ENTRY(__Xmc4400_reset_cortex_m)(Indicates that the entry point of the application is
this function)
GROUP(-lxmclibcstubs) (Indicates that a pre-compiled library libxmclibcstubs.a is to be linked in
on a need basis)






MEMORY (Defines various memory regions and their attributes)
{
FLASH_1_cached(RX) : ORIGIN = 0x08000000, LENGTH = 0x80000
FLASH_1_uncached(RX) : ORIGIN = 0x0C000000, LENGTH = 0x80000
PSRAM_1(!RX)
: ORIGIN = 0x1FFFC000, LENGTH = 0x4000
DSRAM_1_system(!RX)
DSRAM_2_comm(!RX)
SRAM_combined(!RX)
: ORIGIN = 0x20000000, LENGTH = 0x8000
: ORIGIN = 0x20008000, LENGTH = 0x8000
: ORIGIN = 0x1FFFC000, LENGTH = 0x14000
}
stack_size = 2048; (Defines the stack size and can be modified as required)
SECTIONS (All output sections are defined and assigned to memory regions above)
{
Output_Section : AT (Load address)
(To be interpreted as “This output section must be linked to Memory_Region but
loaded into Load_Address”)
{
Section_Start_Label = .;
(Used to indicate start address of output section)
*(Input Section1);
(Indicates input sections to be included in this output section)
*(Input Section2);
Section_End_Label = .;
(Used to indicate end address of output section)
} > Memory_Region
}
Without the AT attribute, the LMA and VMA of an output section are the same.
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Linker scripts
3.4.1
Examples
Example1: Positioning of startup code and standard .text
LMA = Uncached flash, VMA = Cached flash
.text : AT (ORIGIN(FLASH_1_uncached))
{
sText = .;
*(.Xmc4500.reset);
*(.Xmc4500.postreset);
*(.XmcStartup);
*(.text .text.* .gnu.linkonce.t.*);
}>FLASH_1_cached
Example2: Positioning of .data
LMA = Uncached flash, , VMA = SRAM
.data ABSOLUTE(ALIGN(16)): AT(eROData)
{
__Xmc4500_sData = .;
* (.data);
* (.data*);
*(*.data);
*(.gnu.linkonce.d*)
__Xmc4500_eData = ALIGN(4);
} > DSRAM_1_system
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Linker scripts
Execution profiles
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Execution profiles
4
Execution profiles
The purpose of this chapter is to touch upon execution profiles and how end users may modify linker
scripts and startup files to suit their own purpose.
Most embedded systems typically support three types of execution profiles
 Execute in Place (XIP) (Code in Non-Volatile memory)
 XIP + Time critical code in volatile memory
 Execution from volatile memory
4.1
Execute in Place (XIP)
This is the default profile available for projects created using the DAVE code generation tool. Code
executes entirely from Flash memory. Variable data is hosted on volatile memory PSRAM.
4.2
XIP + Time critical code in volatile memory
Some time-critical parts of the code have a need to execute from a faster memory (typically SRAM).
XMC4 devices have a Program SRAM block (PSRAM) which serves this purpose. Such code is linked
to the PSRAM address space. XMC1 devices simply call it the SRAM. During program loading, the
program loader copies code from flash to the PSRAM area. There are usually three steps involved in
accomplishing this.
 Creating dedicated sections for time critical code and assigning them a VMA in SRAM
 Assigning time critical code to dedicated sections during compilation time
 Loading time critical code from LMA of aforesaid sections to VMA in PSRAM
4.2.1
Example: Creating a dedicated section for time-critical code in the linker
script
/* Define LMA of dedicated section */
sIRAMCodeLoad = eROData + __Xmc4500_Data_Size;
Attention: In this example, LMA of the dedicated section is after LMA of DATA section
/* Assign special code to this dedicated section */
IRAM_Code : AT (sIRAMCodeLoad)
{
sIRAMCode = ABSOLUTE(.);
* (.IRAMCode); (All time critical code assigned
IRAM_Code which is linked to PSRAM_1)
. = ALIGN(4);
eIRAMCode = ABSOLUTE(.);
} > PSRAM_1
IRAMCodeSize
= eIRAMCode - ORIGIN(PSRAM_1);
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.IRAMCode
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Execution profiles
4.2.2
Example: Assigning time critical code to dedicated sections in source code
void Time_Critical_Routine(void) __attribute__((section(“.IRAMCode”));
4.2.3
Example: Program loader modification for loading time critical code to
SRAM
Attention: BSS clearing code typically follows Data copy code. In this case however, the
PSRAM code loader code follows Data copy and is in turn followed by BSS clear
code.
B DATACOPYLOOP
SKIPDATACOPY: (Note the code specifically introduced for copying the dedicated
section from LMA to VMA)
/* IRAM code copy */
/* R0 = Start address, R1 = Destination address, R2 = Size */
LDR R0, =sIRAMCodeLoad (Start of LMA)
LDR R1, =sIRAMCode (Start of VMA)
LDR R2, =IRAMCodeSize
/* Is there anything to be copied? */
CMP R2,#0
BEQ SKIPIRAMCODECOPY
/* For bytecount less than 4, at least 1 word must be copied */
CMP R2,#4
BCS STARTIRAMCODECOPY
/* Byte count < 4 ; so bump it up */
MOV R2,#4
STARTIRAMCODECOPY:
/*
R2 contains byte count. Change it to word count. It is ensured in the
linker script that the length is always word aligned.
*/
LSR R2,R2,#2 /* Divide by 4 to obtain word count */
/* The proverbial loop from the schooldays */
IRAMCODECOPYLOOP:
LDR R3,[R0]
STR R3,[R1]
SUBS R2,#1
BEQ SKIPIRAMCODECOPY
ADD R0,#4
ADD R1,#4
B IRAMCODECOPYLOOP
SKIPIRAMCODECOPY:
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Execution profiles
/* BSS CLEAR */
4.3
Complete code execution from SRAM
There are cases where the whole of the TEXT section is to be executed from SRAM. This is
accomplished by linking the TEXT section to PSRAM addresses. Optionally, any constant data
needed by the TEXT can also be linked to the PSRAM address space.
The linker script and the program loader code change. User applications do not change.
4.3.1
Example: Linker script modification
/* TEXT section */
Startup : AT(ORIGIN(FLASH_1_uncached))
{
StartText = ABSOLUTE(.);
*(.Xmc4500.reset);
*(.Xmc4500.postreset);
*(.XmcStartup);
. = ALIGN(4);
eStartup = ABSOLUTE(.);
} > FLASH_1_cached
Note, it is only the vector table and startup code that are linked to flash
address space. Standard .text section is separated out and linked to PSRAM section
below. LMA of this section is in flash while the VMA is in PSRAM.
StartupSize = eStartup - StartText;
sUserTextLoad = ORIGIN(FLASH_1_uncached)+ StartupSize;
.text ABSOLUTE(ORIGIN(PSRAM_1)): AT(sUserTextLoad)
{
sUserTextRun = ABSOLUTE(.);
*(.text .text.* .gnu.linkonce.t.*);
. = ALIGN(4);
eUserTextRun = ABSOLUTE(.);
} > PSRAM_1
UserTextSize = eUserTextRun - sUserTextRun;
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Execution profiles
4.3.2
Example: Program loader modification
/* Copy
/* R0 =
LDR R0,
LDR R1,
LDR R2,
the TEXT from flash to PSRAM */
Start address, R1 = Destination address, R2 = Size */
=sUserTextLoad
=sUserTextRun
=UserTextSize
STARTPROGCOPY:
/*
R2 contains byte count. Change it to word count. It is ensured in the
linker script that the length is always word aligned.
*/
LSR R2,R2,#2 /* Divide by 4 to obtain word count */
/* The proverbial loop from the schooldays */
PROGCOPYLOOP:
LDR R3,[R0]
STR R3,[R1]
SUBS R2,#1
BEQ SKIPPROGCOPY
ADD R0,#4
ADD R1,#4
B PROGCOPYLOOP
SKIPPROGCOPY:
/* Copy RODATA from flash to PSRAM */
/* R0 = Start address, R1 = Destination address, R2 = Size */
LDR R0, =sRODataLoad
LDR R1, =sRODataRun
LDR R2, =RODataSize
/* Is there anything to be copied? */
CMP R2,#0
BEQ SKIPRODATACOPY
/* For bytecount less than 4, at least 1 word must be copied */
CMP R2,#4
BCS STARTRODATACOPY
/* Byte count < 4 ; so bump it up */
MOV R2,#4
STARTRODATACOPY:
/*
R2 contains byte count. Change it to word count. It is ensured in the
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linker script that the length is always word aligned.
*/
LSR R2,R2,#2 /* Divide by 4 to obtain word count */
/* The proverbial loop from the schooldays */
RODATACOPYLOOP:
LDR R3,[R0]
STR R3,[R1]
SUBS R2,#1
BEQ SKIPRODATACOPY
ADD R0,#4
ADD R1,#4
B RODATACOPYLOOP
SKIPRODATACOPY:
/* Copy DATA from flash to DSRAM1 */
/* R0 = Start address, R1 = Destination address, R2 = Size */
LDR R0, =DataLoad
LDR R1, =__Xmc4500_sData
LDR R2, =__Xmc4500_Data_Size
/* Is there anything to be copied? */
CMP R2,#0
BEQ SKIPDATACOPY
/* For bytecount less than 4, at least 1 word must be copied */
CMP R2,#4
BCS STARTDATACOPY
/* Byte count < 4 ; so bump it up */
MOV R2,#4
STARTDATACOPY:
Attention: TEXT, RO-DATA and DATA are copied to the VMA area from their LMA area by the
program loader.
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Device initialization hints
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Hints on device initialization
5
Hints on device initialization
5.1
Timing of device initialization
The purpose of this chapter is to elaborate upon device initialization topics.
Attention: It must be expressly stated that the scope of device initialization is entirely
dependent on the end user. There are no fixed rules on what constitutes device
initialization.
Some examples that constitute device initialization are:
 Clock tree configuration
 Reset configuration
 Peripheral enabling and initialization
 Interrupt configuration
There are no set rules on the timing of device initialization. It can be performed at any time. In some
cases, this is done before program loading, sometimes after program loading and before application
entry, and many times this is entirely handled by the user application.
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Hints on device initialization
5.2
Clock and reset configuration
5.2.1
System clock configuration algorithm
Figure 9
System Clock selection algorithm




The System clock can be sourced by either the backup clock or by the PLL.
The PLL can be operated in either a prescalar mode or the normal mode.
Input clock to PLL can either be the backup clock or the external clock.
The high precision oscillator can be turned off if the backup clock is being used as a clock source
(either as an input to PLL or directly used as the system clock).
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Hints on device initialization

The VCO can be powered down if the system clock is to be derived from either the backup clock
or the high precision oscillator clock (PLL prescalar mode).
5.2.2
Using the backup clock as system clock (fSYS = fOFI)
/* Set fSYS to fOFI */
SCU_CLOCK->SYSCLKCR = 0U;
5.2.3
Using the oscillator clock as system clock (fSYS = fPLL)
/* Setup oscillator and connect crystal/clock to it - See next hint*/
/* Get PLL out of power saving mode */
SCU_PLL->PLLCON0 &= ~(1U << 16);
/* Select oscillator output as input to P and K1 divider */
SCU->PLLCON2 = 0U; /* PINSEL = K1INSEL = fOHP */
/* Configure K1 divider */
SCU_PLL->PLLCON1 = 0U; /* No division */
/* Bypass the VCO – fPLL = fK1*/
SCU_PLL->PLLCON1 |= 1U; /* Bypass the VCO */
/* Power the VCO down to save power */
SCU_PLL->PLLCON1 |= 1U << 1U;
/* Set fSYS to fPLL. fSYS = fPLL = fK1 */
SCU_CLOCK->SYSCLKCR = 1U << 16U;
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Hints on device initialization
5.2.4
Downscaling the System clock (fSYS)
/* Program SYSDIV – Divide source of system clock by 8 (Example)*/
SCU_CLOCK->SYSCLKCR |= 7U;
5.2.5
Setting up the oscillator
/* Configure oscillator mode – E.g 20MHZ Crystal connected to oscillator */
SCU_OSC->OSCHPCTRL = ~(0x3U << 4);
/* Configure OSCVAL to generate correct osc watchdog reference clock of 2.5Mhz*/
SCU_OSC->OSCHPCTRL |= 7U << 16;
/* Get PLL out of power saving mode */
SCU_PLL->PLLCON0 &= ~(1U << 16);
/* Restart oscillator watchdog */
SCU_PLL->PLLCON0 |= 1U << 17;
/* Wait until oscillator output is deemed usable */
while (3 != ( ( (SCU_PLL->PLLSTAT)& (3U << 7)) >> 7) );
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Hints on device initialization
5.2.6
VCO output configuration and PLL lock
/* Example, fRef = 12Mhz, VCO output to 480Mhz, */
/* Get PLL out of power saving mode */
SCU_PLL->PLLCON0 &= ~(1U << 16);
/* Setup either backup clock/osc output as system clock – See previous hints */
/* So that fSYS=fOFI or fSYS=fPLL where fPLL=fK1 */
/* Disable PLL input */
SCU_PLL->PLLCON0 |= (1U << 4);
/* Take VCO out of power down mode */
SCU_PLL->PLLCON0 &= ~(1U << 1);
/* Define trim range for normal operation */
SCU_PLL->PLLCON0 &= ~(1U << 2);
/* Temporarily disable disconnection of source upon loss of PLL lock */
SCU_PLL -> PLLCON0 |= 1U << 6;
/* Program
SCU_PLL ->
SCU_PLL ->
SCU_PLL ->
N=40, P=1,
PLLCON1 |=
PLLCON1 &=
PLLCON1 |=
K2=1 dividers – Set PDIV, K2DIV and NDIV */
1U << 24; /* P = PDIV + 1 = 2 */
~(0x7F << 16); /* K2 = K2DIV + 1 = 1 */
(39U << 8); /* N = NDIV + 1 = 40 */
/* Enable PLL input */
SCU_PLL->PLLCON0 &= ~(1U << 4);
/* Re-Start VCO lock detection – Set RESLD */
SCU_PLL -> PLLCON0 |= 1U << 18;
/* Wait until VCO output locks to input frequency */
while(!(((SCU_PLL->PLLSTAT) &(1U << 2))>>2));
/* Re-enable disconnection of source upon loss of PLL lock */
SCU_PLL -> PLLCON0 &= ~(1U << 6);
/* Enable NORMAL mode of operation – fPLL = fK2 = fVCO / K2*/
SCU_PLL->PLLCON0 &= ~ (1U);
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Hints on device initialization
5.2.7
Target frequency ramp-up
/* Hint to ramp up fPLL to 120Mhz */
/* Example - Entry conditions
PLL = Normal mode
fSYS = fPLL = fK2
VCO output = 480Mhz, Locked to input
N and P dividers programmed, K2 set to 20
fK2 = 24Mhz
*/
/* Rampup fK2 to 60Mhz by changing K2 to 8 */
/* Wait for 50us */
/* Rampup fK2 to 96Mhz by changing K2 to 5 */
/* Wait for 50us */
/* Rampup fK2 to 120Mhz by changing K2 to 4 */
/* Wait for 50us */
5.2.8
CPU clock and peripheral bus clock
The CPU clock is sourced by fSYS. It can be halved if desired. Otherwise, fCPU is the same as fSYS.
SCU_CLOCK->CPUCLKCR = 1U; /* fCPU = fSYS/2 */
The Interface clock for peripherals is derived from fCPU. Usually, fPERIPH is the same as fCPU, but
can be halved if required.
SCU_CLOCK ->PBCLKCR = 1U; /* fPERIPH = fCPU/2 */
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Hints on device initialization
5.2.9
Peripheral clock configuration
Most peripheral clocks derived out of fSYS can be downscaled by using dividers. There are dedicated
clock control registers available. As an example, CCU clock division can be controlled by
programming CCUDIV bit.
SCU_CLK->CCUCLKCR = 1U; /* fCCU = fSYS / 2 */
5.2.10
Peripheral clock control
Peripheral clocks can be individually controlled using CLKSET and CLKCLR registers.
The status of a peripheral clock can be found by reading the CLKSTAT register.
SCU_CLOCK->CLKSET |= (1U << 5U); /* To enable WDG clock */
SCU_CLOCK ->CLKCLR &= ~(1U << 5U); /* To disable WDG clock */
5.2.11
Clock gating during sleep modes
The behavior of various peripheral clocks can be controlled on entry to sleep modes. Registers
SLEEPCR and DEEPSLEEPCR need to be programmed for this.
For example, in order to turn off the CCU clock during sleep and deep sleep modes, use:
SCU_CLK->SLEEPCR |= (1U << 20U);
SCU_CLK->DEEPSLEEPCR |= (1U << 20U);
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Hints on device initialization
5.2.12
Reset control
All peripherals are kept in a state of reset which must be released before they are programmed for the
required functionality. Conversely, an active peripheral can be taken into a state of reset.
SCU_RESET -> PRCLR0 |= (1U << 11U); /* Release the reset on USIC0 */
SCU_RESET -> PRSET0 |= (1U << 0U); /* Reset VADC */
The module reset state can be found by reading the PRSTAT register.
5.3
Interrupt management
Modules generate events which potentially can lead to interrupts. To accomplish this, Interrupts must
be enabled at:
 Module level
 NVIC level
 CPU level
Interrupt handlers must be defined which override the default definitions from C-Start.
Attention: Interrupts on XMC devices are known as service requests.
When an interrupt occurs, the CPU stops executing the main program and instead executes the
interrupt handler routine. Once an interrupt has been handled, control returns back to the main
program.
The code snippet that follows shows how LEDTS interrupts may be handled on a XMC4500 device.
LEDTS service request is connected to Node-102 of NVIC.
5.3.1
Enabling of interrupts at module and NVIC level
LEDTS0->GLOBCTL |= 1U << 13; /* Enable time slice interrupt */
NVIC_SetPriority(102, 60); /* Assign a priority of 60 to Node-102 */
NVIC_EnableIRQ(102); /* Enable IRQ-102 */
5.3.2
Interrupt handler definition (Overriding default handler)
C-Start defines a default interrupt handler for all of the CPU exceptions and device interrupts. For the
interrupt enabled above, user applications may define a final handler to meet their particular needs.
void LEDTS0_0_IRQHandler(void){} /* overrides the default interrupt handler */
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5.4
Putting it all together
The following example pieces all of the information together.
int main(void)
{
/* Select fOFI as system clock */
SCU_CLOCK -> SYSCLKCR &= ~(1U << 16U);
/* Release the LEDTS reset */
SCU_RESET-> PRCLR1 |= (1U << 3);
/* Do not proceed until and unless the reset is confirmed as released */
while(1){
unsigned Status = SCU_RESET->PRSTAT1;
Status = (Status>>3) & 1;
if(!Status) break;
}
/* LEDTS configuration */
LEDTS0->GLOBCTL = 1U << 0; /* Enable Touchsense functionality */
LEDTS0->GLOBCTL |= 1U << 1; /* Enable LED functionality */
LEDTS0 ->GLOBCTL|= 1U << 13; /* Enable time slice interrupt */
NVIC_SetPriority(102, 60); /* Assign a priority of 60 to Node-102 */
NVIC_EnableIRQ(102); /* Enable IRQ-102 */
/* Other LEDTS configuration */
/* Finally */
while(1);/* All processing is now handled in the ISR */
}
void LEDTS0_0_IRQHandler(void)
{
/* Confirm interrupt is genuine */
/* Handle it – user application*/
}
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w w w . i n f i n e o n . c o m
Published by Infineon Technologies AG
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