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56800E
Coding
Guidlines
for
Small Data Memory
Model and
56F8300
Large Data Memory
Model
Hybrid Controller
CG56800E
Rev. 0, 06/2004
MOTOROLA.COM/SEMICONDUCTORS
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Contents
About This Document
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Audience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
Suggested Reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi
Definitions, Acronyms, and Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
1
Introduction
1.1
Switching Between Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1
2
Coding Guidelines
2.1
2.2
2.3
2.4
2.5
Type Casting Pointers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1
Conversion of 56800 Instructions to 56800E Instructions . . . . . . . . . . . . . . . . . . . 1-1
LoadRx, StoreRx, and TestRx Macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1
Push and Pop Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2
Structure Offsets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3
Table of Contents
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ii
56800E Coding Guidelines for SDM and LDM
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List of Examples
2-1
2-2
2-3
2-4
2-5
Use Macros to Convert DSP56800 or DSP56800E Assembly Code . . .
Converting 56800 Assembly Code Using Push and Pop #1. . . . . . . . . .
Converting 56800 Assembly Code using Push and Pop #2 . . . . . . . . . .
Convert C structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Convert Assembly Code Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1-2
1-2
1-3
1-3
1-4
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Code Example
Code Example
Code Example
Code Example
Code Example
List of Examples
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iv
56800E Coding Guidelines for SDM and LDM
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About This Document
This manual describes some coding guidelines in order to generate valide code for both a Small Data
Memory model (SDM) and a Large Data Memory model (LDM) target for a 56800E application.
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Audience
This document targets software developers who have implemented software applications with 56800
devices and are converting to the 56800E family of devices.
Suggested Reading
We recommend that you have a copy of the following references:
•
•
•
•
DSP56800 to DSP56800E Porting Guide, DSP56800ERG/D
DSP56800 Family Manual, DSP56800FM/AD
DSP56800E Reference Manual, DSP56800ERM/AD
Inside CodeWarrior: Core Tools, Metrowerks Corp.
Preface
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Conventions
This document uses the following notational conventions:
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Typeface, Symbol
or Term
Meaning
Examples
Courier
Monospaced Type
Code examples
//Process command for line flash
Italic
Directory names,
project names,
calls,
functions,
statements,
procedures,
routines,
arguments,
file names,
applications,
variables,
directives,
code snippets
in text
...and contains these core directories:
applications contains applications software...
Bold
Reference sources,
paths,
emphasis
...refer to the Targeting DSP56F80x Platform
manual....
...see: C:\Program Files\Motorola\help\tutorials
Blue Text
Linkable on-line
...refer to Chapter 7, License....
Number
Any number is considered a
positive value, unless preceded by a minus symbol to
signify a negative value
3V
-10
DES-1
ALL CAPITAL
LETTERS
# defines/
defined constants
# define INCLUDE_STACK_CHECK
Brackets [...]
Function keys
...by pressing function key [F7]
Quotation
marks, “...”
Returned messages
...the message, “Test Passed” is displayed....
...CodeWarrior project, 3des.mcp is...
...the pConfig argument....
...defined in the C header file, aec.h....
...if unsuccessful for any reason, it will return
“NULL”...
vi
56800E Coding Guidelines for SDM and LDM
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Definitions, Acronyms, and Abbreviations
The following list defines the acronyms and abbreviations used in this document. As this template
develops, this list will be generated from the document. As we develop more group resources, these
acronyms will be easily defined from a common acronym dictionary. Please note that while the acronyms
are in solid caps, terms in the definition should be initial capped ONLY IF they are trademarked names or
proper nouns.
DSP
Digital Signal Processor or Digital Signal Processing
LDM
Large Data Memory
SDM
Small Data Memory
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References
The following sources were referenced to produce this book:
1. DSP56800 to DSP56800E Porting Guide, DSP56800ERG/D
2. DSP56800 Family Manual, DSP56800FM/AD
3. DSP56800E Reference Manual, DSP56800ERM/AD
4. Inside CodeWarrior: Core Tools, Metrowerks Corp.
Preface
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vii
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viii
56800E Coding Guidelines for SDM and LDM
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1
Introduction
1.1 Switching Between Models
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A Small Data Memory model (SDM) and a Large Data Memory model (LDM) are available for
the 56800E family of hybrid controllers. The SDM has a maximum address size of 16 bits for
both data and program addresses. This allows for smaller, compact code size, since an address can
be stored in one 16-bit word. The LDM has a maximum address size of 19 bits for program
addresses and 21 bits for data addresses. This allows an application to use more memory, but it
requires two 16-bit words of memory to store each address.
In order to switch between the different models during development, specific coding practices
should be followed to make this as transparent as possible. The remainder of this document
describes these practices.
2
Coding Guidelines
This section explains how the user’s source code should be developed in order to generate code
for both the SDM and LDM.
2.1 Type Casting Pointers
When developing software for the SDM, do not type cast pointers to be 16 bits (i.e., unsigned int).
This will work for the SDM, but if you switch to the LDM, it may not work, because your pointer
size may be greater than 16 bits.
2.2 Conversion of 56800 Instructions to 56800E Instructions
When the 56800E was developed, one requirement was the ability to use all of the 56800
instructions to easily upgrade from the 56800 to the 56800E. This approach works fine for the
SDM; however, since the 56800 instructions are for a 16-bit DSP with 16-bit pointers, this
approach is no longer valid when using the LDM.
When using the LDM, the “allow legacy instructions” Language Settings: M56800E Assembler
option must be turned off and the user must convert all 56800 instructions to 56800E instructions.
Please see the DSP56800 to DSP56800E Porting Guide to learn more.
2.3 LoadRx, StoreRx, and TestRx Macros
When loading, storing, or testing pointers in Assembly, you must specify if it is a word or a long.
For the SDM, pointers are a word and for the LDM, pointers are a long.
Depending on the model, defined macros in portasm.h ease switching from SDM to LDM and
vice versa. These assembly macros (LoadRx, StoreRx, and TestRx) are defined based on which
model is used, so they load, store, and test the correct size of the pointer.
56800E Coding Guidelines for SDM and LDM
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Code Example 2-1. Use Macros to Convert DSP56800 or DSP56800E Assembly Code
56800 Assembly code:
move
move
tstw
X:(R2+Offset_pCircBuffer),R0 ; where pCircBuffer contains a pointer
R0,X:(R2+Offset_pCircBuffer)
X:(R2+Offset_pCircBuffer)
or 56800E Assembly code (SDM):
moveu.w X:(R2+Offset_pCircBuffer),R0 ; where pCircBuffer contains a pointer
move.w R0,X:(R2+Offset_pCircBuffer)
tst.w X:(R2+Offset_pCircBuffer)
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or 56800E Assembly code (LDM):
move.l X:(R2+Offset_pCircBuffer),R0 ; where pCircBuffer contains a pointer
move.l R0,X:(R2+Offset_pCircBuffer)
tst.l X:(R2+Offset_pCircBuffer)
can be converted to:
LoadRx X:(R2+Offset_pCircBuffer),R0 ; where pCircBuffer contains a pointer
StoreRx R0,X:(R2+Offset_pCircBuffer)
TestRx X:(R2+Offset_pCircBuffer)
2.4 Push and Pop Instructions
The 56800 has instructions for push and pop that save and restore 16-bit address registers. The
push and pop instructions should not be used for the 56800E, since these instructions temporarily
even the stack. This could cause alignment access problems for long data types, since long data
types must be on odd addresses.
If 56800 Assembly code is being ported to the 56800E and it contains push or pop instructions,
this code should be rewritten so it does not use these instructions.
Code Example 2-2. Converting 56800 Assembly Code Using Push and Pop #1
56800 Assembly code:
push R2
...
pop R2
can be converted to:
adda #2,sp
move.l R2,x:(sp)
...
move.l x:(sp)-,R2
2-2
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Code Example 2-3. Converting 56800 Assembly Code using Push and Pop #2
DSP56800 Assembly code:
push Y0
push Y1
...
pop Y1
pop Y0
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can be converted to:
adda #2,sp
move.w Y0,x:(sp)
move.w Y1,x:(sp-1)
...
move.w x:(sp-1),Y1
move.w x:(sp),Y0
suba #2,sp
2.5 Structure Offsets
If your assembly code accesses elements of a structure defined in C, offsets to the elements of the
structure must be defined in Assembly. In portasm.h, a PTR_SIZE macro has been created that
defines the size of a pointer (1 for SDM and 2 for LDM). To seamlessly switch from SDM to
LDM and vice versa, assembly code that defines offsets to these elements should be relative to the
previous element and PTR_SIZE should be used when specifying the size of a pointer.
Also, structure elements that are longs should be the first elements in the structure, because
CodeWarrior requires that long values start on an odd address. Structure elements that are pointers
should follow because they will be longs for LDM. By having all of the longs and pointers first,
the start of the structure will be on an odd address and there will be no gaps in the structure. If
longs or pointers were placed in the middle of the structure, then gaps would be inserted to
guarantee an odd address. Because Assembly code is written to assume no gaps, this would cause
a problem.
Code Example 2-4. Convert C structure
If C structure is defined as follows:
struct C_Structure {
bool bStatus;
int * pCircBuffer;
int
Size;
UWord32 LongWord;
};
56800E Coding Guidelines for SDM and LDM
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then you can change the C structure to the following:
struct C_Structure {
UWord32 LongWord;
int * pCircBuffer;
bool bStatus;
int
Size;
};
Code Example 2-5. Convert Assembly Code Structure
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If Assembly code defines these offsets to each element as follows:
Offset_bStatus
Offset_pCircBuffer
Offset_size
Offset_LongWord
equ
equ
equ
equ
0
1
2
3
then you can change the Assembly code to the following:
Offset_LongWord
Offset_pCircBuffer
Offset_bStatus
Offset_size
2-4
equ
equ
equ
equ
0
Offset_LongWord+2
Offset_pCircBuffer+PTR_SIZE
Offset_bStatus+1
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Index
D
DSP vii
Digital Signal Processor vii
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L
LDM vii
Large Data Memory Model vii
LoadRx 1-1
long 1-1
longs 1-3
M
M56800E Assembler 1-1
P
pointers 1-3
pop 1-2
portasm.h 1-1, 1-3
PTR_SIZE macro 1-3
push 1-2
S
SDM vii
Small Data Memory Model vii
StoreRx 1-1
T
TestRx 1-1
W
word 1-1
Index
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CG56800E
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