TI_C6000_Chapter11

Chapter 11, Slide 8
Dr. Naim Dahnoun, Bristol University, (c) Texas Instruments 2004
Passing Arguments between C and Assembly
Solution: Both the C code and assembly code are C code responsible for automatically saves these saving some registers registers if they need to use them.
Dr. Naim Dahnoun, Bristol University, (c) Texas Instruments 2004
Passing Arguments between C and Assembly
Problem: The C code will use some or all of the registers. The assembly code may also require the use of some or all registers. If nothing is done then on return to the C code some of the values may have been destroyed by the assembly code.
arg1/r_val arg1/r_val arg3 arg5 arg7 arg9
ret addr arg2 arg4 arg6 arg8 arg10
Chapter 11, Slide 6
Dr. Naim Dahnoun, Bristol University, (c) Texas Instruments 2004
Programming requirements when interfacing code.
Chapter 11, Slide 2
Dr. Naim Dahnoun, Bristol University, (c) Texas Instruments 2004
Introduction
This chapter shows how to interface C and assembly and how to use intrinsics. As a general rule the code written in C is used for initialisation and for non-critical (in terms of nonspeed or size) code. Critical code (in terms of speed/size) can be written in assembly or linear assembly. There are three different ways to interface C and assembly code: (1) C code call to the assembly function. (2) An interrupt can call an assembly function. (3) Call an assembly instruction using intrinsics.
\Code\Chapter 14 - Finite Impulse Response Filters Code\ \Code\Chapter 16 - Adaptive Filters Code\
Setup code written in C and interfaced with critical code written in linear assembly can be found in the following chapters:
Assembly code must save these registers responsibility of the programmer
Chapter 11, Slide 9
A 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
B
Dr. Naim Dahnoun, Bristol University, (c) Texas Instruments 2004
Chapter 11, Slide 4 Dr. Naim Dahnoun, Bristol University, (c) Texas Instruments 2004
Calling Assembly from C
main_c.c
int asm_Function (short, short); short x = 0x4000, y = 0x2000; int z; void main (void) { z = asm_Function (x, y); }
Chapter 11, Slide 3 Dr. Naim Dahnoun, Bristol University, (c) Texas Instruments 2004
Calling Assembly from C
main () { y = asmFunction (a, b); }
_asmFunction b b3
Interfacing C and Assembly Examples
Setup code written in C and interfaced with critical code written in assembly can be found in the following chapters:
\Code\Chapter 15 - Infinite Impulse Response Filters Code\ \Code\Chapter 17 - Goertzel Algorithm Code\
Chapter 11, Slide 10
Dr. Naim Dahnoun, Bristol University, (c) Texas Instruments 2004
Chapter 11 Interfacing C and Assembly Code - End -
Use “_” underscore in assembly for all variables or functions declared in C. Labels also need to be global.
asm_Function.asm
.global _asm_Function
asm_Function.c
Passing Arguments between C and Assembly
A B 4 5 6 7 8
0x2000
Before assembly call.
0x4000
After return from assembly call.
0x8000
4 5 6 7 8
0x2000
Байду номын сангаас
Chapter 11, Slide 7
The C and assembly functions share the same resources (e.g. registers). The C and assembly functions may exchange data. Therefore code interfacing requires a means of handinghanding-off data and control info and some rules of handling shared registers.
Passing Arguments between C and Assembly
A B 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
The following registers are used to pass and return variables when calling an assembly routine from C.
int asm_Function (short a, short b) { int y; y = (a * b) << 1; return y;
}
Chapter 11, Slide 5
Dr. Naim Dahnoun, Bristol University, (c) Texas Instruments 2004
Chapter 11 Interfacing C and Assembly Code
Learning Objectives
Different methods exist for interfacing C and assembly code:
Calling assembly from C. Interrupt calling assembly routine. Intrinsics.