This paper mainly describes the mixed programming of C and assembly language. Assembly language refers to arm assembly language. This paper is used to help understand the assembler in ARM embedded system and how to mix C language with assembler.
Main software: keiL μ Vision5
1, Introduction to ARM assembly language
What is assembly language? Assembly language is any low-level language suitable for electronic computers, microprocessors or other programmable devices. Although it is called "low-level language", it does not mean that assembly language is really "low-level". Specific assembly language and specific machine language instruction set are one-to-one corresponding, and can not be transplanted directly between different platforms. Assembly language mainly includes transmission instruction, logic operation, shift instruction, bit operation, control transfer, string operation, input and output and so on.
2, C language calls assembly language
1. No parameter call
Creating project files in Keil has been introduced in my previous blog. I won't introduce it too much here.
First create the project file, and then add CORE and startup
Then right click the Source Group in the left project file and select Add New Item
Add Fun.s and main.c files successively
Func.s
AREA My_Function,CODE,READONLY ;There must be something in this line except My_Function You can choose your own name. All the others are templates EXPORT Init_1 ;With in C Defined in the file Init_1 Function Association ;The declaration and use of variables in high-level languages are actually the use of registers, so we only need to use registers directly Init_1 MOV R1,#0 ; Let R1 register be i MOV R2,#0 ; Let R2 register be j LOOP ;Written on the far left is the segment name of the program segment, which is used when executing the jump program CMP R1,#ten ; Compare the sizes of R1 and 10 BHS LOOP_END ;If R1 Greater than or equal to 10, jump to LOOP_END On the contrary, ignore the statement and directly execute the following statement ADD R2,#1 ;j++ ADD R1,#1 ;i++ B LOOP ;After executing a cycle, unconditionally enter the cycle judgment again, that is, jump to LOOP paragraph LOOP END NOP END ;Write after the required space END，Otherwise, it will be regarded as the segment name, indicating the end of the program
main.c
#include<stdio.h>
extern void Init_1(void);
int main()
{
Init_1();
return 0;
}
Note: you need to check software debugging and then modify parameters. The chip selected at the beginning is stmf103c8, so - pSTM32F103C8 is filled in the Parameter here
Set breakpoint
You can observe the program operation through register changes
2. Parameter call
Simply modify the code
Func.s
AREA My_Function,CODE,READONLY ;There must be something in this line except My_Function You can choose your own name. All the others are templates EXPORT Init_1 ;With in C Defined in the file Init_1 Function Association ;The declaration and use of variables in high-level languages are actually the use of registers, so we only need to use registers directly Init_1 ADD R0,#one hundred ; Add the passed in value + 100 MOV PC,LR ;return R0 LOOP ;Written on the far left is the segment name of the program segment, which is used when executing the jump program CMP R1,#ten ; Compare the sizes of R1 and 10 BHS LOOP_END ;If R1 Greater than or equal to 10, jump to LOOP_END On the contrary, ignore the statement and directly execute the following statement ADD R2,#1 ;j++ ADD R1,#1 ;i++ B LOOP ;After executing a cycle, unconditionally enter the cycle judgment again, that is, jump to LOOP paragraph LOOP_END NOP END ;Write after the required space END，Otherwise, it will be regarded as the segment name, indicating the end of the program
main.c
#include<stdio.h>
extern int Init_1(int x);
int main()
{
printf("%d",Init_1(420));
return 0;
}
The debugger observes register changes
At this time, the value of R1 register is 0x208, i.e. 520, and the call is successful.
3, Assembly language calls C language
Modify code
Func.s
AREA My_Function,CODE,READONLY ;There must be something in this line except My_Function You can choose your own name. All the others are templates EXPORT Init_1 ;With in C Defined in the file Init_1 Function Association IMPORT return1 ;statement return1 Is an external reference ;The declaration and use of variables in high-level languages are actually the use of registers, so we only need to use registers directly Init_1 ADD R0,#one hundred ; Add the passed in value + 100 MOV PC,LR ;return R0 LOOP ;Written on the far left is the segment name of the program segment, which is used when executing the jump program CMP R1,#ten ; Compare the sizes of R1 and 10 BHS LOOP_END ;If R1 Greater than or equal to 10, jump to LOOP_END On the contrary, ignore the statement and directly execute the following statement ADD R2,#1 ;j++ ADD R1,#1 ;i++ B LOOP ;After executing a cycle, unconditionally enter the cycle judgment again, that is, jump to LOOP paragraph LOOP_END NOP END ;Write after the required space END，Otherwise, it will be regarded as the segment name, indicating the end of the program
main.c
#include<stdio.h>
extern int Init_1(int x);
int return1(void);
int main()
{
int x = Init_1(420);
printf("%d",x);
return 0;
}
int return1(void)
{
return 1;
}
Compile and debug
You can see that the value of R0 changes to 1, which shows that the C function is successfully called.
4, Summary
This experiment needs to learn the relevant knowledge of C language and assembly language, as well as how to call the parameters of C language and assembly language, so as to lay a certain foundation for embedded in the future.
5, References
Assembly language (machine oriented programming language)_ Baidu Encyclopedia (baidu.com)