OK6410裸机学习之汇编调用C函数传参数

start.S汇编源码：

.globl _start

_start:

// 硬件相关的设置 

    // Peri port setup 

    ldr r0, =0x70000000

    orr r0, r0, #0x13

    mcr p15,0,r0,c15,c2,4       @ 256M(0x70000000-0x7fffffff)

// 关看门狗 

    // 往WTCON(0x7E004000)写0    

    ldr r0, =0x7E004000

    mov r1, #0

    str r1, [r0]

// 设置栈 

    ldr sp, =6*1024

    // int xxxxx(int start, int end, int a, int b, int c, int d) 

    mov r0, #0   // start 

    mov r1, #8   // end 

    mov r2, #0   // a 

    mov r3, #0   // b 

    // c, d 存在栈里 ,C函数的参数超过4个以后超过的部分存在栈里

    // 栈是向下增长的，数据入栈时SP指针先减再存入数据

    // 把sp栈顶的位置先减8，对于32位的单片机一个寄存器32位4个字节，减8可以存两个寄存器的值

    ldr sp, =6*1024-8;  

    mov r4, #0

    str r4, [sp]              // c 

    mov r4, #1

    str r4, [sp, #4]        // d ，把参数d的值r4存在sp+4的位置

    // 到此sp-8预留的空间已经存入了c、d两个参数

    bl xxxxx

halt:

    b halt    

=====================================================================

led.c源码:

void delay(int a, int b, int c, int d, int e, int f, int g, int h)

{

    volatile int i = a+b+c+d+e+f+g+h;

    while (i--);

}

int xxxxx(int start, int end, int a, int b, int c, int d)

{

    int i = start + a + b + c + d;

    volatile unsigned long *gpmcon = (volatile unsigned long *)0x7F008820;

    volatile unsigned long *gpmdat = (volatile unsigned long *)0x7F008824;

    // gpm0,1,2,3设为输出引脚 

    *gpmcon = 0x1111;

    while (1)

    {

        *gpmdat = i;

        i++;

        if (i == end)

            i = start;

        delay(0, 1, 2, 3, 4, 5, 6, 0x10000);

    }

    return 0;

}

=====================================================================

Makefile:

led.bin: start.o led.o

    arm-linux-ld -Ttext 0 -o led.elf start.o led.o

    arm-linux-objcopy -O binary led.elf led.bin

    arm-linux-objdump -D led.elf > led.dis

start.o : start.S

    arm-linux-gcc -o start.o start.S -c -O2

led.o : led.c

    arm-linux-gcc -o led.o led.c -c -O2

clean:

    rm *.o led.elf led.bin led.dis