c程序调用汇编函数

c程序调用汇编函数程序实例：按键控制led灯/*************************   main.c**************************/static int (*printf)(const char *format,...) = (int (*)(const char *format,...))0xc3e11ad0void _start(){  printf("%s , %s \n", __FUNCTION__, __LINE__);  led_init();  key_init();  while(1)  {led_on(key_stat());  }  }/*************************   led_key.S**************************///转载请注明原文地址:http://blog.csdn.net/oyhb_1992/article/details/77822816#define GPM4CON 0X110002E0#define GPM4DAT 0X110002E4#define GPX3CON 0X11000C60#define GPX3DAT 0X11000c64.global  led_initled_init: //GPM4_0~3设为输出         //GPM4CON = (GPM4CON & ~0XFFFF) | 0X1111led_init: ldr r0 , =GPM4CON          ldr r1 , [r0]         bic r1 , #0xff         bic r1 , #0xff00 //0xffff 0x1111都是非法立即数，两种方法，拆开立即数或用伪指令         ldr r2 , #0x1111         orr r1 , r2         str r1 , [r0]          mov pc , lr.global   key_initkey_init: //GPX3_2~5设为输入         //GPX3CON &= ~(0XFFFF<<8) ldr r0 , =GPX3CON          ldr r1 , [r0]         bic r1 , #(0xff<<8)         bic r1 , #(0xff00<<8)         ldr r2 , #0x1111         str r1 , [r0]          mov pc , lr.global  key_stat key_stat:ldr r0 , =GPM3DAT        ldrb r1 , [r0]        mov r1 , r1 , lsr #2        and r1 , #0xf        mov r0 , r1   //将按键状态stat通过r0传给led_on函数,汇编中函数的返回值是通过r0来传递mov pc , lr.global  led_onled_on://点亮led         //GPM4DAT = (GPM4DAT & ~0Xf) | (stat & 0xf) ldr r2 , r0 //将函数唯一的参数stat转移到r2里         ldr r0 , =GPM4DAT         ldrb r1 , [r0]         bic r1 , 0xf         orr r1 , r2  //点灯         strb r1 , [r0]          mov pc , lr/*************************   makefile**************************/TGT := boot.oOBJS := led_key.oOBJC := main.oCROSS_COMPILER := arm-linux-CC := $(CROSS_COMPILER)gcc OBJCOPY := $(CROSS_COMPILER)objcopyCFLAGS := -ffreestandingLDFLAGS : -static -nostartfiles -Ttext=0x40000000all: $(CC) $(CFLAGS) -c $(OBJC:.o=.S) $(OBJC:.o=.c)#替换后缀,编译生成a.out $(CC) $(LDFLAGS) $(OBJC) $(OBJS) #链接,_start在哪个文件里哪个文件链接就放前面 $(OBJCOPY) -O binary a.out $(TGT:.o=.bin)  clean:$(RM) a.out $(OBJC) $(TGT:.o=.bin)