C语言和ARM汇编混合编程实现阶乘运算

2. 通过C语言调用阶乘运算结果并显示出来。

（1）    用汇编语言编写阶乘运算子程序，命名为zmc.s;

程序如下：

AREA asmfile,CODE,READONLY

  EXPORT asmDouble

asmDouble

     sub R1,R0,#1

     cmp R1,#00

     BEQ L2

L1  mul R2,R0,R1

    sub R1,R1,#1

    mov R0,R2

    cmp R1,#00

    BNE L1

L2  mov pc, lr

END

（2）    将其添加到半主机程序中的SYS中；

（3）    将半主机程序的main修改如下：

#include "def.h"

#include "44b.h"

#include "stdio.h"

#include "sys_lcd.h"

extern int asmDouble(int a);

void Delay(int time)

{

       volatile int i,j;

       i = 0;

       j = 0;

       for(i = 0; i

       {

              j = 0;

          while(j++<30)

                  ;

       }

}

struct __FILE

{

       int handle;

};

FILE __stdout, __stdin;

void UART_Init(int baud)

{

    rUFCON0=0x0;     // FIFO disable

    rUFCON1=0x0;

    rUMCON0=0x0;

    rUMCON1=0x0;

    rULCON0=0x3;       // UART0

    rUCON0=0x245;

    rUBRDIV0=( (int)(MCLK/16./baud + 0.5) -1 );

    rULCON1=0x3;       // UART1

    rUCON1=0x245;

    rUBRDIV1=( (int)(MCLK/16./baud + 0.5) -1 );

       Delay(10);

}

#define SemiSWI 0x123456

__swi(SemiSWI) void _WriteC(unsigned op, char *c);

#define WriteC(c) _WriteC(0x3,c)

__swi(SemiSWI) unsigned char _ReadC(unsigned op, char val);

#define ReadC() _ReadC(0x7,0)

__swi(SemiSWI) void _Exit(unsigned op, unsigned except);

#define Exit() _Exit(0x18,0x20026)

void UART_PutChar(unsigned char data)

{    

       rUTXH0=data;

       while(!(rUTRSTAT0 & 0x2))

              ;

}    

char UART_GetChar(void)

{

       while(!(rUTRSTAT0 & 0x1))

              ;

       return rURXH0;

}

extern void LCD_PutChar(unsigned char data);

int fputc(int ch, FILE *f)

{    

       char tempch = ch;

           WriteC( &tempch );

       return ch;

}

int fgetc(FILE *f)

{

    unsigned char tempch;

    tempch = ReadC();

    return tempch;

}

int ferror(FILE *f)

{

       return EOF;

}

void _sys_exit(int return_code)

{

    Exit();         /* for debugging */

label:  goto label; /* endless loop */

}

int main(void)

{

       int a;

       int b;

       Port_Init();

       IO82C55A_Init();

       UART_Init(115200);

       LCD_Init();

       LCD_ChangeMode(DspTxtMode);

       LCD_Printf("Hello World!\n");

while(1)

{

              printf("Hello! Please Input N: \n\n"); 

 LCD_Printf("Hello! Please Input N: \n\n");   

       scanf("%d",&a);

                            b=asmDouble(a);

              printf("%d!=%d\n",a,b);

 LCD_Printf("%d!=%d\n",a,b);   

              }

              }

（4）    调试观察结果：

显示：Hello! Please Input N:

      输入5

显示5！=120；

输入3!=6;

结果正确。