mmap直接控制底层【转】

转自：http://blog.csdn.net/xyyangkun/article/details/7830149

版权声明：本文为博主原创文章，未经博主允许不得转载。

这是在mini6410上测试成功的，在没有驱动的情况下用程序直接控制了led灯test_mmap.c：

/* Example how to access the value of the on-board DIP switches on
 * HiCO.SH7760. You can compile the program with command:
 *
 *   sh4-linux-gcc -Wall dip_switch.c -o dip_switch
 */
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/mman.h>

#define MAP_SIZE 4096UL
#define MAP_MASK (MAP_SIZE - 1)


int main(void) {
    int fd;
    void *map_base, *virt_addr;

    /* Physical address of the DIP switch GPIO register on HiCO.SH7760 (See
     * the HiCO.SH7760 hardware manual
     *
     * _NOTE_: the dipswitches also define how the system boots (i.e. the value
     * is used by the bootloader at startup), so oafter testting, leave the
     * switches in the same position as they were */
    off_t target = 0x7F008800;  //GPKCON0 0x7F008800

    if((fd = open("/dev/mem", O_RDWR | O_SYNC)) == -1) {
        printf("/dev/mem could not be opened.
");
    perror("open");
        exit(1);
    } else {
        printf("/dev/mem opened.
");
    }

    /* Map one page */
    map_base = mmap(0, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, target & ~MAP_MASK);
    if(map_base == (void *) -1) {
        printf("Memory map failed.
");
    perror("mmap");
    } else {
        printf("Memory mapped at address %p.
", map_base);
    }

    virt_addr = map_base + (target & MAP_MASK);

    /* acess remapped region here */

    printf("Now try to change the value of the on-board DIP switche
");
    *(unsigned int *)virt_addr=0x11110000;//0x1111<<16;//设定为输出状态
    int ab=*(unsigned int *)virt_addr;
    //*(unsigned int *)(virt_addr+8)=0xffffffff;
    printf("ab=%x
",ab);

#if 1
    while(1){
    *(volatile unsigned int *)(virt_addr+8)=0x00;   //一定要是virt_addr不能是map_base//置０亮
    printf("1value is 0x%x
",*(unsigned int *)(virt_addr+8));
    printf("2value is 0x%x
",*(unsigned int *)virt_addr);
    sleep(1);   //一定要有要不很快，人眼发现不了
    *(volatile unsigned int *)(virt_addr+8)=0xf0;　　　　　　　　　　　　　　　　　　//置１灭
    printf("3value is 0x%x
",*(unsigned int *)(virt_addr+8));
    printf("4value is 0x%x
",*(unsigned int *)virt_addr);
    sleep(1);   //一定要有要不很快，人眼发现不了
    }
 #endif
    /* we'll never get here in this example, but here's how the region is
     * unmapped. */
    if(munmap(map_base, MAP_SIZE) == -1) {
        printf("Memory unmap failed.
");
    }

    close(fd);
}

以上程序证明了在linux下用mmap函数可以在没有驱动的情况下也可以直接控制底层。

网上说只能控制gpio设备，我还可以直接控制其它设备，有待验证。