【linux驱动】嵌入式 Linux 对内存的直接读写（devmem）

devmem工具源码

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

#define FATAL do { fprintf(stderr, "Error at line %d, file %s (%d) [%s]\n", \
  __LINE__, __FILE__, errno, strerror(errno)); exit(1); } while(0)

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

int main(int argc, char **argv) {
    int fd;
    void *map_base, *virt_addr; 
    unsigned long read_result, writeval;
    off_t target;
    int access_type = 'w';

    if(argc < 2) {
        fprintf(stderr, "\nUsage:\t%s { address } [ type [ data ] ]\n"
            "\taddress : memory address to act upon\n"
            "\ttype    : access operation type : [b]yte, [h]alfword, [w]ord\n"
            "\tdata    : data to be written\n\n",
            argv[0]);
        exit(1);
    }
    target = strtoul(argv[1], 0, 0);//转换成无符号的长整型数

    if(argc > 2)
        access_type = tolower(argv[2][0]);//转换成小写


    if((fd = open("/dev/mem", O_RDWR | O_SYNC)) == -1) FATAL;
    printf("/dev/mem opened.\n"); 
    fflush(stdout);

    /* Map one page */ //使用mmap映射一页
    map_base = mmap(0, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, target & ~MAP_MASK);
    if(map_base == (void *) -1) FATAL;
    printf("Memory mapped at address %p.\n", map_base); 
    fflush(stdout);

    virt_addr = map_base + (target & MAP_MASK);
    switch(access_type) {
        case 'b':
            read_result = *((unsigned char *) virt_addr);
            break;
        case 'h':
            read_result = *((unsigned short *) virt_addr);
            break;
        case 'w':
            read_result = *((unsigned long *) virt_addr);
            break;
        default:
            fprintf(stderr, "Illegal data type '%c'.\n", access_type);
            exit(2);
    }
    printf("Value at address 0x%X (%p): 0x%X\n", target, virt_addr, read_result); 
    fflush(stdout);

    if(argc > 3) {
        writeval = strtoul(argv[3], 0, 0);
        switch(access_type) {
            case 'b':
                *((unsigned char *) virt_addr) = writeval;
                read_result = *((unsigned char *) virt_addr);
                break;
            case 'h':
                *((unsigned short *) virt_addr) = writeval;
                read_result = *((unsigned short *) virt_addr);
                break;
            case 'w':
                *((unsigned long *) virt_addr) = writeval;
                read_result = *((unsigned long *) virt_addr);
                break;
        }
        printf("Written 0x%X; readback 0x%X\n", writeval, read_result); 
        fflush(stdout);
    }

    if(munmap(map_base, MAP_SIZE) == -1) FATAL;
    close(fd);
    return 0;
}

devmem使用方法

root@myzr:~# ./devmem
Usage:  ./devmem { address } [ type [ data ] ]
    address : memory address to act upon
    type    : access operation type : [b]yte, [h]alfword, [w]ord
    data    : data to be written

查看寄存器地址

root@myzr:~# ./devmem  0x20e05e0
/dev/mem opened.
Memory mapped at address 0x76f99000.
Value at address 0x20E05E0 (0x76f995e0): 0x1B8B1

写寄存器

root@myzr:~# ./devmem 0x209c000 b 1
/dev/mem opened.
Memory mapped at address 0x76f25000.
Value at address 0x209C000 (0x76f25000): 0x5C
Written 0x1; readback 0x5C
root@myzr:~#