Linux驱动开发常用调试工具-------之devmem

      在Linux开发中着实用到的调试工具并不是很多。devmem的方式是提供给驱动开发人员，在应用层能够侦测内存地址中的数据变化，以此来检测驱动中对内存或者相关配置的正确性验证。

        devmem2使用方法：

        devmem2 { address } [ type [ data ] ]

                address : 物理地址

                type :要访问的数据类型 : [b]yte, [h]alfword, [w]ord

                data :想要写入的数据，若为读取操作则省略此参数，若为写入，则必须含有此参数。

        如下就贴出devmem2的源代码一探究竟。

#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <string.h>#include <errno.h>#include <signal.h>#include <fcntl.h>#include <ctype.h>#include <termios.h>#include <sys/types.h>#include <sys/mman.h>  #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) {//若参数个数少于两个则打印此工具的使用方法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);if(argc > 2)access_type = tolower(argv[2][0]);    if((fd = open("/dev/mem", O_RDWR | O_SYNC)) == -1) FATAL;    printf("/dev/mem opened.\n");     fflush(stdout);        /* Map one page */ //将内核空间映射到用户空间    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);    //针对不同的参数获取不同类型内存数据    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);        //若参数大于3个，则说明为写入操作，针对不同参数写入不同类型的数据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;}