Linux驱动开发常用调试工具-------之devmem

查看dtb头四个字节数据

dtb 地址 uboot

#define AMBOOT_TAG_OFFSET (0x00000100)

#define AMBOOT_DTB_ADDR(k) (((k) & (~SIZE_1MB_MASK)) + AMBOOT_TAG_OFFSET)

rval = flprog_get_dtb((u8 *)AMBOOT_DTB_ADDR(KERNEL_RAM_START));

/dav/test # devmem 0x00200100 32

0xEDFE0DD0

与实际r6.dtb文件内容一致

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。

[cpp] view
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#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;

}