#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) {
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 */
/* 映射一页的起始地址*/
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);
/* 实际使用的起始偏移的地址*/
virt_addr = map_base + (target & MAP_MASK); //使用的偏移地址限制到1页之内
switch(access_type) {
//读取的数据 转换为不同的数据类型
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;
}根据开发板上的试验，devmem2 这个版本的兼容行对arm平台不是很友好,适用于x86平台, 不适用与arm平台，busybox中提供的devmem对板卡的实用性更好，和兼容性更好
