嵌入式

devmem

2019-07-13 09:24发布

站内文章 / 嵌入式Linux
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内核配置中将CONFIG_DEVMEM选项配置后，会有/dev/mem设备节点，内核对应的驱动代码是drivers/char/mem.c
用户空间程序通过mmap将物理地址映射到用户空间，实现对这些物理地址的读写。 用户空间程序devmem.c #include #include #include #include #include #include #include #include #include #include #include #define FATAL do { fprintf(stderr, "Error at line %d, file %s (%d) [%s] ", __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, " Usage: %s { address } [ type [ data ] ] " " address : memory address to act upon " " type : access operation type : [b]yte, [h]alfword, [w]ord " " data : data to be written ", 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. "); 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. ", 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'. ", access_type); exit(2); } printf("Value at address 0x%X (%p): 0x%X ", 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 ", writeval, read_result); fflush(stdout); } if(munmap(map_base, MAP_SIZE) == -1) FATAL; close(fd); return 0; } 另外在busybox中也有devmem tool，代码的位置在busybox-1.24.1/miscutils/devmem.c ，需要配置CONFIG_USER_BUSYBOX_DEVMEM

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