目录
本例程将在鸭嘴兽wifi音视频开发板上学习驱动调试工具devmem2的源码及使用方法。
我们都知道Linux是一款安全性很高的系统,驱动层和用户层有不同的地址空间,应用程序是不能直接访问底层硬件的。但是有一个特例就是devmem,我们利用它可以对物理内存直接读写操作,如查看CPU寄存器的值,这给驱动开发带来了极大的便利。
准备工作:
wifi音视频开发板一块
-
devmem2简介
在Linux开发中常用的调试工具不是很多,devmem2是驱动开发人员常用的调试工具,能够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。
驱动开发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。
2.devmem2应用程序分析
devmem2源代码在\duckbill\N32905\applications\devmem2\devmem2.c,源码如下:
/*
* devmem2.c: Simple program to read/write from/to any location in memory.
*
* Copyright (C) 2000, Jan-Derk Bakker ([email protected])
*
*
* This software has been developed for the LART computing board
* (http://www.lart.tudelft.nl/). The development has been sponsored by
* the Mobile MultiMedia Communications (http://www.mmc.tudelft.nl/)
* and Ubiquitous Communications (http://www.ubicom.tudelft.nl/)
* projects.
*
* The author can be reached at:
*
* Jan-Derk Bakker
* Information and Communication Theory Group
* Faculty of Information Technology and Systems
* Delft University of Technology
* P.O. Box 5031
* 2600 GA Delft
* The Netherlands
*
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
*/
#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';
//小于2个参数,则打印devmen2的usage
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); //获取访问内存的物理地址
if(argc > 2)
access_type = tolower(argv[2][0]); //获取数据类型
//打开设备节点/dev/mem
if((fd = open("/dev/mem", O_RDWR | O_SYNC)) == -1) FATAL;
printf("/dev/mem opened.\n");
fflush(stdout);
//将内核空间映射到用户空间
/* Map one page */
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); //计算出虚拟地址
//根据不同的参数获取不同类型的内存数据
switch(access_type) {
case 'b':
read_result = *((unsigned char *) virt_addr); //读8位的数据
break;
case 'h':
read_result = *((unsigned short *) virt_addr); //读16位的数据
break;
case 'w':
read_result = *((unsigned long *) virt_addr); //读32位的数据
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);
//若参数个数大于3,则表示写入操作
if(argc > 3) {
writeval = strtoul(argv[3], 0, 0); //获取写入的值
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;
}
其实这个工具的源码也比较简单,就是应用程序通过mmap函数将物理内存映射到用户空间虚拟地址,用户层就可以实现对内存的某个地址读写操作了。
3.编译
在ubuntu下切换路径至/duckbill/N32905/applications/devmem2。
执行make,编译生成可执行文件devmem2,devmem2将会自动拷贝至例程文件系统目录 /duckbill/N32905/usr/TEST_mini905/mkFilesys下。
执行例程文件系统TEST_mini905/test_mini905/目录下的脚本mkjffs2.sh,生成我们所需的jffs2文件系统。
4.烧录运行
WIFI-Mini905开发板与电脑之间连接好usb电源线(也充当下载线)、usb转串口线,将拨码开关S1拨向Rec位,按下自锁开关K1,开发板通电,N32905进入烧录模式。
使用TurboWriter依次烧录 开发板光盘资料\Mini905光盘资料\BIN\基础例程下的loader(SpiLoader_905.bin)、内核(Kernel.bin)以及刚刚生成的文件系统(TEST_mini905.jffs2.summary),烧录步骤与例程1一致。
烧录完成后将拨码开关S1拨向Nor位,开发板重新通电,电源指示灯亮,N32905进入正常启动模式,等待系统运行起来。
以下是直接往内存的物理地址0x1直接读写操作。
①读操作
在串口超级终端输入./devmem2 0x1 w,从物理内存地址0x1读出32位的数据为0x1000000。
②写操作
输入./devmem2 0x1 w 0x0,往物理内存地址0x1写0x0。
③读操作
输入./devmem2 0x1 w,从物理内存地址0x1读出的数据为0x0,由此可知,第2步的写操作是正确的。