简单字符设备驱动程序
理论知识参考Linux Device Driver, 3rd Edition。实验中使用主动分配主设备号，按照LDD3中说的最好是自动分配设备号，这里只是为了理解。
实验步骤如下：
（1）使用cat/proc/device查看字符设备主设备号，这里假设50主设备号没有使用而在本设备中使用。
创建字符设备文件节点：mknod/dev/mycdev c 50 0
修改设备文件权限：chmod 777/dev/mycdev
其中的mycdev为步骤（2）中要安装的模块名。
（2）编写驱动程序：注意代码中 #define MYCDEV_MAJOR (50)
/* =====================================================================
* Filename: mycdev.c
*
* Description:
*
* Version: 1.0 (02/26/2013)
* Created: xhzuoxin([email protected])
* Compiler: gcc
*======================================================================
*/
#include<linux/init.h>
#include<linux/module.h>
#include<linux/types.h>
#include<linux/fs.h>
#include<linux/mm.h>
#include<linux/sched.h>
#include<linux/cdev.h>
#include<asm/system.h>
#include<asm/io.h>
#include<asm/uaccess.h>
#include<linux/kernel.h>
#include<linux/errno.h>
#include<linux/slab.h>
MODULE_LICENSE("GPL");
#defineMYCDEV_MAJOR (50)
#defineMYCDEV_SIZE 0x1000
staticdev_t mycdev_major = MYCDEV_MAJOR;
structmycdev {
struct cdev cdev;
unsigned charmem[255];
};
//struct mycdev dev;
structmycdev *devp;
static int mycdev_open(structinode *inode, struct file *fp)
{
fp->private_data= devp;
return 0;
}
static int mycdev_release(structinode *inode, struct file *fp)
{
return 0;
}
staticssize_t mycdev_read(struct file *fp, char __user *buf, size_t size, loff_t *pos)
{
unsigned long p =*pos;
unsigned int count =size;
struct mycdev *tmp_dev = fp->private_data;
if (p >= MYCDEV_SIZE) {
return -1;
}
if (count > MYCDEV_SIZE - p) {
count =MYCDEV_SIZE - p;
}
if (copy_to_user(buf, (void*)(tmp_dev->mem + p), count) != 0) {
printk("read error!\n");
return -1;
} else {
*pos +=count;
printk(KERN_INFO"read %d bytes from %ld\n", count, p);
}
return count;
}
staticssize_t mycdev_write(struct file *fp, const char __user*buf, size_t size, loff_t *pos)
{
unsigned long p =*pos;
unsigned int count =size;
struct mycdev *tmp_dev = fp->private_data;
if (p > MYCDEV_SIZE) {
return -1;
}
if (p > MYCDEV_SIZE - count) {
count =MYCDEV_SIZE - p;
}
if (copy_from_user((void*)(tmp_dev->mem + p), buf, count) != 0) {
return -1;
} else {
*pos +=count;
printk(KERN_INFO"write %d bytes from %ld\n", count, p);
}
return count;
}
staticloff_t mycdev_llseek(struct file *fp, loff_toff, int whence)
{
// structmycdev *dev = fp->private_data;
loff_tnew_pos = 0;
switch(whence) {
case SEEK_SET:
new_pos= off;
break;
case SEEK_CUR:
new_pos= fp->f_pos + off;
break;
case SEEK_END:
new_pos= MYCDEV_SIZE + off;
}
if (new_pos < 0) {
return -EINVAL;
} else {
fp->f_pos= new_pos;
return new_pos;
}
}
/* paddingg struct file operation */
static const structfile_operations mycdev_fops = {
.owner =THIS_MODULE,
.read =mycdev_read,
.write =mycdev_write,
.open =mycdev_open,
.release =mycdev_release,
.llseek =mycdev_llseek,
};
static void setup_mycdev(structmycdev *dev, int index)
{
int ret;
int devno = MKDEV(mycdev_major, index);
cdev_init(&dev->cdev,&mycdev_fops);
dev->cdev.owner= THIS_MODULE;
dev->cdev.ops= &mycdev_fops;
ret =cdev_add(&dev->cdev, devno, 1);
if (ret) {
printk("adding mycdev error!\n");
}
}
static int __init mycdev_init(void)
{
int ret;
dev_tdevno = 0;
if (mycdev_major) { /* 静态分配*/
devno =MKDEV(mycdev_major, 0);
ret =register_chrdev_region(devno, 1, "mycdev");
} else { /* 动态分配 */
ret =alloc_chrdev_region(&devno, 0, 1, "mycdev");
mycdev_major= MAJOR(devno);
}
devp =kmalloc(sizeof(structmycdev), GFP_KERNEL);
if (!devp) {
ret =-ENOMEM;
unregister_chrdev_region(devno,1);
return ret;
}
memset(devp,0, sizeof(structmycdev));
setup_mycdev(devp,0);
return 0;
}
static void __exit mycdev_exit(void)
{
printk("mycdev module is leaving...\n");
cdev_del(&devp->cdev);
kfree(devp);
unregister_chrdev_region(MKDEV(mycdev_major,0), 1);
}
module_init(mycdev_init);
module_exit(mycdev_exit);
此次测试分别在x86平台和Tiny6410平台，Tiny6410平台下的Makefile如下：
ARCH=arm
COMPILE=arm-linux-
ifneq ($(KERNELRELEASE),)
obj-m:=mycdev.o
else
# 已经构建好(执行过:make zImage)的Tiny6410内核树目录
KDIR ?= /mnt/HappyStudy/Tiny6410/linux-2.6.38
PWD := $(shell pwd)
endif
all:
make -C$(KDIR) M=$(PWD) modules ARCH=$(ARCH) CROSS_COMPILE=$(COMPILE)
clean:
rm -f *.ko*.o *.mod.o *.od.c *.symvers
x86平台下的Makefile如下：
ifneq ($(KERNELRELEASE),)
obj-m:=mycdev.o
else
KDIR ?= /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)
endif
all:
make -C$(KDIR) M=$(PWD) modules
CROSS_COMPILE=$(COMPILE)
clean:
rm -f *.ko*.o *.mod.o *.od.c *.symvers
在PC机上make，通过NFS共享或ftp下载到Tiny6410开发板上执行insmodmycdev.ko（超级终端输入）。
注：为了能使用交叉编译，必须在PC机上配置好Tiny6410对应操作系统的内核树。内核树的配置过程如下：
—— 进入源代码目录下
—— cp config_mini6410_s70 .config， makemenuconfig
—— make zImage
—— make modules
我们PC上使用的CentOS环境已经将源码树配置好了，Linux源码在/usr/src目录下，已编译的模块在/lib/modules目录下，这就是在编写PC上驱动程序不用配置而编写嵌入式驱动需要配置内核树的原因。
（3）编写用户态的测试程序如下：
/*
*=======================================================================
* Filename: usr_test.c
*
* Description:
*
* Version: 1.0 (02/26/2013)
* Created: xhzuoxin([email protected])
* Compiler: gcc
*=======================================================================
*/
#include<stdio.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<stdlib.h>
intmain(void)
{
int testdev;
int n, i, ret;
char write_buf[] = "xiahouzuoxin";
char buf[12];
testdev =open("/dev/mycdev", O_RDWR);
if (testdev == -1) {
printf("cannot open file.\n");
exit(1);
}
n = sizeof(write_buf)/sizeof(char);
if (ret = write(testdev, write_buf, n) < n) {
printf("write error!\n");
exit(1);
}
// close(testdev);
// testdev =open("/dev/mycdev", O_RDWR);
lseek(testdev,0, SEEK_SET);
if (testdev == -1) {
printf("cannot open file.\n");
exit(1);
}
if (ret = read(testdev, buf, n) < n) {
printf("read error!\n");
exit(1);
}
for (i=0; i<n; i++) {
printf("%c", buf[i]);
}
printf("\n");
close(testdev);
return 0;
}
在PC机上使用arm-linux-gcc usr_test.c –ousr_test编译，通过NFS共享或ftp下载到Tiny6410开发板上执行./usr_test（超级终端输入）。