一、概述
Linux内核就是由各种驱动组成的，内核源码中大约有85%的各种渠道程序的代码。一般来说，编写Linux设备驱动大致流程如下：
1、查看原理图，数据手册，了解设备的操作方法。
2、在内核中找到相近的驱动程序，以它为模板开发。
3、实现驱动的初始化：比如像内核注册这个驱动程序
4、设计要实现的操作：open，close，read，write等
5、实现中断服务（不是必须的）
6、编译该驱动程序到内核中，或insmod命令加载
7、测试驱动程序。
二、驱动程序的加载与卸载
module_init(my_init);
module_exit(my_clearup);
三、字符设备驱动程序主要的数据结构
1、系统调用：应用程序不能直接操作硬件，而是使用统一的接口函数调用硬件驱动程序。这些接口成为系统调用。在库函数中定义了，可以在gilbc的fcntl.h, unistd.h,sys/ioctl.h 等文件找到。open，wirite，read等。
2、数据结构file_operations是在内核中的，在include/linux/fs.h中。定义如下：
/*
* NOTE:
* read, write, poll, fsync, readv, writev, unlocked_ioctl and compat_ioctl
* can be called without the big kernel lock held in all filesystems.
*/
struct file_operations {
struct module *owner;
loff_t (*llseek) (struct file *, loff_t, int);
ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
int (*readdir) (struct file *, void *, filldir_t);
unsigned int (*poll) (struct file *, struct poll_table_struct *);
int (*ioctl) (struct inode *, struct file *, unsigned int, unsigned long);
long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
int (*mmap) (struct file *, struct vm_area_struct *);
int (*open) (struct inode *, struct file *);
int (*flush) (struct file *, fl_owner_t id);
int (*release) (struct inode *, struct file *);
int (*fsync) (struct file *, struct dentry *, int datasync);
int (*aio_fsync) (struct kiocb *, int datasync);
int (*fasync) (int, struct file *, int);
int (*lock) (struct file *, int, struct file_lock *);
ssize_t (*sendfile) (struct file *, loff_t *, size_t, read_actor_t, void *);
ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);
unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
int (*check_flags)(int);
int (*dir_notify)(struct file *filp, unsigned long arg);
int (*flock) (struct file *, int, struct file_lock *);
ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *, size_t, unsigned int);
ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int);
};
3、设备的主次设备号-=
内核靠这个寻找对应的驱动程序。应用程序在操作设备文件时，Linux系统就会根据设备文件的类型，主设备号在内核中注册的file_operation（对于块设备号是block_device_operations结构），次设备号来分辨它是同类设备中的第几个。
4、注册函数与卸载函数
register_chrdev；unregister_chrdev;
四、LED驱动程序
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/delay.h>
#include <asm/uaccess.h>
#include <asm/irq.h>
#include <asm/io.h>
#include <asm/arch/regs-gpio.h>
#include <asm/hardware.h> //定义寄存器
volatile unsigned long *gpfcon=NULL;
volatile unsigned long *gpfdat=NULL; static struct class *myFirD_class;//为了能自动创建mdev
static struct class_device *myFirD_class_dev; //打开
static int myFirD_open(struct inode *inode, struct file *file)
{
printk("myFirD has open\n");
//配置IO口
*gpfcon &= ~((0x3<<(*)) | (0x3<<(*)) | (0x3<<(*)));//相与
*gpfcon |= ((0x1<<(*)) | (0x1<<(*)) | (0x1<<(*)));//相或
return ;
}
//写
static ssize_t myFirD_write(struct file *file, const char __user *buf, size_t count, loff_t * ppos)
{
int val; //printk("first_drv_write\n"); copy_from_user(&val, buf, count); // copy_to_user(); if (val == )
{
// 点灯
*gpfdat &= ~((<<) | (<<) | (<<));
}
else
{
// 灭灯
*gpfdat |= (<<) | (<<) | (<<);
} return ;
}
//定义一个结构
static struct file_operations myFirD_fops = {
.owner = THIS_MODULE, /* 这是一个宏，推向编译模块时自动创建的__this_module变量 */
.open = myFirD_open,
.write = myFirD_write,
};
//需要用函数把结构告诉内核。注册驱动程序
int major; //主设备号
int myFirD_init(void)
{
major=register_chrdev(,"myFirD",&myFirD_fops);//告诉内核
myFirD_class = class_create(THIS_MODULE, "myFirD");//建个类
//设备
myFirD_class_dev = class_device_create(myFirD_class, NULL, MKDEV(major, ), NULL, "xyz");
gpfcon=(volatile unsigned *)ioremap(0x56000050,);
gpfdat = gpfcon + ;;
return ;
}
void myFirD_exit(void)
{
unregister_chrdev(major,"myFirD");//告诉内核 class_device_unregister(myFirD_class_dev);
class_destroy(myFirD_class);
iounmap(gpfcon);
}
module_init(myFirD_init);
module_exit(myFirD_exit);
MODULE_LICENSE("GPL");
五、Makefile文件
KERN_DIR = /work/system/linux-2.6.22.6#内核所在的目录 all:
make -C $(KERN_DIR) M=`pwd` modules clean:
make -C $(KERN_DIR) M=`pwd` modules clean
rm -rf modules.order obj-m += myFirD.o