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四：设备驱动程序

1. 图解–流程

1. 实现供应用程序调用的接口(open/write/read) 操作硬件的代码
2. 向内核注册该驱动程序(以设备号的形式)
3. 创建设备节点(一组绑定的设备名和设备号)

2.设备驱动分类

字符设备：一般以数据(字节)流的形式操作，数据访问有严格顺序

块设备：数据可以随机访问(eg：存储设备)，以块的形式访问数据(类似数组，成块的字节操作)

网络设备：集成复杂的协议栈(eg：网卡) — 按名字维护

3.设备号

设备号：内核维护设备驱动程序的数字(每个设备都有唯一的设备号)

32位：

​ 高12位：主设备号 //区分不同类别的设备

​ 低20位：次设备号 //同类设备的不同设备

#define MKDEV(ma,mi)	((ma)<<8 | (mi))

cat /proc/devices	//查看注册的设备号

4. ctags

sudo app ctags
ctags -R	//追踪文件所属   ctrl + ]  vim界面下，和vscode查找差不多//ctrl + o  返回上次传送前的位置// <p 

5.代码

#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/kdev_t.h>#define MAJOR_NUM 255
#define MINOR_NUM 0
#define DEV_NAME "demo4"static int open(struct inode * node,struct file * file)
{printk("demo4 open.....\n");return 0;
}static ssize_t read(struct file * file,char __user * buf,size_t len,loff_t * offset)
{printk("demo4 read.....\n");return 0;
}static ssize_t write(struct file * file,const char __user * buf,size_t len,loff_t * offset)
{printk("demo4 write.....\n");return 0;
}
static int close(struct inode * node,struct file * file)
{printk("demo4 close.....\n");return 0;
}static dev_t dev_num;
static struct file_operations fops = 
{.owner = THIS_MODULE,.open  = open,.read  = read, .write = write,.release = close
};static struct cdev cdev;static int __init demo_init(void)
{dev_num = MKDEV(MAJOR_NUM, MINOR_NUM);cdev_init(&cdev,&fops);cdev_add(&cdev,dev_num,1);register_chrdev_region(dev_num,1,DEV_NAME);printk("demo4_init ......\n");return 0;
}static void __exit demo_exit(void)
{unregister_chrdev_region(dev_num,1);cdev_del(&cdev);printk("demo4_exit .......\n");
}module_init(demo_init);
module_exit(demo_exit);

#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/kdev_t.h>
#include <asm/io.h>
#include <asm/uaccess.h>#define MAJOR_NUM 253
#define MINOR_NUM 0
#define DEV_NAME "led4"
#define GPBCON 0x56000010 	//虚拟内存硬件不支持，硬件操作实际内存
#define GPBDAT 0x56000014
static volatile unsigned long * gpbcon;
static volatile unsigned long * gpbdat;static void led2_init(void)
{*gpbcon &= ~(0x3 << 12);*gpbcon |= (0x1 << 12);*gpbdat |= (1 << 6);
}static void led2_on(void)
{*gpbdat &= ~(1 << 6);
}static void led2_off(void)
{*gpbdat |= (1 << 6);
}//以下都是函数指针
static int open(struct inode * node, struct file * file)
{led2_init();printk("led4  open ...\n");	//内核打印return 0;
}static ssize_t read(struct file * file, char __user * buf, size_t len, loff_t * offset)
{//copy_to_user();printk("led4 read ...\n");return 0;
}static ssize_t write(struct file * file, const char __user * buf, size_t len, loff_t * offset)
{unsigned char data[10] = {0};unsigned int len_cp = (sizeof(data) < len) ? sizeof(data) : len;ssize_t ret = len_cp;//strcmp(buf,"ledon")//copy_to_user	用户访问copy_from_user(data, buf, len_cp);	//让代码不要在内核空间运行去访问，如果数据有问题，内核访问野指针，内核崩溃if(!strcmp(data, "ledon"))led2_on();else if(!strcmp(data, "ledoff"))led2_off();elseret = -EINVAL;	//EINVAL “-”　返回负，返回非正常值printk("led4 write ...\n");return ret;
}static int close(struct inode * node, struct file * file)
{led2_off();printk("led4 close ...\n");return 0;
}static dev_t dev_num;	//创建设备号
//操作方法
static struct file_operations fops = 
{//结构体都是函数指针，上面函数指针都已经初始化了，//所以赋给对应的结构体中函数指针//gnu中，不像数据结构(windos)一个一个赋值，可以部分初始化.owner = THIS_MODULE,	//指向自己模块，默认.open = open,			//.read = read,.write = write,.release = close
};static struct cdev cdev;	//设备的结构体 （要把设备号和操作方法放进去）　然后在给到内核static int __init led_init(void)	
{int ret = 0;dev_num = MKDEV(MAJOR_NUM, MINOR_NUM);cdev_init(&cdev, &fops);	//cdev_init 把操作方法放进cdev结构体ret = cdev_add(&cdev, dev_num, 1);	//添加几个设备？－－和对应设备号放进cdev结构体if(ret < 0)	//判断int类型goto err_cdev;ret = register_chrdev_region(dev_num, 1, DEV_NAME);	//注册字符设备，注册几个设备号？，设备名字if(ret < 0)goto err_register;gpbcon = ioremap(GPBCON, 4);	//内存映射四个字节，接受对应的物理地址gpbdat = ioremap(GPBDAT, 4);printk("led4_init   ....\n");return ret;err_register:unregister_chrdev_region(dev_num, 1);	//取消注册printk("register_chrdev_region  failed\n");err_cdev:cdev_del(&cdev);	//销毁初始化的cdev结构体printk("cdev_add  failed\n");return ret;	
}static void __exit led_exit(void)
{iounmap(gpbdat);iounmap(gpbcon);unregister_chrdev_region(dev_num, 1);cdev_del(&cdev);printk("led4_exit   ....\n");
}module_init(led_init);	//模块初始化　修饰对应的函数，然后执行对应函数
module_exit(led_exit);	//在操作系统注销时和卸载　　－－　启动和注销

6.手动创建节点/

mknod  /dev/demo  c  255   0		//对应驱动程序/dev/demo    设备节点名
c     字符设备
255   主设备号
0     次设备号

ls /dev
ls /dev -l    

6.1创建应用程序

#include <stdio.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>int main(int argc, const char *argv[])
{int fd = open("/dev/led4",O_RDWR);	////打开对应内核文件if(fd < 0){perror("open demo failed");}unsigned char buf[20] = {0};while(1){write(fd,"ledon",strlen("ledon"));sleep(1);write(fd,"ledoff",strlen("ledoff"));sleep(1);}close(fd);return 0;
}

arm-linux-gcc demo_app.c	//之后在内核运行

7.编译

arm-linux-gcc demo4_app.c在开发板中(minicom) 中	./a.out//为了保护硬件