字符设备之中断按键

从题目就可以意会到这一节还是关于字符设备的驱动，不过是另一种技巧：中断。这个词一点都不陌生。

一、先来分析今天的重量级函数request_irq()，看看他的函数原型就行了，先不进行深入分析。

int request_irq(unsigned int irq, irq_handler_t handler, unsigned long flags,const char *name, void *dev_id);

关键是参数的意义：

①irq:中断号，在irqs.h中定义，每一条中断线上面对应一个中断号，用来在irq_src[]中索引中断描述符
②handler:中断处理函数
③flags:中断触发方式设置，在include/linux/irq.h文件中定义
④name:中断设备名，open中断设备之后可以通过cat proc/interrupts查看
⑤dev_id:是设备id，他是个空类型，可转化成任何类型，值得探讨他的作用，概括为下面两点：

第一：dev_id参数会在发生中断时传递给该中断的服务程序。

每一个设备通常都会有自己特有的结构体，通过“void *dev_id”就可以将其挂接到一个irqaction结构中，给这个结构体中的handler函数使用，主要在共享中断中对判断设备自身是否有中断触发起作用。这时需要回忆一下内核中断处理体系结构。顺便看看下面irqaction结构体成员。

struct irqaction {irq_handler_t handler;//@handler:interrupt handler functionunsigned long flags;//@flags:flags (see IRQF_* above)cpumask_t mask;//@mask:no comment as it is useless and about to be removedconst char *name;//@name:name of the devicevoid *dev_id;//@dev_id:cookie to identify the devicestruct irqaction *next;//@next:pointer to the next irqaction for shared interruptsint irq;//@irq:interrupt numberstruct proc_dir_entry *dir;//@dir:pointer to the proc/irq/NN/name entryirq_handler_t thread_fn;//@thread_fn:interupt handler function for threaded interruptsstruct task_struct *thread;//@thread:thread pointer for threaded interruptsunsigned long thread_flags;//@thread_flags:flags related to @thread};

第二：在使用free_irq函数释放dev_id对应的irqaction结构时使用。因为每一个设备dev_id都是独特的，看看free_irq源码就知道了

void free_irq(unsigned int irq, void *dev_id){kfree(__free_irq(irq, dev_id));}static struct irqaction *__free_irq(unsigned int irq, void *dev_id){struct irq_desc *desc = irq_to_desc(irq);//获取该中断号对应的irq_desc[irq]结构体struct irqaction *action, **action_ptr;struct task_struct *irqthread;unsigned long flags;WARN(in_interrupt(), "Trying to free IRQ %d from IRQ context!\n", irq);if (!desc)return NULL;spin_lock_irqsave(&desc->lock, flags);/* * There can be multiple actions per IRQ descriptor, find the right * one based on the dev_id: */action_ptr = &desc->action;<span style="white-space:pre"></span>//找到irq中断号对应的irqaction链表for (;;) { <span style="white-space:pre"></span>//循环遍历irqaction链表，比较dev_id成员action = *action_ptr;if (!action) {WARN(1, "Trying to free already-free IRQ %d\n", irq);spin_unlock_irqrestore(&desc->lock, flags);return NULL;}if (action->dev_id == dev_id)<span style="white-space:pre"></span>//判断是否找到相应dev_id设备的irqaction break;action_ptr = &action->next;<span style="white-space:pre"></span>//指向下一个irqaction结构体}/* Found it - now remove it from the list of entries: */*action_ptr = action->next;/* If this was the last handler, shut down the IRQ line: */if (!desc->action) {desc->status |= IRQ_DISABLED;if (desc->chip->shutdown)desc->chip->shutdown(irq);elsedesc->chip->disable(irq);}irqthread = action->thread;action->thread = NULL;spin_unlock_irqrestore(&desc->lock, flags);unregister_handler_proc(irq, action);/* Make sure it's not being used on another CPU: */synchronize_irq(irq);if (irqthread) {if (!test_bit(IRQTF_DIED, &action->thread_flags))kthread_stop(irqthread);put_task_struct(irqthread);}return action; <span style="white-space:pre"></span>//将找到的irqaction结构体成员返回给上一层调用kfree()函数释放掉这个结构体}

二、今天的字符设备中断按键程序：buttons.c，文中已附代码注释

#include <linux/delay.h>#include <linux/irq.h>#include <asm/uaccess.h>#include <asm/irq.h>#include <asm/io.h>#include <linux/module.h>#include <linux/device.h> //class_create#include <mach/regs-gpio.h>//S3C2410_GPF1 #include <mach/hardware.h>#include <linux/interrupt.h>  //wait_event_interruptible#include <linux/fs.h>/* 定义并初始化等待队列头 */static DECLARE_WAIT_QUEUE_HEAD(button_waitq);static struct class *buttondev_class;static struct device *buttons_device;static struct pin_desc{unsigned int pin;unsigned int key_val;};static struct pin_desc pins_desc[4] = {{S3C2410_GPF1,0x01}, //S3C2410_GPF1是对GPF1引脚这种“设备”的编号dev_id{S3C2410_GPF4,0x02},{S3C2410_GPF2,0x03},{S3C2410_GPF0,0x04},}; static int ev_press = 0;static unsigned char key_val;int major;/* 中断处理函数 */static irqreturn_t handle_irq(int irq, void *dev_id){struct pin_desc *irq_pindesc = (struct pin_desc *)dev_id;//unsigned int pinval;pinval = s3c2410_gpio_getpin(irq_pindesc->pin);//获取按键值:有按键按下返回按键值0/* 键值: 按下时, 0x01, 0x02, 0x03, 0x04 *//* 键值: 松开时, 0x81, 0x82, 0x83, 0x84 */if(pinval){/* 松开 */key_val = 0x80 | (irq_pindesc->key_val);}else{/* 按下 */key_val = irq_pindesc->key_val;}ev_press = 1;/* 表示中断已经发生 */wake_up_interruptible(&button_waitq);   /* 唤醒休眠的进程 */return IRQ_HANDLED;}static int buttons_dev_open(struct inode * inode, struct file * filp){/*  K1-EINT1,K2-EINT4,K3-EINT2,K4-EINT0   *  配置GPF1、GPF4、GPF2、GPF0为相应的外部中断引脚   *  IRQT_BOTHEDGE应该改为IRQ_TYPE_EDGE_BOTH */request_irq(IRQ_EINT1, handle_irq, IRQ_TYPE_EDGE_FALLING, "K1",&pins_desc[0]);request_irq(IRQ_EINT4, handle_irq, IRQ_TYPE_EDGE_FALLING, "K2",&pins_desc[1]);request_irq(IRQ_EINT2, handle_irq, IRQ_TYPE_EDGE_FALLING, "K3",&pins_desc[2]);request_irq(IRQ_EINT0, handle_irq, IRQ_TYPE_EDGE_FALLING, "K4",&pins_desc[3]);return 0;}static int buttons_dev_close(struct inode *inode, struct file *file){free_irq(IRQ_EINT1,&pins_desc[0]);free_irq(IRQ_EINT4,&pins_desc[1]);free_irq(IRQ_EINT2,&pins_desc[2]);free_irq(IRQ_EINT0,&pins_desc[3]);return 0;}static ssize_t buttons_dev_read(struct file *file, char __user *user, size_t size,loff_t *ppos){if (size != 1)return -EINVAL;/* 当没有按键按下时，休眠。 * 即ev_press = 0; * 当有按键按下时，发生中断，在中断处理函数会唤醒 * 即ev_press = 1;  * 唤醒后，接着继续将数据通过copy_to_user函数传递给应用程序 */wait_event_interruptible(button_waitq, ev_press);copy_to_user(user, &key_val, 1);/* 将ev_press清零 */ev_press = 0;return 1;}/* File operations struct for character device */static const struct file_operations buttons_dev_fops = {.owner= THIS_MODULE,.open= buttons_dev_open,.read= buttons_dev_read,.release    = buttons_dev_close,};/* 驱动入口函数 */static int buttons_dev_init(void){/* 主设备号设置为0表示由系统自动分配主设备号 */major = register_chrdev(0, "buttons_dev", &buttons_dev_fops);/* 创建buttondev类 */buttondev_class = class_create(THIS_MODULE, "buttondev");/* 在buttondev类下创建buttons设备，供应用程序打开设备*/buttons_device = device_create(buttondev_class, NULL, MKDEV(major, 0), NULL, "buttons");//return 0;}/* 驱动出口函数 */static void buttons_dev_exit(void){unregister_chrdev(major, "buttons_dev");device_unregister(buttons_device);<span style="white-space:pre"></span>//卸载类下的设备class_destroy(buttondev_class);<span style="white-space:pre"></span>//卸载类}/* 模块加载和卸载函数的修饰 */module_init(buttons_dev_init);  module_exit(buttons_dev_exit); MODULE_AUTHOR("CLBIAO");MODULE_DESCRIPTION("Just for Demon");MODULE_LICENSE("GPL");  //遵循GPL协议

三、应用程序：app_irq.c

/* 文件的编译指令是arm-linux-gcc -static -o app_irq app_irq.c */#include <sys/types.h>#include <sys/stat.h>#include <fcntl.h>#include <stdio.h>int main(int argc, char **argv){int fd;unsigned char key_val;fd = open("/dev/buttons", O_RDWR); //申请外部引脚中断服务if (fd < 0){printf("can't open!\n");}while (1){read(fd, &key_val, 1); //读出按键值printf("key_val = 0x%x\n", key_val);}return 0;}

实验测试结果：

四、小结：字符设备驱动中断编程框架：

①定义并初始化等待队列头
static DECLARE_WAIT_QUEUE_HEAD(xxx_waitq);
②/驱动入口函数
static int xxx_dev_init(void);
module_init(xxx_dev_init);
③驱动出口函数
static void xxx_dev_exit(void);
module_exit(xxx_dev_exit);
④打开中断设备时注册中断
static int xxx_dev_open(struct inode * inode, struct file * filp)
{

...

request_irq(irq, handle_irq, IRQ_TYPE_XXX, "dev_name",dev_id);//dev_id通常是结构体指针

...

}
⑤关闭中断时释放中断资源
static int xxx_dev_close(struct inode *inode, struct file *file)
{

...

free_irq(irq,dev_id);

...

}
⑥中断处理函数#核心#
static irqreturn_t handle_irq(int irq, void *dev_id)
{

/* (1)通常是读某个寄存器或IO引脚分辨中断源 */

/* (2)进行中断处理 */

/* (3)唤醒休眠的进程--她还在静静地等着你凯旋归来呢 */

wake_up_interruptible(&button_waitq); 

return IRQ_HANDLED;

}

⑦根据需要，如果用户程序需要获取中断发生时的某些信息来个read函数
static ssize_t buttons_dev_read(struct file *file, char __user *user, size_t size,loff_t *ppos)
{

...

wait_event_interruptible(xxx_waitq, ev_flag);//ev_flag=0表示中断未发生，还没有可读资源，进入睡眠

copy_to_user(user, &data, 1);//将数据读到用户空间

ev_flag = 0;// 将ev_flag清零

return 1;

}
⑧遵守的规则
MODULE_AUTHOR("CLBIAO");
MODULE_DESCRIPTION("Just for Demon");
MODULE_LICENSE("GPL");  //遵循GPL协议