Linux驱动之定时器在按键去抖中的应用

机械按键在按下的过程中会出现抖动的情况，如下图，这样就会导致本来按下一次按键的过程会出现多次中断，导致判断出错。在按键驱动程序中我们可以这么做：

在按键驱动程序中我们可以这么做来取消按键抖动的影响：当出现一个按键中断后不会马上去处理它，而是延时一个抖动时间（一般10ms），如果在这个时间内再次出现中断那么再次延时10ms。这样循环，一直到在这个10ms内只有一个按键中断，那么就认为这次是真的按键值，然后在定时器处理函数里处理它。上述过程可以利用内核的定时器来实现。

定时器二要素：定时时间、定时时间到后做什么事情。根据这两个要素来编写程序，直接在sixth_drv.c的驱动程序上更改直接看到代码：

1、定时器的创建，先建立一个定时器结构

static struct timer_list buttons_timer;//定义一个定时器

2、在模块装载时初始化定时器

static int sixth_drv_init(void)
{
    /*增加一个定时器用于处理按键抖动*/
    init_timer(&buttons_timer);
    buttons_timer.expires = ;//定时器的定时时间
//    buttons_timer->data = (unsigned long) cs;
    buttons_timer.function = buttons_timeout;//定时时间到后的处理函数
    add_timer(&buttons_timer);//将定义的定时器放入定时器链表

    sixthmajor = register_chrdev(, "buttons", &sixth_drv_ops);//注册驱动程序

    if(sixthmajor < )
        printk("failes 1 buttons_drv register\n");

    sixth_drv_class = class_create(THIS_MODULE, "buttons");//创建类
    if(sixth_drv_class < )
        printk("failes 2 buttons_drv register\n");
    sixth_drv_class_dev = class_device_create(sixth_drv_class, NULL, MKDEV(sixthmajor,), NULL,"buttons");//创建设备节点
    if(sixth_drv_class_dev < )
        printk("failes 3 buttons_drv register\n");

    gpfcon = ioremap(0x56000050, );//重映射
    gpfdat = gpfcon + ;
    gpgcon = ioremap(0x56000060, );//重映射
    gpgdat = gpgcon + ;

    printk("register buttons_drv\n");
    return ;
}

3、编写定时器处理函数

static void buttons_timeout(unsigned long data)
{
    unsigned int pin_val;
    static long cnt=;

    //printk("timeout cnt : %d\n",++cnt);
    if(pin_des==NULL)
        return;
    else
    {
    //    printk("pin_des != NULL\n");

        pin_val = s3c2410_gpio_getpin(pin_des->pin);

        if(pin_val) //按键松开
            key_val = 0x80 | pin_des->key_val;
        else
            key_val = pin_des->key_val;

        wake_up_interruptible(&button_waitq);   /* 唤醒休眠的进程 */
        ev_press = ;    

        kill_fasync(&sixth_fasync, SIGIO, POLL_IN);//发生信号给进程
    }
}

4、当在卸载驱动时将定时器删除；在中断处理程序中直接改变定时器的超时时间，并记录下是哪个按键按下的即可，其他处理都在定时器超时函数中。直接看到完整代码：

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <asm/io.h>        //含有iomap函数iounmap函数
#include <asm/uaccess.h>//含有copy_from_user函数
#include <linux/device.h>//含有类相关的处理函数
#include <asm/arch/regs-gpio.h>//含有S3C2410_GPF0等相关的
#include <linux/irq.h>    //含有IRQ_HANDLED\IRQ_TYPE_EDGE_RISING
#include <asm-arm/irq.h>   //含有IRQT_BOTHEDGE触发类型
#include <linux/interrupt.h> //含有request_irq、free_irq函数
#include <linux/poll.h>
#include <asm-generic/errno-base.h>  //含有各种错误返回值
//#include <asm-arm\arch-s3c2410\irqs.h>

static struct class *sixth_drv_class;//类
static struct class_device *sixth_drv_class_dev;//类下面的设备
static int sixthmajor;

static unsigned long *gpfcon = NULL;
static unsigned long *gpfdat = NULL;
static unsigned long *gpgcon = NULL;
static unsigned long *gpgdat = NULL;

struct fasync_struct *sixth_fasync;

static unsigned int key_val;

struct pin_desc
{
    unsigned int pin;
    unsigned int key_val;
};

static struct pin_desc  pins_desc[] =
{
    {S3C2410_GPF0,0x01},
    {S3C2410_GPF2,0x02},
    {S3C2410_GPG3,0x03},
    {S3C2410_GPG11,0x04}
};

static struct pin_desc *pin_des=NULL;

static unsigned int ev_press;
static DECLARE_WAIT_QUEUE_HEAD(button_waitq);//注册一个等待队列button_waitq

 static atomic_t open_flag = ATOMIC_INIT();     //定义原子变量open_flag 并初始化为1

static DECLARE_MUTEX(button_lock);     //定义互斥锁

static struct timer_list buttons_timer;//定义一个定时器
/*
  *0x01、0x02、0x03、0x04表示按键被按下
  */

/*
  *0x81、0x82、0x83、0x84表示按键被松开
  */

/*
  *利用dev_id的值为pins_desc来判断是哪一个按键被按下或松开
  */
static irqreturn_t buttons_irq(int irq, void *dev_id)
{
    pin_des = (struct pin_desc *)dev_id;//取得哪个按键被按下的状态
    mod_timer(&buttons_timer, jiffies+HZ/);//10ms之后调用定时器处理函数

    return IRQ_HANDLED;
}

static int sixth_drv_open (struct inode * inode, struct file * file)
{
    int ret;

//    if(atomic_dec_and_test(&open_flag)==0)//自检后是否为0,不为0说明已经被人调用
//    {
//        atomic_inc(&open_flag);//原子变量+1
//        return -EBUSY;
//    }
    if(file->f_flags & O_NONBLOCK)//非阻塞方式
    {
        if(down_trylock(&button_lock))//获取信号量失败则返回
            return -EBUSY;
    }
    else
        down(&button_lock);//获得信号量

    ret = request_irq(IRQ_EINT0, buttons_irq, IRQT_BOTHEDGE, "s1", (void * )&pins_desc[]);
    if(ret)
    {
        printk("open failed 1\n");
        return -;
    }
    ret = request_irq(IRQ_EINT2, buttons_irq, IRQT_BOTHEDGE, "s2", (void * )& pins_desc[]);
    if(ret)
    {
        printk("open failed 2\n");
        return -;
    }
    ret = request_irq(IRQ_EINT11, buttons_irq, IRQT_BOTHEDGE, "s3", (void * )&pins_desc[]);
    if(ret)
    {
        printk("open failed 3\n");
        return -;
    }
    ret = request_irq(IRQ_EINT19, buttons_irq, IRQT_BOTHEDGE, "s4", (void * )&pins_desc[]);
    if(ret)
    {
        printk("open failed 4\n");
        return -;
    }

    return ;
}

static int sixth_drv_close(struct inode * inode, struct file * file)
{
//    atomic_inc(&open_flag);//原子变量+1
    up(&button_lock);//释放信号量

    free_irq(IRQ_EINT0 ,(void * )&pins_desc[]);

     free_irq(IRQ_EINT2 ,(void * )& pins_desc[]);

    free_irq(IRQ_EINT11 ,(void * )&pins_desc[]);

    free_irq(IRQ_EINT19 ,(void * )&pins_desc[]);

    return ;
}

static ssize_t sixth_drv_read(struct file * file, char __user * userbuf, size_t count, loff_t * off)
{
    int ret;

    if(count != )
    {
        printk("read error\n");
        return -;
    }

    if(file->f_flags & O_NONBLOCK)//非阻塞方式
    {
        if(!ev_press)//判断是否有按键按下，如果没有直接返回
        {
                key_val = ;
                ret = copy_to_user(userbuf, &key_val, );
                return -EBUSY;
        }
    }
    else//如果没有按键动作，直接进入休眠
        wait_event_interruptible(button_waitq, ev_press);//将当前进程放入等待队列button_waitq中

    ret = copy_to_user(userbuf, &key_val, );
    ev_press = ;//按键已经处理可以继续睡眠

    if(ret)
    {
        printk("copy error\n");
        return -;
    }

    return ;
}

static unsigned int sixth_drv_poll(struct file *file, poll_table *wait)
{
    unsigned int ret = ;
    poll_wait(file, &button_waitq, wait);//将当前进程放到button_waitq列表

    if(ev_press)
        ret |=POLLIN;//说明有数据被取到了

    return ret;
}

static int sixth_drv_fasync(int fd, struct file * file, int on)
{
    int err;
    printk("fansync_helper\n");
    err = fasync_helper(fd, file, on, &sixth_fasync);//初始化sixth_fasync
    if (err < )
        return err;
    return ;
}

static struct file_operations sixth_drv_ops =
{
    .owner   = THIS_MODULE,
    .open    =  sixth_drv_open,
    .read     = sixth_drv_read,
    .release = sixth_drv_close,
    .poll      =  sixth_drv_poll,
    .fasync   = sixth_drv_fasync,

};

static void buttons_timeout(unsigned long data)
{
    unsigned int pin_val;
    static long cnt=;

    //printk("timeout cnt : %d\n",++cnt);
    if(pin_des==NULL)
        return;
    else
    {
    //    printk("pin_des != NULL\n");

        pin_val = s3c2410_gpio_getpin(pin_des->pin);

        if(pin_val) //按键松开
            key_val = 0x80 | pin_des->key_val;
        else
            key_val = pin_des->key_val;

        wake_up_interruptible(&button_waitq);   /* 唤醒休眠的进程 */
        ev_press = ;    

        kill_fasync(&sixth_fasync, SIGIO, POLL_IN);//发生信号给进程
    }
}

static int sixth_drv_init(void)
{
    /*增加一个定时器用于处理按键抖动*/
    init_timer(&buttons_timer);
    buttons_timer.expires = ;//定时器的定时时间
//    buttons_timer->data = (unsigned long) cs;
    buttons_timer.function = buttons_timeout;//定时时间到后的处理函数
    add_timer(&buttons_timer);//将定义的定时器放入定时器链表

    sixthmajor = register_chrdev(, "buttons", &sixth_drv_ops);//注册驱动程序

    if(sixthmajor < )
        printk("failes 1 buttons_drv register\n");

    sixth_drv_class = class_create(THIS_MODULE, "buttons");//创建类
    if(sixth_drv_class < )
        printk("failes 2 buttons_drv register\n");
    sixth_drv_class_dev = class_device_create(sixth_drv_class, NULL, MKDEV(sixthmajor,), NULL,"buttons");//创建设备节点
    if(sixth_drv_class_dev < )
        printk("failes 3 buttons_drv register\n");

    gpfcon = ioremap(0x56000050, );//重映射
    gpfdat = gpfcon + ;
    gpgcon = ioremap(0x56000060, );//重映射
    gpgdat = gpgcon + ;

    printk("register buttons_drv\n");
    return ;
}

static void sixth_drv_exit(void)
{
    del_timer(&buttons_timer);
    unregister_chrdev(sixthmajor,"buttons");

    class_device_unregister(sixth_drv_class_dev);
    class_destroy(sixth_drv_class);

    iounmap(gpfcon);
    iounmap(gpgcon);

    printk("unregister buttons_drv\n");
}

module_init(sixth_drv_init);
module_exit(sixth_drv_exit);

MODULE_LICENSE("GPL");

5、测试代码还是沿用sisth_test.c。将驱动程序和测试程序编译后的文件放入网络文件系统，测试发现不再出现抖动情况。具体过程参考Linux驱动之按键驱动编写（中断方式）