linux字符設備按鍵驅動之防抖動

按鍵驅動程序抖動問題會造成多次中斷髮生，實則可能是一次按下或釋放的操作。本驅動程序就是在按鍵驅動程序（中斷方式）的基礎之上，用定時器來去抖動。

當一次按鍵按下的時候，可能產生多個脈衝，我們可以等到最後一個脈衝平穩時再真正地做按下或釋放的處理。所以，在中斷中我們可以不斷修改定時器的值，當最後穩定下來，沒有中斷產生了，就會調用超時函數，再在超時函數裏面判斷按鍵狀態，返回值給用戶空間等。

定時器的操作：

1.定義timer_list結構體。

2.定義超時函數。

3.在初始化函數綁定定時器結構體和超時函數，初始化定時器結構體等操作。用到

#define setup_timer(timer, fn, data)     \
 do {        \
  static struct lock_class_key __key;   \
  setup_timer_key((timer), #timer, &__key, (fn), (data));\
 } while (0)

這個是在2.6.32內核裏面進行的初始化設置，在低版本中可能包括init和add等操作。

4.在中斷函數裏修改定時器。用到

int mod_timer(struct timer_list *timer, unsigned long expires)

詳細驅動程序如下：

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#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/delay.h>
#include <linux/irq.h>
#include <asm/uaccess.h>
#include <linux/cdev.h>
#include <linux/interrupt.h>
#include <linux/device.h>
#include <linux/sched.h>
#include <linux/gpio.h>

#define SEVENTHDEV MKDEV(250, 0)
struct cdev seventhdrv_cdev;

static struct class 
*seventhdrv_class;

struct button {
    int irq;
    char *name;
    int pin;
    int val;
};

static volatile int pressed 
= 0;
static unsigned char key_val;

struct fasync_struct *button_async;
static struct timer_list seventh_timer;
static struct button *buttonp 
= NULL;
DECLARE_WAIT_QUEUE_HEAD(button_wqh);

/* 六個按鍵的相關定義整合到結構體
*/
static struct button buttons[6]
= {
        {IRQ_EINT8,
"K1", S3C2410_GPG(0), 0x1},
        {IRQ_EINT11,
"K2", S3C2410_GPG(3), 0x2},
        {IRQ_EINT13,
"K3", S3C2410_GPG(5), 0x3},
        {IRQ_EINT14,
"K4", S3C2410_GPG(6), 0x4},
        {IRQ_EINT15,
"K5", S3C2410_GPG(7), 0x5},
        {IRQ_EINT19,
"K6", S3C2410_GPG(11),0x6},
};


static DECLARE_MUTEX(button_lock);

/* 中斷處理函數
*/
static irqreturn_t seventhdrv_intr(int irq, void
*data)
{
    buttonp = 
(struct button*)data;
    mod_timer(&seventh_timer, jiffies+HZ/100);
    return IRQ_RETVAL(IRQ_HANDLED);
}

static int seventhdrv_open(struct inode
* inode, struct file
* file)
{
    int i=6;
     if (file->f_flags
& O_NONBLOCK)
{
        if(down_trylock(&button_lock))
            return -EBUSY;
        } else
{
           down(&button_lock);
        }
    while(i--){
        request_irq(buttons[i].irq,
&seventhdrv_intr, IRQ_TYPE_EDGE_BOTH,
                    buttons[i].name,
&buttons[i]);
    }
    return 0;

}

static ssize_t seventhdrv_read(struct file
*file, char __user
*user, size_t size,loff_t*o)
{
    int sz = sizeof(key_val)
;

    if (sz
!= size)
{
        return -EINVAL;
    }

    if (file->f_flags
& O_NONBLOCK)
    {
        if (!pressed)
            return -EAGAIN;
    }
    else
    {
        /* 如果沒有按鍵動作, 休眠
*/
        wait_event_interruptible(button_wqh, pressed);
    }
    copy_to_user(user,
&key_val, sz);

    /* 重新清除按下標誌
*/
    pressed = 0;

    return sz;
}

static int seventhdrv_close(struct inode
*inode, struct file
*file)
{
    int i=6;

    while(i--)
{
        free_irq(buttons[i].irq,
&buttons[i]);
    }
    up(&button_lock);
    return 0;
}

static struct file_operations seventhdrv_ops =
{
    .owner = THIS_MODULE,
    .open = seventhdrv_open,
    .read = seventhdrv_read,
    .release = seventhdrv_close,
};

static void button_timer(unsigned long data)
{
    int val;
    if (buttonp
== 
NULL) {
        printk(KERN_INFO 
"No button pressed!\n");
        return ;
    }

    val = s3c2410_gpio_getpin(buttonp->pin);

    if (!val)
{/* 按下按鍵*/
        key_val = buttonp->val;
    } else
{ /* 釋放按鍵*/
        key_val = buttonp->val
| 0x10; 
//將第4位置1，做標記
    }

    pressed = 1;
//此處改變按下標誌，以使隊列不繼續睡眠
    wake_up_interruptible(&button_wqh);

    buttonp = 
NULL;
}

static int seventhdrv_init(void)
{
    int ret;
    int devt = SEVENTHDEV;

    ret = register_chrdev_region(devt, 1,
"seventhdrv");
    if (ret)
{
        printk(KERN_ERR 
"Unable to register minors for seventhdrv\n");
        goto fail;
    }
    seventhdrv_class = class_create(THIS_MODULE,
"seventhdrv_class");
    if (IS_ERR(seventhdrv_class))
{
        printk(KERN_ERR 
"can't register device class\n");
        return PTR_ERR(seventhdrv_class);
    }
    device_create(seventhdrv_class,
NULL, devt,
NULL, 
"buttons");
    cdev_init(&seventhdrv_cdev,
&seventhdrv_ops);
    ret = cdev_add(&seventhdrv_cdev, devt, 1);
    if (ret
< 0)
        goto fail_cdev;
    setup_timer(&seventh_timer, button_timer,
(unsigned long)&buttons);
    return 0;

fail_cdev:
    class_unregister(seventhdrv_class);
    device_destroy(seventhdrv_class, devt);
    cdev_del(&seventhdrv_cdev);
fail:
    unregister_chrdev_region(devt, 1);

    return 0;
}

static void seventhdrv_exit(void)
{
    class_unregister(seventhdrv_class);
    device_destroy(seventhdrv_class, SEVENTHDEV);
    cdev_del(&seventhdrv_cdev);
    unregister_chrdev_region(SEVENTHDEV, 1);
}

module_init(seventhdrv_init);
module_exit(seventhdrv_exit);
MODULE_LICENSE("GPL");

應用程序爲：

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#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <signal.h>

int main(int argc, char
*argv[])
{
    int fd, cnt=1;
    unsigned char val;

    fd = open("/dev/buttons", O_RDWR);

    if (fd
< 0)
    {
        printf("Can not open device\n");
        return -1;
    }

    while(1)
    {
        read(fd,
&val, sizeof(unsigned char));
        printf("cnt:%d, val:0x%x\n", cnt++,
val);
    }

    return 0;
}