Linux嵌入式驱动学习之路(十五)按键驱动-定时器防抖

　　在之前的定时器驱动程序中，我们发现在连续按下按键的时候，正常情况下应该是一次按下对应一次松开。而程序有时候会显示是两次按下，一次松开。这个问题是因为在按下的时候，因为是机械按键，所以电压信号会产生一定的波动，会让程序进行两次中断，如何解决这个问题呢？

　　我们可以在发生一次中断之后等待一段时间再去判断按键是否已经被按下，如果是已经被按下了 则本次有效，否则无效。这里用到了定时器。

定时器常用的操作函数有：

  init_timer(&timer);   　　　　　　　　//定时器初始化
  timer.data=10;        　　　　　　　　//设置超时处理函数参数
  timer.expires=jiffies+(10*HZ);   　 //设置超时jiffies值为10s  
  timer.function=timer_func; 　　　　　//设置超时处理函数
  add_timer(&timer);      　　　　　　 //添加定时器到内核
  del_timer(&timer);   　　　　　　　　 //删除定时器  在每次调用之前应该把上次调用的删除

驱动代码：

#include <linux/sched.h>
#include <linux/signal.h>
#include <linux/spinlock.h>
#include <linux/errno.h>
#include <linux/random.h>
#include <linux/poll.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/wait.h>
#include <linux/mutex.h>
#include <linux/io.h>
#include <asm/irq.h>
#include <linux/irq.h>
#include <linux/fs.h>
#include <asm/arch/regs-gpio.h>
#include <linux/interrupt.h>
#include <linux/poll.h>

static struct class *key_class;     //创建类
static struct class_device *key_class_devs;   //创建类对应的设备
static struct timer_list keys_timer;

struct pin_desc{
    unsigned int pin;
    unsigned int key_val;
};
struct pin_desc pins_desc[4] = {
    {S3C2410_GPF0,0X01},
    {S3C2410_GPF2,0X02},
    {S3C2410_GPG3,0X03},
    {S3C2410_GPG11,0X04},
};

struct pin_desc *pin_timer;　　　　//在按键中断里保存按下按键的信息
unsigned char keyvals=0;

static volatile int ev_press = 0;
static DECLARE_WAIT_QUEUE_HEAD(button_waitq);

static struct fasync_struct *key_async_queue;

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

static irqreturn_t keys_irq(int irq, void *dev_id)
{
    pin_timer = (struct pin_desc *)dev_id;
    mod_timer(&keys_timer, jiffies+HZ/100 );　　//jiffies是个全局变量，每10ms累加一次，这里是10ms产生一次中断
    return IRQ_HANDLED;
}

int key_open(struct inode *inode, struct file *fp)
{
    /*获取信号量*/
    if( fp->f_flags & O_NONBLOCK )
    {
        if(down_trylock(&canopen))
            return -EBUSY;
    }
    else
    {
        down(&canopen);
    }
    request_irq( IRQ_EINT0, keys_irq, IRQT_BOTHEDGE, "key2", &pins_desc[0]);
    request_irq( IRQ_EINT2, keys_irq, IRQT_BOTHEDGE, "key3", &pins_desc[1]);
    request_irq( IRQ_EINT11, keys_irq, IRQT_BOTHEDGE, "key4", &pins_desc[2]);
    request_irq( IRQ_EINT19, keys_irq, IRQT_BOTHEDGE, "key5", &pins_desc[3]);
    return 0;
}

ssize_t key_read(struct file *fp, char __user *buff, size_t count, loff_t *offp){

    if(fp->f_flags & O_NONBLOCK )
    {
        if(!ev_press)
            return -EAGAIN;
    }
    else
    {
        wait_event_interruptible(button_waitq,ev_press);
    }
    if(count != 1)
    {
        return -EINVAL;
    }

    copy_to_user(buff,&keyvals,1);
    ev_press = 0;
    return 0;
}

ssize_t key_write(struct file *fp, const char __user *buf, size_t count, loff_t *ppos){
}

int key_close(struct inode *inode, struct file *file)
{
    free_irq(IRQ_EINT0,&pins_desc[0]);
    free_irq(IRQ_EINT2,&pins_desc[1]);
    free_irq(IRQ_EINT11,&pins_desc[2]);
    free_irq(IRQ_EINT19,&pins_desc[3]);
    up(&canopen);
}

static unsigned int key_poll(struct file *file, struct poll_table_struct *wait)
{
    unsigned int mask = 0;
    poll_wait(file, &button_waitq,wait);
    if(ev_press)
        mask |= POLLIN|POLLRDNORM;
    return mask;
}

static int key_fsync (int fd, struct file *filp, int on)
{
    printk("ok\n");
    return fasync_helper (fd, filp, on, &key_async_queue);
}

struct file_operations led_fops={
    .owner = THIS_MODULE,
    .open = key_open,
    .write  = key_write,
    .read   = key_read,
    .release = key_close,
    .poll = key_poll,
    .fasync = key_fsync,
};

static void keys_timer_fun(unsigned long t)
{
    struct pin_desc *pindesc = (struct pin_desc *)pin_timer;
    unsigned int pinval;
    if( !pindesc )
        return ;
    pinval = s3c2410_gpio_getpin(pindesc->pin);
    if(pinval)
    {
        keyvals = pindesc->key_val|0x80;

    }
    else
    {
        keyvals = pindesc->key_val;
    }
    ev_press = 1;
    wake_up_interruptible(&button_waitq);

    kill_fasync (&key_async_queue, SIGIO, POLL_IN);
    return ;
}

int major;
static int key_init(void)
{
    major = register_chrdev( 0,"key_drv", &led_fops );
    key_class = class_create(THIS_MODULE,"key_class");
    key_class_devs = class_device_create(key_class,NULL,MKDEV(major,0),NULL,"my_keys");

    init_timer(&keys_timer);
    keys_timer.function = keys_timer_fun;    /*定时器中断函数*/
    keys_timer.expires = 0;
    add_timer(&keys_timer);
    printk("key install Module\n");
    return 0;
}

static void key_exit(void)
{
    unregister_chrdev( major, "key_drv" );
    class_device_unregister(key_class_devs);
    class_destroy(key_class);
 　　del_timer(&keys_timer);　　　　//删除定时器   　printk("key Module exit\n");
}

module_init(key_init);
module_exit(key_exit);
MODULE_LICENSE("GPL");

测试应用程序：

#include <stdio.h>
#include <signal.h>
#include <fcntl.h>
#include <unistd.h>
int fd;
static char key_val;
int main( int argc, char **argv )
{
    int oflags;
    fd = open("/dev/my_keys",O_RDWR);/* O_NONBLOCK为非阻塞*/
    if(fd<0)
    {
        printf("open failed\n");
        return 0;
    }
    while(1)
    {
        read(fd,&key_val,1);
        printf("key_val:%d\n",key_val);
    }
    return 0;
}

sd