Linux驱动学习笔记（7）

 字符设备驱动程序之定时器防抖动

之前的按键驱动程序，在连续按快点的时候会出现偶尔“失灵”的情况，一按一松并没有完全如所预料的那样执行，如果在现场应用中出现这种问题，可能会导致很严重的后果。之前写单片机程序的时候，按键的消抖是通过一个延时来判定（当检测到有按键按下的时候，延时一段时间，然后再次判断，如果有按键按下，就判定按键按下了）。
使用定时器的两要素：1，超时时间、2，处理函数。

#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 <asm/irq.h>
#include <asm/io.h>
#include <asm/arch/regs-gpio.h>
#include <asm/hardware.h>
#include <linux/poll.h>


static struct class *sixthdrv_class;
static struct class_device    *sixthdrv_class_dev;

volatile unsigned long *gpfcon;
volatile unsigned long *gpfdat;

volatile unsigned long *gpgcon;
volatile unsigned long *gpgdat;

static struct timer_list buttons_timer;     // 定义一个结构体 buttons_timer


static DECLARE_WAIT_QUEUE_HEAD(button_waitq);

/* 中断事件标志, 中断服务程序将它置1，sixth_drv_read将它清0 */
static volatile int ev_press = 0;

static struct fasync_struct *button_async;


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


/* 键值: 按下时, 0x01, 0x02, 0x03, 0x04 */
/* 键值: 松开时, 0x81, 0x82, 0x83, 0x84 */
static unsigned char key_val;

struct pin_desc pins_desc[4] = {
    {S3C2410_GPF0, 0x01},
    {S3C2410_GPF2, 0x02},
    {S3C2410_GPG3, 0x03},
    {S3C2410_GPG11, 0x04},
};

static struct pin_desc *irq_pd;

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

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

/*
  * 确定按键值
  */
static irqreturn_t buttons_irq(int irq, void *dev_id)
{
    /* 10ms后启动定时器 */
    irq_pd = (struct pin_desc *)dev_id;
    mod_timer(&buttons_timer, jiffies+HZ/100); // mod就是modify修改定时器超时间，jiffies是一个全局变量，jiffies每隔10ms就会产生一个系统时钟中断，超时时间为jiffies+HZ/100,HZ/100即为100ms.时间到调用处理函数buttons_timer_function（）;
    return IRQ_RETVAL(IRQ_HANDLED);
}

static int sixth_drv_open(struct inode *inode, struct file *file)
{
#if 0
    if (!atomic_dec_and_test(&canopen))
    {
        atomic_inc(&canopen);
        return -EBUSY;
    }
#endif

    if (file->f_flags & O_NONBLOCK)
    {
        if (down_trylock(&button_lock))
            return -EBUSY;
    }
    else
    {
        /* 获取信号量 */
        down(&button_lock);
    }

    /* 配置GPF0,2为输入引脚 */
    /* 配置GPG3,11为输入引脚 */
    request_irq(IRQ_EINT0, buttons_irq, IRQT_BOTHEDGE, "S2", &pins_desc[0]);
    request_irq(IRQ_EINT2, buttons_irq, IRQT_BOTHEDGE, "S3", &pins_desc[1]);
    request_irq(IRQ_EINT11, buttons_irq, IRQT_BOTHEDGE, "S4", &pins_desc[2]);
    request_irq(IRQ_EINT19, buttons_irq, IRQT_BOTHEDGE, "S5", &pins_desc[3]);

    return 0;
}

ssize_t sixth_drv_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
{
    if (size != 1)
        return -EINVAL;

    if (file->f_flags & O_NONBLOCK)
    {
        if (!ev_press)
            return -EAGAIN;
    }
    else
    {
        /* 如果没有按键动作, 休眠 */
        wait_event_interruptible(button_waitq, ev_press);
    }

    /* 如果有按键动作, 返回键值 */
    copy_to_user(buf, &key_val, 1);
    ev_press = 0;

    return 1;
}


int sixth_drv_close(struct inode *inode, struct file *file)
{
    //atomic_inc(&canopen);
    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(&button_lock);
    return 0;
}

static unsigned sixth_drv_poll(struct file *file, poll_table *wait)
{
    unsigned int mask = 0;
    poll_wait(file, &button_waitq, wait); // 不会立即休眠

    if (ev_press)
        mask |= POLLIN | POLLRDNORM;

    return mask;
}

static int sixth_drv_fasync (int fd, struct file *filp, int on)
{
    printk("driver: sixth_drv_fasync\n");
    return fasync_helper (fd, filp, on, &button_async);
}


static struct file_operations sencod_drv_fops = {
    .owner = THIS_MODULE, /* 这是一个宏，指向编译模块时自动创建的__this_module变量 */
    .open = sixth_drv_open,
    .read     =    sixth_drv_read,
    .release = sixth_drv_close,
    .poll = sixth_drv_poll,
    .fasync     = sixth_drv_fasync,
};


int major;

static void buttons_timer_function(unsigned long data)
{
    struct pin_desc * pindesc = irq_pd;
    unsigned int pinval;

    if (!pindesc)
        return;

    pinval = s3c2410_gpio_getpin(pindesc->pin);

    if (pinval)
    {
        /* 松开 */
        key_val = 0x80 | pindesc->key_val;
    }
    else
    {
        /* 按下 */
        key_val = pindesc->key_val;
    }

    ev_press = 1; /* 表示中断发生了 */
    wake_up_interruptible(&button_waitq); /* 唤醒休眠的进程 */

    kill_fasync (&button_async, SIGIO, POLL_IN);
}


static int sixth_drv_init(void)
{
    init_timer(&buttons_timer);             // 对timer进行初始化
    buttons_timer.function = buttons_timer_function;
    //buttons_timer.expires = 0;            // 超时时间不用（因为是在中断处理函数里面用的定时器）
    add_timer(&buttons_timer);

    major = register_chrdev(0, "sixth_drv", &sencod_drv_fops);

    sixthdrv_class = class_create(THIS_MODULE, "sixth_drv");

    sixthdrv_class_dev = class_device_create(sixthdrv_class, NULL, MKDEV(major, 0), NULL, "buttons"); /* /dev/buttons */

    gpfcon = (volatile unsigned long *)ioremap(0x56000050, 16);
    gpfdat = gpfcon + 1;

    gpgcon = (volatile unsigned long *)ioremap(0x56000060, 16);
    gpgdat = gpgcon + 1;

    return 0;
}

static void sixth_drv_exit(void)
{
    unregister_chrdev(major, "sixth_drv");
    class_device_unregister(sixthdrv_class_dev);
    class_destroy(sixthdrv_class);
    iounmap(gpfcon);
    iounmap(gpgcon);
    return 0;
}


module_init(sixth_drv_init);

module_exit(sixth_drv_exit);

MODULE_LICENSE("GPL");

测试程序可以用之前提供的。