學過單片機的都知道,按鍵可能會出現抖動現象。linux也一樣。
如下,出現兩次按下的輸出值
按鍵由於他的物理特性,可能會在按鍵鬆開時產生多次脈衝,每次脈衝都可能產生中斷。關鍵是消除多次讀取脈衝,只讀一次。引入定時器,每隔多少時間之後讀取(錯過抖動時序)。
一.內核定時器
參考《linux設備驅動程序p196》
如果我們需要在將來的某個時間點調度執行某個動作,同時在該時間點到達之前不會阻塞當前進程,則可以使用內核定時器。
頭文件和實現文件:<linux/timer.h> <kernel/timer.c>
定時器API
struct timer_list {
/*....*/
unsigned long expires;
void (*function)(unsigned long);
unsigned long data;
/*....*/
};
struct timer_list TIMER_INITIALIZER(_function,_expires,_data); //定義結構體變量
void init_timer(struct timer_list *timer); //初始化
void add_timer(struct timer_list *timer); //
int del_timer(struct timer_list *timer);
int mod_timer(struct timer_list *timer,unsigned long expires); //更新某個定時器的到期時間
全局變量jiffies_64就和HZ有關,它是一個64位整型變量,記錄了系統啓動以來時鐘中斷的個數(也就是tick數)。我們知道HZ是每秒鐘產生的時鐘中斷的個數,那麼jiffies_64每秒鐘就增加HZ大小的值,例如,如果HZ=250,那jiffies_64在一秒後會變爲jiffies_64+250,也就是精度爲1000/HZ毫秒。在timer_list定時器中設置到期時間時,我們會用 (jiffies + 5 * HZ) 來表示5秒後到期就是這個道理。
二.修改代碼支持定時器防抖
以前在中斷處理函數裏,我們做的是讀取按鍵值,異步通知。現在把這些代碼搬過去定時器的function中,實現按下按鍵後隔10ms後再讀取按鍵值。
步驟:
1.定義定時器結構體
2.初始化
3.把中斷處理函數的代碼搬過去定時器fuction中並修改,修改中斷處理函數
jiffies參考:Linux中的jiffies介紹
在中斷處理函數裏使用mod_timer,當發生中斷時,會更新超時時間,比如當前滴答時鐘爲100,設置110後就會去調用定時器的fuction函數。
4.釋放定時器
del_timer(&mybuttons_timer);
三.代碼
#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>
#include <linux/timer.h>
static struct class *seconddrv_buttons_class;
static struct class_device *seconddrv_buttons_class_dev;
static struct fasync_struct *button_async;
volatile unsigned long *gpfcon;
volatile unsigned long *gpfdat;
volatile unsigned long *gpgcon;
volatile unsigned long *gpgdat;
struct timer_list mybuttons_timer;
static DECLARE_WAIT_QUEUE_HEAD(button_waitq); //定義並初始化等待隊列
//static int canopen=1;
static DECLARE_MUTEX(button_lock); //定義互斥鎖
/* 中斷事件標誌, 中斷服務程序將它置1,third_drv_read將它清0 */
static volatile int ev_press = 0;
struct pin_desc{
unsigned int pin;
unsigned int key_val;
};
/* 鍵值: 按下時, 0x01, 0x02, 0x03, 0x04 */
/* 鍵值: 鬆開時, 0x81, 0x82, 0x83, 0x84 */
struct pin_desc pins_desc[4] = {
{S3C2410_GPF0, 0x01},
{S3C2410_GPF2, 0x02},
{S3C2410_GPG3, 0x03},
{S3C2410_GPG11, 0x04},
};
struct pin_desc *irq_dev;
static unsigned char key_val;
static irqreturn_t mybuttons_irq(int irq, void *dev_id)
{
irq_dev=(struct pin_desc *)dev_id;
mod_timer(&mybuttons_timer,jiffies+HZ/100);//jiffies是當前的tick,HZ代表1s,HZ/100=10ms.jiffies會++到jiffies+10ms後產生定時器中斷
return IRQ_RETVAL(IRQ_HANDLED);
}
static int seconddrv_buttons_open(struct inode *inode, struct file *file)
{
/*獲取信號量,只有第一個應用程序纔可以獲得,其餘應用程序會在這裏陷入休眠*/
down(&button_lock);
/*配置GPF0,2爲輸入引腳,中斷號參考arch\arm\plat-s3c24xx\Irq.c的s3c24xx_init_irq*/
/*配置GPG3,11爲輸入引腳*/
request_irq(IRQ_EINT0, mybuttons_irq, IRQT_BOTHEDGE, "S1", &pins_desc[0]);
request_irq(IRQ_EINT2, mybuttons_irq, IRQT_BOTHEDGE, "S2", &pins_desc[1]);
request_irq(IRQ_EINT11, mybuttons_irq, IRQT_BOTHEDGE, "S3", &pins_desc[2]);
request_irq(IRQ_EINT19, mybuttons_irq, IRQT_BOTHEDGE, "S4", &pins_desc[3]);
//printk("seconddrv_open\n");
return 0;
}
ssize_t seconddrv_buttons_read(struct file *file, char __user *buf,size_t size, loff_t *ppos)
{
if (size != 1)
return -EINVAL;
// 沒有按鍵按下時,休眠
//wait_event_interruptible(button_waitq, ev_press);
//按鍵按下時
copy_to_user(buf, &key_val,1);
//ev_press = 0;
return 1;
}
static int seconddrv_buttons_close(struct inode * inode, struct file * file)
{
/*應用程序用完後,釋放信號量*/
up(&button_lock);
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]);
return 0;
}
static unsigned int secondddrv_butttons_poll(struct file *file, struct poll_table_struct *wait)
{
unsigned int mask = 0;
poll_wait(file, &button_waitq, wait); // 不會立即休眠
if (ev_press) //ev_press 不爲 0 時,poll 休眠直到time_out後break循環體 ,爲1時,break
mask |= POLLIN | POLLRDNORM;
return mask;
}
static int secondddrv_butttons_fasync(int fd, struct file *filp, int on)
{
printk("secondddrv_butttons_fasync\n");
return fasync_helper (fd, filp, on, &button_async);
}
static struct file_operations seconddrv_buttons_fops = {
.owner = THIS_MODULE, /* 這是一個宏,推向編譯模塊時自動創建的__this_module變量 */
.open = seconddrv_buttons_open,
.read = seconddrv_buttons_read,
.release= seconddrv_buttons_close,
.poll = secondddrv_butttons_poll,
.fasync = secondddrv_butttons_fasync,
};
static void mybuttons_timerfun(unsigned long p)
{
unsigned int pinval;
struct pin_desc *pindesc =irq_dev;
if(!pindesc)
return;
pinval = s3c2410_gpio_getpin(pindesc->pin); //內核提供的讀取引腳值的函數
if(pinval) // 1爲鬆開
{
key_val =0x80 | pindesc->key_val;
}
else
{
key_val =pindesc->key_val;
}
//ev_press = 1; /* 中斷標誌位=1,表示中斷髮生了 */
//wake_up_interruptible(&button_waitq); /* 喚醒休眠的進程 */\
kill_fasync (&button_async, SIGIO, POLL_IN);
}
int major;
int seconddrv_buttons_init(void)
{
init_timer(&mybuttons_timer); //初始化定時器
//mybuttons_timer.data = (unsigned long) SCpnt; //function的傳參,不用可省略
//mybuttons_timer.expires = jiffies + 100*HZ; /* 超時時間,放在中斷處理函數使用,沒有設置默認=0,即fuction會立即執行 */
mybuttons_timer.function = mybuttons_timerfun;
add_timer(&mybuttons_timer);
major = register_chrdev(0,"seconddrv",&seconddrv_buttons_fops);
seconddrv_buttons_class = class_create(THIS_MODULE,"buttons");
seconddrv_buttons_class_dev = class_device_create(seconddrv_buttons_class,NULL,MKDEV(major,0),NULL,"mybuttons");
gpfcon = (volatile unsigned long *)ioremap(0x56000050,16);
gpfdat = gpfcon + 1;
gpgcon = (volatile unsigned long *)ioremap(0x56000060,16);
gpgdat = gpgcon +1;
return 0;
}
void seconddrv_buttons_exit(void)
{
unregister_chrdev(major,"seconddrv");
class_destroy(seconddrv_buttons_class);
class_device_unregister(seconddrv_buttons_class_dev);
iounmap(gpfcon);
iounmap(gpgcon);
del_timer(&mybuttons_timer);
return 0;
}
module_init(seconddrv_buttons_init);
module_exit(seconddrv_buttons_exit);
MODULE_LICENSE("GPL");
測試代碼:
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <poll.h>
#include <signal.h>
#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>
/* fifthdrvtest
*/
int fd;
void my_signal_fun(int signum)
{
unsigned char key_val;
read(fd, &key_val, 1);
printf("key_val: 0x%x\n", key_val);
}
int main(int argc, char **argv)
{
unsigned char key_val;
int ret;
int Oflags;
signal(SIGIO, my_signal_fun);
fd = open("/dev/mybuttons", O_RDWR);
if (fd < 0)
{
printf("can't open!\n");
return -1;
}
fcntl(fd, F_SETOWN, getpid());
Oflags = fcntl(fd, F_GETFL);
fcntl(fd, F_SETFL, Oflags | FASYNC);
while (1)
{
sleep(1000);
}
return 0;
}
測試結果: