Linux驅動之定時器在按鍵去抖中的應用
阿新 • • 發佈：2018-08-16
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機械按鍵在按下的過程中會出現抖動的情況，如下圖，這樣就會導致本來按下一次按鍵的過程會出現多次中斷，導致判斷出錯。在按鍵驅動程序中我們可以這麽做：
在按鍵驅動程序中我們可以這麽做來取消按鍵抖動的影響：當出現一個按鍵中斷後不會馬上去處理它，而是延時一個抖動時間（一般10ms），如果在這個時間內再次出現中斷那麽再次延時10ms。這樣循環，一直到在這個10ms內只有一個按鍵中斷，那麽就認為這次是真的按鍵值，然後在定時器處理函數裏處理它。上述過程可以利用內核的定時器來實現。
定時器二要素：定時時間、定時時間到後做什麽事情。根據這兩個要素來編寫程序，直接在sixth_drv.c的驅動程序上更改直接看到代碼：
1、定時器的創建，先建立一個定時器結構
static struct timer_list buttons_timer;//定義一個定時器
2、在模塊裝載時初始化定時器
static int sixth_drv_init(void) { /*增加一個定時器用於處理按鍵抖動*/ init_timer(&buttons_timer); buttons_timer.expires = 0;//定時器的定時時間 // buttons_timer->data = (unsigned long) cs; buttons_timer.function = buttons_timeout;//定時時間到後的處理函數add_timer(&buttons_timer);//將定義的定時器放入定時器鏈表 sixthmajor = register_chrdev(0, "buttons", &sixth_drv_ops);//註冊驅動程序 if(sixthmajor < 0) printk("failes 1 buttons_drv register\n"); sixth_drv_class = class_create(THIS_MODULE, "buttons");//創建類 if(sixth_drv_class < 0) printk("failes 2 buttons_drv register\n"); sixth_drv_class_dev = class_device_create(sixth_drv_class, NULL, MKDEV(sixthmajor,0), NULL,"buttons");//創建設備節點 if(sixth_drv_class_dev < 0) printk("failes 3 buttons_drv register\n"); gpfcon = ioremap(0x56000050, 16);//重映射 gpfdat = gpfcon + 1; gpgcon = ioremap(0x56000060, 16);//重映射 gpgdat = gpgcon + 1; printk("register buttons_drv\n"); return 0; }
3、編寫定時器處理函數
static void buttons_timeout(unsigned long data) { unsigned int pin_val; static long cnt=0; //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) //按鍵松開 key_val = 0x80 | pin_des->key_val; else key_val = pin_des->key_val; wake_up_interruptible(&button_waitq); /* 喚醒休眠的進程 */ ev_press = 1; kill_fasync(&sixth_fasync, SIGIO, POLL_IN);//發生信號給進程 } }
4、當在卸載驅動時將定時器刪除；在中斷處理程序中直接改變定時器的超時時間，並記錄下是哪個按鍵按下的即可，其他處理都在定時器超時函數中。直接看到完整代碼：
#include <linux/module.h> #include <linux/kernel.h> #include <linux/fs.h> #include <linux/init.h> #include <asm/io.h> //含有iomap函數iounmap函數 #include <asm/uaccess.h>//含有copy_from_user函數 #include <linux/device.h>//含有類相關的處理函數 #include <asm/arch/regs-gpio.h>//含有S3C2410_GPF0等相關的 #include <linux/irq.h> //含有IRQ_HANDLED\IRQ_TYPE_EDGE_RISING #include <asm-arm/irq.h> //含有IRQT_BOTHEDGE觸發類型 #include <linux/interrupt.h> //含有request_irq、free_irq函數 #include <linux/poll.h> #include <asm-generic/errno-base.h> //含有各種錯誤返回值 //#include <asm-arm\arch-s3c2410\irqs.h> static struct class *sixth_drv_class;//類 static struct class_device *sixth_drv_class_dev;//類下面的設備 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[4] = { {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);//註冊一個等待隊列button_waitq static atomic_t open_flag = ATOMIC_INIT(1); //定義原子變量open_flag 並初始化為1 static DECLARE_MUTEX(button_lock); //定義互斥鎖 static struct timer_list buttons_timer;//定義一個定時器 /* *0x01、0x02、0x03、0x04表示按鍵被按下 */ /* *0x81、0x82、0x83、0x84表示按鍵被松開 */ /* *利用dev_id的值為pins_desc來判斷是哪一個按鍵被按下或松開 */ static irqreturn_t buttons_irq(int irq, void *dev_id) { pin_des = (struct pin_desc *)dev_id;//取得哪個按鍵被按下的狀態 mod_timer(&buttons_timer, jiffies+HZ/100);//10ms之後調用定時器處理函數 return IRQ_HANDLED; } static int sixth_drv_open (struct inode * inode, struct file * file) { int ret; // if(atomic_dec_and_test(&open_flag)==0)//自檢後是否為0,不為0說明已經被人調用 // { // atomic_inc(&open_flag);//原子變量+1 // return -EBUSY; // } if(file->f_flags & O_NONBLOCK)//非阻塞方式 { if(down_trylock(&button_lock))//獲取信號量失敗則返回 return -EBUSY; } else down(&button_lock);//獲得信號量 ret = request_irq(IRQ_EINT0, buttons_irq, IRQT_BOTHEDGE, "s1", (void * )&pins_desc[0]); if(ret) { printk("open failed 1\n"); return -1; } ret = request_irq(IRQ_EINT2, buttons_irq, IRQT_BOTHEDGE, "s2", (void * )& pins_desc[1]); if(ret) { printk("open failed 2\n"); return -1; } ret = request_irq(IRQ_EINT11, buttons_irq, IRQT_BOTHEDGE, "s3", (void * )&pins_desc[2]); if(ret) { printk("open failed 3\n"); return -1; } ret = request_irq(IRQ_EINT19, buttons_irq, IRQT_BOTHEDGE, "s4", (void * )&pins_desc[3]); if(ret) { printk("open failed 4\n"); return -1; } return 0; } static int sixth_drv_close(struct inode * inode, struct file * file) { // atomic_inc(&open_flag);//原子變量+1 up(&button_lock);//釋放信號量 free_irq(IRQ_EINT0 ,(void * )&pins_desc[0]); free_irq(IRQ_EINT2 ,(void * )& pins_desc[1]); free_irq(IRQ_EINT11 ,(void * )&pins_desc[2]); free_irq(IRQ_EINT19 ,(void * )&pins_desc[3]); return 0; } static ssize_t sixth_drv_read(struct file * file, char __user * userbuf, size_t count, loff_t * off) { int ret; if(count != 1) { printk("read error\n"); return -1; } if(file->f_flags & O_NONBLOCK)//非阻塞方式 { if(!ev_press)//判斷是否有按鍵按下，如果沒有直接返回 { key_val = 0; ret = copy_to_user(userbuf, &key_val, 1); return -EBUSY; } } else//如果沒有按鍵動作，直接進入休眠 wait_event_interruptible(button_waitq, ev_press);//將當前進程放入等待隊列button_waitq中 ret = copy_to_user(userbuf, &key_val, 1); ev_press = 0;//按鍵已經處理可以繼續睡眠 if(ret) { printk("copy error\n"); return -1; } return 1; } static unsigned int sixth_drv_poll(struct file *file, poll_table *wait) { unsigned int ret = 0; poll_wait(file, &button_waitq, wait);//將當前進程放到button_waitq列表 if(ev_press) ret |=POLLIN;//說明有數據被取到了 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 < 0) return err; return 0; } 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=0; //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) //按鍵松開 key_val = 0x80 | pin_des->key_val; else key_val = pin_des->key_val; wake_up_interruptible(&button_waitq); /* 喚醒休眠的進程 */ ev_press = 1; kill_fasync(&sixth_fasync, SIGIO, POLL_IN);//發生信號給進程 } } static int sixth_drv_init(void) { /*增加一個定時器用於處理按鍵抖動*/ init_timer(&buttons_timer); buttons_timer.expires = 0;//定時器的定時時間 // buttons_timer->data = (unsigned long) cs; buttons_timer.function = buttons_timeout;//定時時間到後的處理函數 add_timer(&buttons_timer);//將定義的定時器放入定時器鏈表 sixthmajor = register_chrdev(0, "buttons", &sixth_drv_ops);//註冊驅動程序 if(sixthmajor < 0) printk("failes 1 buttons_drv register\n"); sixth_drv_class = class_create(THIS_MODULE, "buttons");//創建類 if(sixth_drv_class < 0) printk("failes 2 buttons_drv register\n"); sixth_drv_class_dev = class_device_create(sixth_drv_class, NULL, MKDEV(sixthmajor,0), NULL,"buttons");//創建設備節點 if(sixth_drv_class_dev < 0) printk("failes 3 buttons_drv register\n"); gpfcon = ioremap(0x56000050, 16);//重映射 gpfdat = gpfcon + 1; gpgcon = ioremap(0x56000060, 16);//重映射 gpgdat = gpgcon + 1; printk("register buttons_drv\n"); return 0; } 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、測試代碼還是沿用sisth_test.c。將驅動程序和測試程序編譯後的文件放入網絡文件系統，測試發現不再出現抖動情況。具體過程參考Linux驅動之按鍵驅動編寫（中斷方式）
Linux驅動之定時器在按鍵去抖中的應用