S5PV210 按鍵驅動源碼、應用程序解析（重點：中斷、休眠喚醒、定時器）

按鍵驅動是最簡單的功能，一旦使用linux來做就需要做很多功課。anyway，邏輯層還是前年不變的。先貼上驅動層代碼。

 

/*
 * linux/drivers/char/mini210_buttons.c
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/delay.h>
#include <linux/sched.h>
#include <linux/poll.h>
#include <linux/irq.h>
#include <asm/irq.h>
#include <asm/io.h>
#include <linux/interrupt.h>
#include <asm/uaccess.h>
#include <mach/hardware.h>
#include <linux/platform_device.h>
#include <linux/cdev.h>
#include <linux/miscdevice.h>

#include <mach/map.h>
#include <mach/gpio.h>
#include <mach/regs-clock.h>
#include <mach/regs-gpio.h>

#define DEVICE_NAME		"buttons"

struct button_desc {
	int gpio;
	int number;
	char *name;	
	struct timer_list timer;
};

static struct button_desc buttons[] = {
	{ S5PV210_GPH2(0), 0, "KEY0" },
	{ S5PV210_GPH2(1), 1, "KEY1" },
	{ S5PV210_GPH2(2), 2, "KEY2" },
	{ S5PV210_GPH2(3), 3, "KEY3" },
	{ S5PV210_GPH3(0), 4, "KEY4" },
	{ S5PV210_GPH3(1), 5, "KEY5" },
	{ S5PV210_GPH3(2), 6, "KEY6" },
	{ S5PV210_GPH3(3), 7, "KEY7" },
};

static volatile char key_values[] = {
	'0', '0', '0', '0', '0', '0', '0', '0'
};

static DECLARE_WAIT_QUEUE_HEAD(button_waitq);

static volatile int ev_press = 0;

static void mini210_buttons_timer(unsigned long _data)
{
	struct button_desc *bdata = (struct button_desc *)_data;
	int down;
	int number;
	unsigned tmp;

	tmp = gpio_get_value(bdata->gpio);

	/* active low */
	down = !tmp;
	printk("KEY %d: %08x\n", bdata->number, down);

	number = bdata->number;
	if (down != (key_values[number] & 1)) {
		key_values[number] = '0' + down;

		ev_press = 1;
		wake_up_interruptible(&button_waitq);
	}
}

static irqreturn_t button_interrupt(int irq, void *dev_id)
{
	struct button_desc *bdata = (struct button_desc *)dev_id;

	mod_timer(&bdata->timer, jiffies + msecs_to_jiffies(40));

	return IRQ_HANDLED;
}

static int mini210_buttons_open(struct inode *inode, struct file *file)
{
	int irq;
	int i;
	int err = 0;

	for (i = 0; i < ARRAY_SIZE(buttons); i++) {
		if (!buttons[i].gpio)
			continue;

		setup_timer(&buttons[i].timer, mini210_buttons_timer,
				(unsigned long)&buttons[i]);

		irq = gpio_to_irq(buttons[i].gpio);
		err = request_irq(irq, button_interrupt, IRQ_TYPE_EDGE_BOTH, 
				buttons[i].name, (void *)&buttons[i]);
		if (err)
			break;
	}

	if (err) {
		i--;
		for (; i >= 0; i--) {
			if (!buttons[i].gpio)
				continue;

			irq = gpio_to_irq(buttons[i].gpio);
			disable_irq(irq);
			free_irq(irq, (void *)&buttons[i]);

			del_timer_sync(&buttons[i].timer);
		}

		return -EBUSY;
	}

	ev_press = 1;
	return 0;
}

static int mini210_buttons_close(struct inode *inode, struct file *file)
{
	int irq, i;

	for (i = 0; i < ARRAY_SIZE(buttons); i++) {
		if (!buttons[i].gpio)
			continue;

		irq = gpio_to_irq(buttons[i].gpio);
		free_irq(irq, (void *)&buttons[i]);

		del_timer_sync(&buttons[i].timer);
	}

	return 0;
}

static int mini210_buttons_read(struct file *filp, char __user *buff,
		size_t count, loff_t *offp)
{
	unsigned long err;

	if (!ev_press) {
		if (filp->f_flags & O_NONBLOCK)
			return -EAGAIN;
		else
			wait_event_interruptible(button_waitq, ev_press);
	}

	ev_press = 0;

	err = copy_to_user((void *)buff, (const void *)(&key_values),
			min(sizeof(key_values), count));

	return err ? -EFAULT : min(sizeof(key_values), count);
}

static unsigned int mini210_buttons_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 struct file_operations dev_fops = {
	.owner		= THIS_MODULE,
	.open		= mini210_buttons_open,
	.release	= mini210_buttons_close, 
	.read		= mini210_buttons_read,
	.poll		= mini210_buttons_poll,
};

static struct miscdevice misc = {
	.minor		= MISC_DYNAMIC_MINOR,
	.name		= DEVICE_NAME,
	.fops		= &dev_fops,
};

static int __init button_dev_init(void)
{
	int ret;

	ret = misc_register(&misc);

	printk(DEVICE_NAME"\tinitialized\n");

	return ret;
}

static void __exit button_dev_exit(void)
{
	misc_deregister(&misc);
}

module_init(button_dev_init);
module_exit(button_dev_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("FriendlyARM Inc.");

非常經典的misc類驅動框架，驅動init用misc_register，exit用misc_deregister，太雞兒簡單了！

接下來應用層

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/select.h>
#include <sys/time.h>
#include <errno.h>

int main(void)
{
	int buttons_fd;
	char buttons[8] = {'0', '0', '0', '0', '0', '0', '0', '0'};

	buttons_fd = open("/dev/buttons", 0);
	if (buttons_fd < 0) {
		perror("open device buttons");
		exit(1);
	}

	for (;;) {
		char current_buttons[8];
		int count_of_changed_key;
		int i;
		if (read(buttons_fd, current_buttons, sizeof current_buttons) != sizeof current_buttons) {
			perror("read buttons:");
			exit(1);
		}

		for (i = 0, count_of_changed_key = 0; i < sizeof buttons / sizeof buttons[0]; i++) {
			if (buttons[i] != current_buttons[i]) {
				buttons[i] = current_buttons[i];
				printf("%skey %d is %s", count_of_changed_key? ", ": "", i+1, buttons[i] == '0' ? "up" : "down");
				count_of_changed_key++;
			}
		}
		if (count_of_changed_key) {
			printf("\n");
		}
		
		
	}

	close(buttons_fd);
	return 0;
}

應用層很簡單，無線循環中查詢值變化

A核心邏輯

加載ko，打開應用，應用open後read，然後進入休眠。之後按下按鈕，觸發中斷，中斷開啓定時器，定時器時間到後進入服務函數，此目的是防抖，在函數內讀取電平保存到arry中，喚醒應用層，應用層read值，打印到顯示器。

B難點

1.休眠機制

運行buttons應用程序，顯示狀態是S休眠狀態，可源碼裏是無限循環。休眠的目的很簡單：減少資源消耗。驅動進入休眠是驅動層read裏面的：

 wait_event_interruptible(button_waitq, ev_press);

 他的作用是調用read的時候檢查ev_press值，如果是0那麼就休眠了。

喚醒來自定時器服務函數

wake_up_interruptible(&button_waitq);

 喚醒之後應用read有效值，之後迅速重新睡眠，非常高效~

2.中斷

中斷是linux非常基礎也是重要的功能

獲取中斷號：

gpio_to_irq(buttons[i].gpio);

 申請中斷：

request_irq(irq, button_interrupt, IRQ_TYPE_EDGE_BOTH, buttons[i].name, (void *)&buttons[i]);

 中斷服務函數是button_interrupt

釋放中斷：

free_irq(irq, (void *)&buttons[i]);

3.定時器

定時器的作用是消抖 

建立定時器

setup_timer(&buttons[i].timer, mini210_buttons_timer,
                (unsigned long)&buttons[i]);

 設置消抖時間

mod_timer(&bdata->timer, jiffies + msecs_to_jiffies(40));

 C疑問點

1.IO沒有初始化，函數內找不到

static int __init button_dev_init(void)
{
	int ret;

	ret = misc_register(&misc);

	printk(DEVICE_NAME"\tinitialized\n");

	return ret;
}

2.timer是野指針,不需要申請嗎？

struct button_desc {
	int gpio;
	int number;
	char *name;	
	struct timer_list timer;
};

static struct button_desc buttons[] = {
	{ S5PV210_GPH2(0), 0, "KEY0" },
	{ S5PV210_GPH2(1), 1, "KEY1" },
	{ S5PV210_GPH2(2), 2, "KEY2" },
	{ S5PV210_GPH2(3), 3, "KEY3" },
	{ S5PV210_GPH3(0), 4, "KEY4" },
	{ S5PV210_GPH3(1), 5, "KEY5" },
	{ S5PV210_GPH3(2), 6, "KEY6" },
	{ S5PV210_GPH3(3), 7, "KEY7" },
};

3.poll未使用

static unsigned int mini210_buttons_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;
}

基本邏輯：應用層發起poll()進入休眠，按下按鍵進入irq觸發wake_up_interruptible喚醒。應用開始read值，打印至顯示器，重新poll進入休眠。與原文操作方法相比，poll取代了wait_event_interruptible。