S5PV210 按键驱动源码、应用程序解析（重点：中断、休眠唤醒、定时器）

按键驱动是最简单的功能，一旦使用linux来做就需要做很多功课。anyway，逻辑层还是前年不变的。先贴上驱动层代码。

 

/*
 * 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 
#include 
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#include 
#include 
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#include 
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#include 

#include 
#include 
#include 
#include 

#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.");

非常经典的misc类驱动框架，驱动init用misc_register，exit用misc_deregister，太鸡儿简单了！

接下来应用层

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

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;
}

应用层很简单，无线循环中查询值变化

A核心逻辑

加载ko，打开应用，应用open后read，然后进入休眠。之后按下按钮，触发中断，中断开启定时器，定时器时间到后进入服务函数，此目的是防抖，在函数内读取电平保存到arry中，唤醒应用层，应用层read值，打印到显示器。

B难点

1.休眠机制

运行buttons应用程序，显示状态是S休眠状态，可源码里是无限循环。休眠的目的很简单：减少资源消耗。驱动进入休眠是驱动层read里面的：

 wait_event_interruptible(button_waitq, ev_press);

 他的作用是调用read的时候检查ev_press值，如果是0那么就休眠了。

唤醒来自定时器服务函数

wake_up_interruptible(&button_waitq);

 唤醒之后应用read有效值，之后迅速重新睡眠，非常高效~

2.中断

中断是linux非常基础也是重要的功能

获取中断号：

gpio_to_irq(buttons[i].gpio);

 申请中断：

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

 中断服务函数是button_interrupt

释放中断：

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

3.定时器

定时器的作用是消抖 

建立定时器

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

 设置消抖时间

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

 C疑问点

1.IO没有初始化，函数内找不到

static int __init button_dev_init(void)
{
	int ret;

	ret = misc_register(&misc);

	printk(DEVICE_NAME"\tinitialized\n");

	return ret;
}

2.timer是野指针,不需要申请吗？

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;
}

基本逻辑：应用层发起poll()进入休眠，按下按键进入irq触发wake_up_interruptible唤醒。应用开始read值，打印至显示器，重新poll进入休眠。与原文操作方法相比，poll取代了wait_event_interruptible。