驱动程序之_1_字符设备_7_非阻塞

阻塞操作
是指在执行设备操作时若不能获得资源则挂起进程，直到满足可操作的条件后再进行操作。
被挂起的进程进入休眠状态，被从调度器的运行队列移走，直到等待的条件被满足。

非阻塞操作
进程在不能进行设备操作时并不挂起，它或者放弃，或者不停地查询，直至可以进行操作为止。

驱动程序中：
如果是以非阻塞方式打开文件，在读函数中，判断是否按下按键，若有按键则返回键值，否则直接退回应用程序；而如果以阻塞方式打开（前面关于按键中断的文章就是这种情况），则进程会进入休眠，等待按键事件触发

应用程序中：
1、以非阻塞方式打开设备文件

fd = open("/dev/key_irq_drv",O_RDWR | O_NONBLOCK);

2、休眠时间设定为2s，2s秒循环一次代码
3、一次循环只进行一次读操作，所以即使2s内按下多次按键，也只会按2s的周期返回一次键值

附上驱动程序和测试用的应用程序代码

驱动程序

#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/device.h>
#include <linux/irq.h>

static struct class *my_irq_class;
static struct class_device *my_irq_class_device;

static unsigned char key_val;

static DECLARE_MUTEX(button_lock);

static DECLARE_WAIT_QUEUE_HEAD(button_waitq);

static volatile int ev_press = 0;

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

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

static irqreturn_t buttons_irq(int irq,void *dev_id)
{
	struct pin_desc *pindesc = (struct pin_desc *)dev_id;
	unsigned int pinval;
	
	pinval = s3c2410_gpio_getpin(pindesc->pin);
	if(pinval)	//松开
	{
		key_val = 0x80 | pindesc->key_val;
	}
	else
	{
		key_val = pindesc->key_val;
	}
	
	ev_press = 1;
	wake_up_interruptible(&button_waitq);
	
	return IRQ_HANDLED;
}

static int my_irq_drv_open(struct inode *inode, struct file *file)
{
	if(file->f_flags & O_NONBLOCK)
	{
		if(down_trylock(&button_lock))
			return -EBUSY;
	}
	else
	{
		down(&button_lock);
	}
	
	request_irq(IRQ_EINT0,buttons_irq,IRQT_BOTHEDGE,"S2",&key_pins_desc[0]);
	request_irq(IRQ_EINT2,buttons_irq,IRQT_BOTHEDGE,"S3",&key_pins_desc[1]);
	request_irq(IRQ_EINT11,buttons_irq,IRQT_BOTHEDGE,"S4",&key_pins_desc[2]);
	request_irq(IRQ_EINT19,buttons_irq,IRQT_BOTHEDGE,"S5",&key_pins_desc[3]);	

	return 0;
}

int my_irq_drv_close(struct inode *inode,struct file *file)
{
	up(&button_lock);
 
	free_irq(IRQ_EINT0,&key_pins_desc[0]);
	free_irq(IRQ_EINT2,&key_pins_desc[1]);
	free_irq(IRQ_EINT11,&key_pins_desc[2]);
	free_irq(IRQ_EINT19,&key_pins_desc[3]);
	
	return 0;
}


ssize_t my_irq_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
	{
		wait_event_interruptible(button_waitq,ev_press);
	}

	ev_press = 0;
	
	copy_to_user(buf,&key_val,1);

	return 0;
}

static struct file_operations irq_drv_fops = {
	.owner = THIS_MODULE,
	.open = my_irq_drv_open,
	.read = my_irq_drv_read,
	.release = my_irq_drv_close,
};

static int major;

static int my_irq_drv_init(void)
{
	major = register_chrdev(0,"my_irq_drv",&irq_drv_fops);
	my_irq_class = class_create(THIS_MODULE,"my_irq_drv");
	my_irq_class_device = class_device_create(my_irq_class,NULL,MKDEV(major,0),NULL,"key_irq_drv");

	return 0;
}

static void my_irq_drv_exit(void)
{
	unregister_chrdev(major,"my_irq_drv");
	class_device_unregister(my_irq_class_device);
	class_destroy(my_irq_class);
}

module_init(my_irq_drv_init);
module_exit(my_irq_drv_exit);
MODULE_LICENSE("GPL");

应用程序

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <poll.h>
#include <signal.h>
#include <unistd.h>
#include <fcntl.h>

int main(int argc,char *args[])
{

	unsigned char key_val;
	
	int fd;
	int ret;
	
	fd = open("/dev/key_irq_drv",O_RDWR | O_NONBLOCK);
	if(fd < 0)
	{
		printf("can't open\r\n");
		return 0;
	}
	printf("open successfully\r\n");


	while(1)
	{
		ret = read(fd,&key_val,1);
		printf("key_val : 0x%x , ret : %d\r\n",key_val,ret);
		sleep（2);
	}

	return 0;
}