字符设备驱动程序——按键中断poll机制

编译环境
ubunt 16.04
arm-linux-gcc 4.3.2
linux-3.4.2
zj2440

poll的作用是把当前的文件指针挂到等待队列。

对于一个按键事件：
1、查询方法：在while(1)中不断循环调用read(fd, &key_val, 1)查询，不断去查询是否有事件发生，整个过程都是占用CPU资源，消耗CPU资源非常大。

2、中断方式：当有事件发生时，就去跳转到相应事件去处理，CPU占用时间少。若没有按键按下，则要一直处于休眠状态

3、poll方式:当有事件发生时，才去执行读read函数，按键事件没有按下时，返回超时错误信息，进程能够继续得到执行。

---

poll实现步骤：
1、在驱动函数file_operation结构体上添加一个.poll函数，然后在函数里执行poll_wait，这个函数用来判断硬件事件是否发生
2、测试程序需要调用ret = poll(fds, 1, 5000) 【超时时间为5s】，函数来获取事件发生信息。

#include <linux/module.h>
#include <linux/sched.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 <linux/device.h>
#include <mach/gpio.h>
#include <linux/interrupt.h>
#include <linux/poll.h>



static struct class *newdrv_class;

volatile unsigned long *gpfcon = NULL;
volatile unsigned long *gpfdat = NULL;
volatile unsigned long *gpgdat = NULL;
volatile unsigned long *gpgcon = NULL;

static DECLARE_WAIT_QUEUE_HEAD(button_waitq);

/* 中断事件标志, 中断服务程序将它置1，s3c24xx_buttons_read将它清0 */
static volatile int ev_press = 0;
static unsigned char key;

struct pin_desc{
	unsigned int pin;//引脚
	unsigned int key_val;//键值,按下01 02 03 04；松开81 82 83 84
};

struct pin_desc pins_desc[4]={
	{S3C2410_GPF(0), 0x01},
	{S3C2410_GPF(2), 0x02},
	{S3C2410_GPG(3), 0x03},
	{S3C2410_GPG(11), 0x04},
};

static int 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);//读引脚
	if(pinval)//1 松开
	{
		key=0x80|pindesc->key_val;
	}
	else//按下
		key=pindesc->key_val;
	
	  ev_press = 1;                           /* 表示中断发生了 */
	  wake_up_interruptible(&button_waitq);   /* 唤醒休眠的进程 */
	  
	return IRQ_RETVAL(IRQ_HANDLED);//接收到了中断信号,并处理，返回1
}

static int new_drv_open(struct inode *inode, struct file *file)
{
				/* 中断引脚			中断函数		触发方式（双边沿）									名称	   传入dev―id */
	request_irq(IRQ_EINT0,  buttons_irq, (IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING), "S2", &pins_desc[0]);
	request_irq(IRQ_EINT2,  buttons_irq, (IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING), "S3", &pins_desc[1]);
	request_irq(IRQ_EINT11, buttons_irq, (IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING), "S4", &pins_desc[2]);
	request_irq(IRQ_EINT19, buttons_irq, (IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING), "S5", &pins_desc[3]);
	return 0;
}

static ssize_t new_drv_read(struct file *file, const char __user *buf, size_t count, loff_t * ppos)
{
	if(count!=1)
		return -EINVAL;
	
	/*没有按键动作，ev_press=0,在此休眠,唤醒后往后执行*/
	wait_event_interruptible(button_waitq,ev_press);

	copy_to_user(buf, &key, 1);
	ev_press=0;
	return 1;
}

static int new_drv_close(struct inode *inode, struct file *file)
{
	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 int new_drv_poll(struct file *file,poll_table *wait)
{
	unsigned int mask=0;
	poll_wait(file,&button_waitq, wait);//进程挂入button_waitq队列，不会立即休眠
	if(ev_press)   //为1时退出休眠
		mask|=POLLIN|POLLRDNORM;
		/*mask=0时休眠，非0时唤醒*/
	return mask;
}


static struct file_operations new_drv_fops = {
    .owner  =THIS_MODULE,    /* 这是一个宏，推向编译模块时自动创建的__this_module变量 */
    .open   =new_drv_open,     
	.read   =new_drv_read,
	.release=new_drv_close,
	.poll   =new_drv_poll,
};

int major;
static int new_drv_init(void)
{
	major = register_chrdev(0, "newdrv", &new_drv_fops); // 注册, 自动分配并返回主设备号
		*/*在/sys/class/下创建类目录*/*
	newdrv_class = class_create(THIS_MODULE, "newdrv");
		*/*根据类目录，在驱动模块初始化函数中实现设备节点的自动创建/dev/newdrv*/*
	device_create(newdrv_class, NULL, MKDEV(major, 0), NULL, "newdrv"); 

	gpfcon = (volatile unsigned long *)ioremap(0x56000050, 16);
	gpfdat = gpfcon + 1;
	gpgcon = (volatile unsigned long *)ioremap(0x56000060, 16);
	gpgdat = gpgcon + 1;

	return 0;
}

static void new_drv_exit(void)
{
	unregister_chrdev(major, "newdrv"); // 卸载，删除
	device_destroy(newdrv_class,MKDEV(major, 0));
	class_destroy(newdrv_class);
	iounmap(gpfcon);
	iounmap(gpgcon);
}

module_init(new_drv_init);//入口函数
module_exit(new_drv_exit);//出口函数


MODULE_LICENSE("GPL");

应用程序

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


/* 休眠一段时间，无按键按下，自动返回
  */
int main(int argc, char **argv)
{
	int fd;
	unsigned char key_val;
	int ret;

	struct pollfd fds[1];
	
	fd = open("/dev/newdrv", O_RDWR);
	if (fd < 0)
	{
		printf("can't open!\n");
	}

	fds[0].fd     = fd;//文件描述符
	fds[0].events = POLLIN;//需要监测的事件
	while (1)
	{
		/*ret即mask，mask=0时，休眠等待5s*/
		ret = poll(fds, 1, 5000);
		if (ret == 0)
		{
			printf("time out\n");
		}
		else
		{
			read(fd, &key_val, 1);
			printf("key_val = 0x%x\n", key_val);
		}
	}
	return 0;
}

通用驱动makefile

KERN_DIR = /work/system/linux-3.4.2

all:
	make -C $(KERN_DIR) M=`pwd` modules 

clean:
	make -C $(KERN_DIR) M=`pwd` modules clean
	rm -rf modules.order

obj-m	+= led.o