字符设备驱动程序之poll机制

驱动源码：

#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”

int major = 0;

static struct class *keydrv_class;

static struct class_device *keydrv_class_dev;

volatile unsigned long *gpfcon;

volatile unsigned long *gpfdat;

volatile unsigned long *gpgcon;

volatile unsigned long *gpgdat;

struct pin_desc{

unsigned int pin;

unsigned int key_val;

};

struct pin_desc pins_desc[4] = {

{S3C2410_GPF0, 0x01},

{S3C2410_GPF2, 0x02},

{S3C2410_GPG3, 0x03},

{S3C2410_GPG11, 0x04},

};

// 键值: 按下时, 0x01, 0x02, 0x03, 0x04

// 键值: 松开时, 0x81, 0x82, 0x83, 0x84

static unsigned char key_val;

static DECLARE_WAIT_QUEUE_HEAD(button_waitq);

// 中止事情标志, 中止服务程序将它置1，third_drv_read将它清0

static volatile int ev_press = 0;

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

{

// 按下

key_val = pindesc->key_val;

}

ev_press = 1; // 表明中止发生了

wake_up_interruptible(&button_waitq); // 唤醒休眠的进程

return IRQ_RETVAL(IRQ_HANDLED);

}

static int key_drv_open(struct inode *inode, struct file *file)

{

request_irq(IRQ_EINT0, buttons_irq,IRQT_BOTHEDGE,”S2″,&pins_desc[0]);

request_irq(IRQ_EINT2, buttons_irq,IRQT_BOTHEDGE,”S3″,&pins_desc[1]);

request_irq(IRQ_EINT11,buttons_irq,IRQT_BOTHEDGE,”S4″,&pins_desc[2]);

request_irq(IRQ_EINT19,buttons_irq,IRQT_BOTHEDGE,”S5″,&pins_desc[3]);

return 0;

}

ssize_t key_drv_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)

{

if(size != sizeof(key_val))

return -EINVAL;

// 假如没有按键动作, 休眠

wait_event_interruptible(button_waitq, ev_press);

// 假如有按键动作, 回来键值

copy_to_user(buf, &key_val, 1);

ev_press = 0;

return 1;

}

int key_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 unsigned key_drv_poll(struct file *file, poll_table *wait)

{

unsigned int mask = 0;

poll_wait(file, &button_waitq, wait); // 不会当即休眠

if (ev_press)

mask |= POLLIN | POLLRDNORM; //有数据可读

return mask;

}

static struct file_operations key_drv_fops = {

.owner = THIS_MODULE, // 这是一个宏，面向编译模块时主动创立的__this_module变量

.open = key_drv_open,

.read = key_drv_read,

.release = key_drv_close,

.poll = key_drv_poll,

};

static int key_drv_init(void)

{

major = register_chrdev(0, “key_drv”, &key_drv_fops);

keydrv_class = class_create(THIS_MODULE, “key_drv”);

keydrv_class_dev = class_device_create(keydrv_class, NULL, MKDEV(major, 0), NULL, “buttons”);

gpfcon = (volatile unsigned long *)ioremap(0x56000050, 16);

gpfdat = gpfcon + 1;

gpgcon = (volatile unsigned long *)ioremap(0x56000060, 16);

gpgdat = gpgcon + 1;

return 0;

}

static void key_drv_exit(void)

{

unregister_chrdev(major, “key_drv”);

class_device_unregister(keydrv_class_dev);

class_destroy(keydrv_class);

iounmap(gpfcon);

iounmap(gpgcon);

return 0;

}

module_init(key_drv_init);

module_exit(key_drv_exit);

MODULE_LICENSE(“GPL”);

=================================================================

测验源码：

#include

int main(int argc, char **argv)

{

int fd;

unsigned char key_vals;

int ret;

struct pollfd fds[1];

fd = open(“/dev/buttons”, O_RDWR);

if(fd < 0)

printf(“cant open!\n”);

fds[0].fd = fd;

fds[0].events = POLLIN;

while(1)

{

ret = poll(fds, 1, 5000); //5000是毫秒为单位，等候5S钟判别fds[0].fd文件是否有新数据可读

if(ret == 0)

{

printf(“time out !\n”); //超时

}

else

{

read(fd, &key_vals, 1); //有数据可读

printf(“key_vals = 0x%x\n”, key_vals);

}

return 0;

}

==================================================================

解析：

1、key_drv_fops 结构体中添加：.poll = key_drv_poll,

key_drv_poll函数就去查询有没有按键值更新（/dev/buttons），假如按键按下则回来，不然休眠，比及休眠时刻到则主动回来；

2、应用程序中循环调用poll函数，判别按键值有没有更新；假如更新则读取，不然超时提示。

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