linux字符驱动之poll机制按键驱动
2018-02-23 17:14
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在上一节中，我们讲解了如何自动创建设备节点，实现一个中断方式的按键驱动。虽然中断式的驱动，效率是蛮高的，但是大家有没有发现，应用程序的死循环里的读函数是一直在读的；在实际的应用场所里，有没有那么一种情况，偶尔有数据、偶尔没有数据，答案当然是有的。我们理想当然的就会想到，当有数据的时候，我们才去读它，没数据的时候我们读它干啥？岂不浪费劳动力？
上一节文章链接：http://blog.csdn.net/lwj103862095/article/details/17511867
这一节里，我们在中断的基础上添加poll机制来实现有数据的时候就去读，没数据的时候，自己规定一个时间，如果还没有数据，就表示超时时间。
poll机制总结：（韦老师总结的，不是我总结的哦！）
1. poll > sys_poll > do_sys_poll
>poll_initwait，poll_initwait函数注册一下回调函数__pollwait，它就是我们的驱动程序执行poll_wait时，真正被调用的函数。
2. 接下来执行file->f_op->poll，即我们驱动程序里自己实现的poll函数
它会调用poll_wait把自己挂入某个队列，这个队列也是我们的驱动自己定义的；
它还判断一下设备是否就绪。
3. 如果设备未就绪，do_sys_poll里会让进程休眠一定时间
4.
进程被唤醒的条件有2：一是上面说的“一定时间”到了，二是被驱动程序唤醒。驱动程序发现条件就绪时，就把“某个队列”上挂着的进程唤醒，这个队列，就是前面通过poll_wait把本进程挂过去的队列。
5.
如果驱动程序没有去唤醒进程，那么chedule_timeout(__timeou)超时后，会重复2、3动作，直到应用程序的poll调用传入的时间到达。
问：这一节与上一节的在驱动里添加了哪些内容？
答：仅仅添加了poll函数，该函数如下：
[cpp] view
plaincopyprint?
static unsigned int fourth_drv_poll(struct file *file, poll_table *wait)
{
unsigned int mask = 0;
poll_wait(file, &button_waitq, wait);
if(ev_press)
{
mask |= POLLIN | POLLRDNORM;
}
return mask;
}
详细请参考驱动源码：
[cpp] view
plaincopyprint?
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include //class_create
#include //S3C2410_GPF1
//#include
#include
//#include
#include //wait_event_interruptible
#include //poll
static DECLARE_WAIT_QUEUE_HEAD(button_waitq);
static struct class *fourthdrv_class;
static struct device *fourthdrv_device;
static struct pin_desc{
unsigned int pin;
unsigned int key_val;
};
static struct pin_desc pins_desc[4] = {
{S3C2410_GPF1,0x01},
{S3C2410_GPF4,0x02},
{S3C2410_GPF2,0x03},
{S3C2410_GPF0,0x04},
};
static int ev_press = 0;
static unsigned char key_val;
int major;
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)
{
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 fourth_drv_open(struct inode * inode, struct file * filp)
{
request_irq(IRQ_EINT1, buttons_irq, IRQ_TYPE_EDGE_BOTH, "K1",&pins_desc[0]);
request_irq(IRQ_EINT4, buttons_irq, IRQ_TYPE_EDGE_BOTH, "K2",&pins_desc[1]);
request_irq(IRQ_EINT2, buttons_irq, IRQ_TYPE_EDGE_BOTH, "K3",&pins_desc[2]);
request_irq(IRQ_EINT0, buttons_irq, IRQ_TYPE_EDGE_BOTH, "K4",&pins_desc[3]);
return 0;
}
static ssize_t fourth_drv_read(struct file *file, char __user *user, size_t size,loff_t *ppos)
{
if (size != 1)
return -EINVAL;
wait_event_interruptible(button_waitq, ev_press);
copy_to_user(user, &key_val, 1);
ev_press = 0;
return 1;
}
static int fourth_drv_close(struct inode *inode, struct file *file)
{
free_irq(IRQ_EINT1,&pins_desc[0]);
free_irq(IRQ_EINT4,&pins_desc[1]);
free_irq(IRQ_EINT2,&pins_desc[2]);
free_irq(IRQ_EINT0,&pins_desc[3]);
return 0;
}
static unsigned int fourth_drv_poll(struct file *file, poll_table *wait)
{
unsigned int mask = 0;
poll_wait(file, &button_waitq, wait);
if(ev_press)
{
mask |= POLLIN | POLLRDNORM;
}
return mask;
}
static const struct file_operations fourth_drv_fops = {
.owner = THIS_MODULE,
.open = fourth_drv_open,
.read = fourth_drv_read,
.release = fourth_drv_close,
.poll = fourth_drv_poll,
};
static int fourth_drv_init(void)
{
major = register_chrdev(0, "fourth_drv", &fourth_drv_fops);
fourthdrv_class = class_create(THIS_MODULE, "fourthdrv");
fourthdrv_device = device_create(fourthdrv_class, NULL, MKDEV(major, 0), NULL, "buttons");
return 0;
}
static void fourth_drv_exit(void)
{
unregister_chrdev(major, "fourth_drv");
device_unregister(fourthdrv_device); //卸载类下的设备
class_destroy(fourthdrv_class); //卸载类
}
module_init(fourth_drv_init); //用于修饰入口函数
module_exit(fourth_drv_exit); //用于修饰出口函数
MODULE_AUTHOR("LWJ");
MODULE_DESCRIPTION("Just for Demon");
MODULE_LICENSE("GPL"); //遵循GPL协议
应用测试源码：
[cpp] view
plaincopyprint?
#include
#include
#include
#include
#include
#include
int main(int argc ,char *argv[])
{
int fd;
unsigned char key_val;
struct pollfd fds;
int ret;
fd = open("/dev/buttons",O_RDWR);
if (fd < 0)
{
printf("open error\n");
}
fds.fd = fd;
fds.events = POLLIN;
while(1)
{
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;
}
测试步骤：
[cpp] view
plaincopyprint?
[WJ2440]# ls
Qt etc lib sbin third_test
TQLedtest first_drv.ko linuxrc sddisk tmp
app_test first_test mnt second_drv.ko udisk
bin fourth_drv.ko opt second_test usr
dev fourth_test proc sys var
driver_test home root third_drv.ko web
[WJ2440]# insmod fourth_drv.ko
[WJ2440]# lsmod
fourth_drv 3164 0 - Live 0xbf003000
[WJ2440]# ls /dev/buttons -l
crw-rw---- 1 root root 252, 0 Jan 2 03:00 /dev/buttons
[WJ2440]# ./fourth_test
time out
time out
key_val = 0x1
key_val = 0x81
key_val = 0x4
key_val = 0x84
key_val = 0x3
key_val = 0x83
key_val = 0x2
key_val = 0x82
^C
[WJ2440]# ./fourth_test &
[WJ2440]# time out
time out
time out
[WJ2440]#top
Mem: 10076K used, 50088K free, 0K shrd, 0K buff, 7224K cached
CPU: 0.1% usr 0.7% sys 0.0% nic 99.0% idle 0.0% io 0.0% irq 0.0% sirq
Load average: 0.00 0.00 0.00 1/23 637
PID PPID USER STAT VSZ %MEM CPU %CPU COMMAND
637 589 root R 2092 3.4 0 0.7 top
589 1 root S 2092 3.4 0 0.0 -/bin/sh
1 0 root S 2088 3.4 0 0.0 init
590 1 root S 2088 3.4 0 0.0 /usr/sbin/telnetd -l /bin/login
587 1 root S 1508 2.5 0 0.0 EmbedSky_wdg
636 589 root S 1432 2.3 0 0.0 ./fourth_test
573 2 root SW< 0 0.0 0 0.0 [rpciod/0]
5 2 root SW< 0 0.0 0 0.0 [khelper]
329 2 root SW< 0 0.0 0 0.0 [nfsiod]
2 0 root SW< 0 0.0 0 0.0 [kthreadd]
3 2 root SW< 0 0.0 0 0.0 [ksoftirqd/0]
4 2 root SW< 0 0.0 0 0.0 [events/0]
11 2 root SW< 0 0.0 0 0.0 [async/mgr]
237 2 root SW< 0 0.0 0 0.0 [kblockd/0]
247 2 root SW< 0 0.0 0 0.0 [khubd]
254 2 root SW< 0 0.0 0 0.0 [kmmcd]
278 2 root SW 0 0.0 0 0.0 [pdflush]
279 2 root SW 0 0.0 0 0.0 [pdflush]
280 2 root SW< 0 0.0 0 0.0 [kswapd0]
325 2 root SW< 0 0.0 0 0.0 [aio/0]
由测试结果可以看出，当按键没有被按下时，5秒之后，会显示出time
out，表示时间已到，在这5秒时间里，没有按键被按下，即没有数据可读，当按键按下时，立即打印出按下的按键；同时，fourth_test进程，也几乎不占用CPU的利用率。
上一节文章链接：http://blog.csdn.net/lwj103862095/article/details/17511867
这一节里，我们在中断的基础上添加poll机制来实现有数据的时候就去读，没数据的时候，自己规定一个时间，如果还没有数据，就表示超时时间。
poll机制总结：（韦老师总结的，不是我总结的哦！）
1. poll > sys_poll > do_sys_poll
>poll_initwait，poll_initwait函数注册一下回调函数__pollwait，它就是我们的驱动程序执行poll_wait时，真正被调用的函数。
2. 接下来执行file->f_op->poll，即我们驱动程序里自己实现的poll函数
它会调用poll_wait把自己挂入某个队列，这个队列也是我们的驱动自己定义的；
它还判断一下设备是否就绪。
3. 如果设备未就绪，do_sys_poll里会让进程休眠一定时间
4.
进程被唤醒的条件有2：一是上面说的“一定时间”到了，二是被驱动程序唤醒。驱动程序发现条件就绪时，就把“某个队列”上挂着的进程唤醒，这个队列，就是前面通过poll_wait把本进程挂过去的队列。
5.
如果驱动程序没有去唤醒进程，那么chedule_timeout(__timeou)超时后，会重复2、3动作，直到应用程序的poll调用传入的时间到达。
问：这一节与上一节的在驱动里添加了哪些内容？
答：仅仅添加了poll函数，该函数如下：
[cpp] view
plaincopyprint?
static unsigned int fourth_drv_poll(struct file *file, poll_table *wait)
{
unsigned int mask = 0;
poll_wait(file, &button_waitq, wait);
if(ev_press)
{
mask |= POLLIN | POLLRDNORM;
}
return mask;
}
详细请参考驱动源码：
[cpp] view
plaincopyprint?
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include //class_create
#include //S3C2410_GPF1
//#include
#include
//#include
#include //wait_event_interruptible
#include //poll
static DECLARE_WAIT_QUEUE_HEAD(button_waitq);
static struct class *fourthdrv_class;
static struct device *fourthdrv_device;
static struct pin_desc{
unsigned int pin;
unsigned int key_val;
};
static struct pin_desc pins_desc[4] = {
{S3C2410_GPF1,0x01},
{S3C2410_GPF4,0x02},
{S3C2410_GPF2,0x03},
{S3C2410_GPF0,0x04},
};
static int ev_press = 0;
static unsigned char key_val;
int major;
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)
{
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 fourth_drv_open(struct inode * inode, struct file * filp)
{
request_irq(IRQ_EINT1, buttons_irq, IRQ_TYPE_EDGE_BOTH, "K1",&pins_desc[0]);
request_irq(IRQ_EINT4, buttons_irq, IRQ_TYPE_EDGE_BOTH, "K2",&pins_desc[1]);
request_irq(IRQ_EINT2, buttons_irq, IRQ_TYPE_EDGE_BOTH, "K3",&pins_desc[2]);
request_irq(IRQ_EINT0, buttons_irq, IRQ_TYPE_EDGE_BOTH, "K4",&pins_desc[3]);
return 0;
}
static ssize_t fourth_drv_read(struct file *file, char __user *user, size_t size,loff_t *ppos)
{
if (size != 1)
return -EINVAL;
wait_event_interruptible(button_waitq, ev_press);
copy_to_user(user, &key_val, 1);
ev_press = 0;
return 1;
}
static int fourth_drv_close(struct inode *inode, struct file *file)
{
free_irq(IRQ_EINT1,&pins_desc[0]);
free_irq(IRQ_EINT4,&pins_desc[1]);
free_irq(IRQ_EINT2,&pins_desc[2]);
free_irq(IRQ_EINT0,&pins_desc[3]);
return 0;
}
static unsigned int fourth_drv_poll(struct file *file, poll_table *wait)
{
unsigned int mask = 0;
poll_wait(file, &button_waitq, wait);
if(ev_press)
{
mask |= POLLIN | POLLRDNORM;
}
return mask;
}
static const struct file_operations fourth_drv_fops = {
.owner = THIS_MODULE,
.open = fourth_drv_open,
.read = fourth_drv_read,
.release = fourth_drv_close,
.poll = fourth_drv_poll,
};
static int fourth_drv_init(void)
{
major = register_chrdev(0, "fourth_drv", &fourth_drv_fops);
fourthdrv_class = class_create(THIS_MODULE, "fourthdrv");
fourthdrv_device = device_create(fourthdrv_class, NULL, MKDEV(major, 0), NULL, "buttons");
return 0;
}
static void fourth_drv_exit(void)
{
unregister_chrdev(major, "fourth_drv");
device_unregister(fourthdrv_device); //卸载类下的设备
class_destroy(fourthdrv_class); //卸载类
}
module_init(fourth_drv_init); //用于修饰入口函数
module_exit(fourth_drv_exit); //用于修饰出口函数
MODULE_AUTHOR("LWJ");
MODULE_DESCRIPTION("Just for Demon");
MODULE_LICENSE("GPL"); //遵循GPL协议
应用测试源码：
[cpp] view
plaincopyprint?
#include
#include
#include
#include
#include
#include
int main(int argc ,char *argv[])
{
int fd;
unsigned char key_val;
struct pollfd fds;
int ret;
fd = open("/dev/buttons",O_RDWR);
if (fd < 0)
{
printf("open error\n");
}
fds.fd = fd;
fds.events = POLLIN;
while(1)
{
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;
}
测试步骤：
[cpp] view
plaincopyprint?
[WJ2440]# ls
Qt etc lib sbin third_test
TQLedtest first_drv.ko linuxrc sddisk tmp
app_test first_test mnt second_drv.ko udisk
bin fourth_drv.ko opt second_test usr
dev fourth_test proc sys var
driver_test home root third_drv.ko web
[WJ2440]# insmod fourth_drv.ko
[WJ2440]# lsmod
fourth_drv 3164 0 - Live 0xbf003000
[WJ2440]# ls /dev/buttons -l
crw-rw---- 1 root root 252, 0 Jan 2 03:00 /dev/buttons
[WJ2440]# ./fourth_test
time out
time out
key_val = 0x1
key_val = 0x81
key_val = 0x4
key_val = 0x84
key_val = 0x3
key_val = 0x83
key_val = 0x2
key_val = 0x82
^C
[WJ2440]# ./fourth_test &
[WJ2440]# time out
time out
time out
[WJ2440]#top
Mem: 10076K used, 50088K free, 0K shrd, 0K buff, 7224K cached
CPU: 0.1% usr 0.7% sys 0.0% nic 99.0% idle 0.0% io 0.0% irq 0.0% sirq
Load average: 0.00 0.00 0.00 1/23 637
PID PPID USER STAT VSZ %MEM CPU %CPU COMMAND
637 589 root R 2092 3.4 0 0.7 top
589 1 root S 2092 3.4 0 0.0 -/bin/sh
1 0 root S 2088 3.4 0 0.0 init
590 1 root S 2088 3.4 0 0.0 /usr/sbin/telnetd -l /bin/login
587 1 root S 1508 2.5 0 0.0 EmbedSky_wdg
636 589 root S 1432 2.3 0 0.0 ./fourth_test
573 2 root SW< 0 0.0 0 0.0 [rpciod/0]
5 2 root SW< 0 0.0 0 0.0 [khelper]
329 2 root SW< 0 0.0 0 0.0 [nfsiod]
2 0 root SW< 0 0.0 0 0.0 [kthreadd]
3 2 root SW< 0 0.0 0 0.0 [ksoftirqd/0]
4 2 root SW< 0 0.0 0 0.0 [events/0]
11 2 root SW< 0 0.0 0 0.0 [async/mgr]
237 2 root SW< 0 0.0 0 0.0 [kblockd/0]
247 2 root SW< 0 0.0 0 0.0 [khubd]
254 2 root SW< 0 0.0 0 0.0 [kmmcd]
278 2 root SW 0 0.0 0 0.0 [pdflush]
279 2 root SW 0 0.0 0 0.0 [pdflush]
280 2 root SW< 0 0.0 0 0.0 [kswapd0]
325 2 root SW< 0 0.0 0 0.0 [aio/0]
由测试结果可以看出，当按键没有被按下时，5秒之后，会显示出time
out，表示时间已到，在这5秒时间里，没有按键被按下，即没有数据可读，当按键按下时，立即打印出按下的按键；同时，fourth_test进程，也几乎不占用CPU的利用率。
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