8.中断按键驱动程序之poll机制

while ()
{
read(fd, &key_val, );
printf("key_val = 0x%x\n", key_val);
}

asmlinkage long sys_poll(struct pollfd __user *ufds, unsigned int nfds,long timeout_msecs)
{
if (timeout_msecs > ) //参数timeout>0
{
timeout_jiffies = msecs_to_jiffies(timeout_msecs); //通过频率来计算timeout时间需要多少计数值
}
else
{
timeout_jiffies = timeout_msecs; //如果timeout时间为0,直接赋值
}
return do_sys_poll(ufds, nfds, &timeout_jiffies); //调用do_sys_poll。
}

int do_sys_poll(struct pollfd __user *ufds, unsigned int nfds, s64 *timeout)
{
... ...
/*初始化一个poll_wqueues变量table*/
poll_initwait(&table);
... ...
fdcount = do_poll(nfds, head, &table, timeout);
... ...
}

table ->pt-> qproc=__pollwait; //__pollwait将在驱动的poll函数里的poll_wait函数用到

static int do_poll(unsigned int nfds, struct poll_list *list, struct poll_wqueues *wait, s64 *timeout)
{
……
for (;;)
{
……
set_current_state(TASK_INTERRUPTIBLE); //设置为等待队列状态
......
for (; pfd != pfd_end; pfd++) { //for循环运行多个poll机制
/*将pfd和pt参数代入我们驱动程序里注册的poll函数*/
if (do_pollfd(pfd, pt)) //若返回非0,count++,后面并退出
{ count++;
pt = NULL; } }……/*count非0(.poll函数返回非0)，timeout超时计数到0,有信号在等待*/ if (count || !*timeout || signal_pending(current))
break;
……

/*进入休眠状态,只有当timeout超时计数到0,或者被中断唤醒才退出,*/
__timeout = schedule_timeout(__timeout);…… }__set_current_state(TASK_RUNNING); //开始运行
return count;}

static inline unsigned int do_pollfd(struct pollfd *pollfd, poll_table *pwait)
{
……
if (file->f_op && file->f_op->poll)
mask = file->f_op->poll(file, pwait);
……return mask;
}

#include <linux/poll.h> //添加头文件

/* .poll驱动函数: third_poll */
static unsigned int third_poll(struct file *fp, poll_table * wait) //fp:文件 wait:
{
unsigned int mask =;
poll_wait(fp, &button_wait, wait);
if(even_press) //中断事件标志, 1:退出休眠状态 0:进入休眠状态
mask |= POLLIN | POLLRDNORM ;
return mask; //当超时,就返给应用层为0 ,被唤醒了就返回POLLIN | POLLRDNORM ;}static struct file_operations third_drv_fops={
.owner = THIS_MODULE,
.open = third_drv_open,
.read = third_drv_read,
.release=third_drv_class,
.poll = third_poll, //创建.poll函数
};

if (do_pollfd(pfd, pt)) //若返回非0,count++,后面并退出
{
count++;
pt = NULL;
}

poll_wait(fp, &button_wait, wait);

table ->pt-> qproc=__pollwait;

static void __pollwait(struct file *filp, wait_queue_head_t *wait_address,poll_table *p)
{
... ...
//把current进程挂载到&entry->wait下
init_waitqueue_entry(&entry->wait, current); //再&entry->wait把添加到到button_wait中断下
add_wait_queue(wait_address, &entry->wait);}

int poll(struct pollfd *fds, nfds_t nfds, int timeout);

struct pollfd {
int fd; /* file descriptor 文件描述符*/
short events; /* requested events 请求的事件*/
short revents; /* returned events 返回的事件(函数返回值)*/
};

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <poll.h> //添加poll头文件/*useg: thirdtext */
int main(int argc,char **argv)
{
int fd,ret;
unsigned int val=;
struct pollfd fds; //定义poll文件描述结构体
fd=open("/dev/buttons",O_RDWR);
if(fd<)
{printf("can't open!!!\n");
return -;} fds.fd=fd;
fds.events= POLLIN; //请求类型是 普通或优先级带数据可读 while()
{ ret=poll(&fds,,) ; //一个poll, 定时5000ms,进入休眠状态
if(ret==) //超时
{
printf("time out \r\n");
}
else if(ret>) //poll机制被唤醒，表示有数据可读
{
read(fd,&val,); //读取一个值
printf("key_val=0X%x\r\n",val);
}
}
return ;
}