linux驱动编写之poll机制

uint8_t I2C_WaitForEvent(I2C_TypeDef* I2Cx, uint32_t I2C_EVENT,int32_t delay)
{    

    while(!I2C_CheckEvent(I2Cx, I2C_EVENT) && (delay-- > 0));
    
    if(delay < 0){
        return 0;
    }
    
    return 1;
}

int8_t I2C_EE_PageWrite(u8* pBuffer, u16 WriteAddr, u8 NumByteToWrite)
{
      .............
      if(I2C_WaitForEvent(I2C1, I2C_EVENT_MASTER_BYTE_TRANSMITTED, 100000) != 1){
            return -1;
      }
      ............
}

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <poll.h>

int main(int argc, char **argv)
{
    int i;
    int ret;
    int fd;
    unsigned char keys_val;
    struct pollfd fds[1];
    
    fd = open("/dev/buttons", 0);  // 打开设备
    if (fd < 0) {
        printf("Can't open /dev/buttons\n");
        return -1;
    }

    fds[0].fd = fd;
    fds[0].events = POLLIN;
    
    while (1) {
        ret = poll(fds,1, 5000);
        if(ret == 0)
        {
            printf("time out!\n");
        }
        else
        {
            read(fd, &keys_val, sizeof(keys_val));
            printf("keys_val = 0x%x\n",keys_val);
        }
    }
    
    close(fd);
    return 0;    
}

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

/* 定义一个等待队列，这个等待队列其实是由中断驱动的，当中断发生时，会令挂接到这个等待队列的休眠进程唤醒 */
static DECLARE_WAIT_QUEUE_HEAD(button_waitq);

static unsigned drivers_poll(struct file *file, poll_table *wait)
{
    unsigned int mask = 0;
    poll_wait(file, &button_waitq, wait); /* 将进程挂接到button_waitq等待队列下 */

    /* 根据实际状况，标记事件类型 */ if (ev_press)
        mask |= POLLIN | POLLRDNORM;

    /* 若是mask为0，那么证实没有请求事件发生；若是非零说明有时间发生 */ return mask;
}

app: poll
      |
drv:sys_poll
      |
      — do_sys_poll(struct pollfd __user * ufds, unsigned int nfds, struct timespec * end_time)
        |   
        - poll_initwait(&table);  >  实际效果：令函数指针 table.pt.qproc = __pollwait，这个函数指针最终会传递给poll_wait函数调用中的wait->qproc
        |
        - do_poll(nfds, head, &table, end_time);
        |
        _ for ( ; ; )
          {
                for (; pfd != pfd_end; pfd++) {    /* 能够监测多个驱动设备所产生的事件 */ if (do_pollfd(pfd, pt)) {  
                      |
                      _  mask = file->f_op->poll(file, pwait); > 实际效果：执行咱们写的drivers_poll(file,pwait)

                                |
                                 _  poll_wait(file, &button_waitq, wait); > 实际效果：执行__pollwait(file, &button_waitq, wait)，也就是将
 进程挂接到button_waitq等待队列下
                                |
                          —  mask赋值 ; return mask; /* 返回事件类型 */

                         pollfd->revents = mask;    /* 将实际事件类型返回 */
                         count++; pt = NULL; 
                     } 
                 } 
               if (count || timed_out) /* 若是有事件发生，或者超时，则跳出poll */ 
 break; 
               if (!poll_schedule_timeout(wait, TASK_INTERRUPTIBLE, to, slack)) /* 若是没有事件发生，那么陷入休眠状态 */ 
                  timed_out = 1; 
          }