poll机制

使用POLL机制代替linux输入子系统（input subsystem）之按键输入和LED控制中的异步通知，实现同样的效果。

1.代码

只简单修改input_subsys_test.c， input_subsys_drv.c不变

input_subsys_test.c

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

 #include <linux/input.h>

 int fd;

 void my_signal_fun(int signum)
 {
     struct input_event buttons_event, leds_event;

     /* [cgw]: 异步通知产生时返回的数据 */
     read(fd, &buttons_event, sizeof(struct input_event));

     /* [cgw]: 打印事件类型，事件码，事件值 */
     printf("type: 0x%x code: 0x%x value: 0x%x\n",
            buttons_event.type,
            buttons_event.code,
            buttons_event.value);

     /* [cgw]: 返回的是KEY_L或KEY_S值 */
     if (buttons_event.code == KEY_L || buttons_event.code == KEY_S) {
         /* [cgw]: 按键弹起 */
         if (buttons_event.value == ) {

             /* [cgw]: 构造一个EV_LED事件 */

             //leds_event.type = EV_SND;
             leds_event.type = EV_LED;
             //leds_event.code = SND_BELL;
             leds_event.code = LED_MUTE;

             /* [cgw]: KEY_L和KEY_S控制LED的亮灭 */
             if (buttons_event.code == KEY_L) {
                 leds_event.value = 0xAA;
             } else if (buttons_event.code == KEY_S) {
                 leds_event.value = 0xEE;
             }

             /* [cgw]: 发送LED控制事件 */
             write(fd, &leds_event, sizeof(struct input_event));

             printf("led write!\n");
         }
     }
 }

 int main(int argc, char **argv)
 {
     int ret, arg;
     struct pollfd fds[];

     fd = open("/dev/event1", O_RDWR | O_NONBLOCK);

     //printf("fd = 0x%x\n", fd);

     if (fd < )
     {
         printf("can't open!\n");
     }

     /* [cgw]: 设置文件标识符 */
     fds[].fd     = fd;
     /* [cgw]: 设置应用程序要响应的事件 */
     fds[].events = POLLIN;

     while ()
     {
         /* [cgw]: 休眠5S */
         ret = poll(fds, , );

         /* [cgw]: 唤醒或超时 */
         printf("wake up!\n");
         if (ret == )
         {
             printf("time out\n");
         }
         else
         {
             my_signal_fun(arg);
         }
     }

     return ;
 }

2. 实验

2.1

安装驱动程序：

insmod input_subsys_drv.ko

 # insmod input_subsys_drv.ko
 input: input_subsys_dev as /class/input/input1
 input subsys open!
 input subsys init!

运行应用程序

./input_subsys_test

 # ./input_subsys_test
 wake up!
 type: 0x1 code: 0x26 value: 0x1
 wake up!
 type: 0x1 code: 0x26 value: 0x0
 led event!
 value: 0xaa
 led write!
 wake up!
 type: 0x11 code: 0x7 value: 0xaa
 wake up!
 type: 0x1 code: 0x1f value: 0x1
 wake up!
 type: 0x1 code: 0x1f value: 0x0
 led event!
 value: 0xee
 led write!
 wake up!
 type: 0x11 code: 0x7 value: 0xee
 wake up!
 type: 0x1 code: 0x1c value: 0x1
 wake up!
 type: 0x1 code: 0x1c value: 0x0
 wake up!
 time out
 wake up!
 time out

3. 现象分析

按一下按键KEY_L，终端输出：

 wake up!
 type: 0x1 code: 0x26 value: 0x1
 wake up!
 type: 0x1 code: 0x26 value: 0x0
 led event!
 value: 0xaa
 led write!
 wake up!
 type: 0x11 code: 0x7 value: 0xaa