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我试图在它改变状态时使用它来读取 GPIO 值。

/sys/class/gpio/gpio499/value

我已经设置/sys/class/gpio/gpio499/edge两者

我正在尝试在一个单独的线程中使用poll命令监视值的变化。这是代码片段:

void PIN_gpio_poll(size_t gpio)     //GPIO 499
{
        char path[30];
        char cValue;
        int fd;
        int ret_poll;
        int ret_read;
        struct pollfd pollfd;
        int i;

        pollfd.events = POLLPRI | POLLERR; /* look for GPIO status change. */


        snprintf(path, 30, PHDRIVER_LINUX_CFG_DIR "/gpio%u/value", gpio);
        fd = open(path, O_RDONLY);
        if (fd == -1)
        {
                printf("Gpio_poll _ERROR\r\n");
        }

        pollfd.fd = fd;

        ret_read = read(pollfd.fd, &cValue, 1);    // Dummy Read to clear

        while (1)
        {
                lseek(fd, 0, SEEK_SET);
                ret_read = read(fd, &cValue, 1);
                printf("Value=%c, RET READ=%d\n",cValue,ret_read);
//              ret_poll = poll( &pollfd, 1, -1 );
                ret_poll = poll( &pollfd, 1, 10000 );  //10sec timeout

                printf("******REVENTS=%x\n",pollfd.revents);
                if( ret_poll == -1 )
                {
                        printf("Gpio_poll poll failed\r\n");
                        close(fd);
                }else{
//                      if (pollfd.revents & POLLPRI )
                        {
                                lseek(fd, 0, SEEK_SET);
                                ret_read = read(pollfd.fd, &cValue, 1);
                                if(ret_read > 0)
                                {
                                    printf("Cvalue = %c\n",cValue);
                                }
                        }

                }
        }
}

我面临的问题是,如果我将事件设置为POLLIN,则 poll 会立即返回。这是可以理解的,因为在值(0 或 1)GPIO中总是有要读取的数据。我提到 了https://www.kernel.org/doc/Documentation/gpio/sysfs.txt并将事件设置为 POLLPRI | 轮询。但在此方法中,轮询仅在超时后返回。当 GPIO 的值改变时它不会返回。有什么我在这里错过的诀窍吗?我也设置/sys/class/gpio/gpio499/edge了上升,下降,但似乎没有任何效果。

编辑:这是输出grep -r . /sys/class/gpio/gpio499

/sys/class/gpio/gpio499/edge:both
/sys/class/gpio/gpio499/power/control:auto
/sys/class/gpio/gpio499/power/runtime_active_time:0
grep: /sys/class/gpio/gpio499/power/autosuspend_delay_ms: Input/output error
/sys/class/gpio/gpio499/power/runtime_status:unsupported
/sys/class/gpio/gpio499/power/runtime_suspended_time:0
/sys/class/gpio/gpio499/value:1
/sys/class/gpio/gpio499/active_low:0
/sys/class/gpio/gpio499/direction:in

注意:我想检测从 1 到 0 的值。

4

1 回答 1

0

功能:poll()不像发布的代码所期望的那样工作。

建议:1)读取文件获取当前输入值。2)执行一个自旋循环,读取值,直到值发生变化,类似于:

readbytes = read( fd, &cValue, 1 );  
while( readbytes > 0 )
{  
    if( (off_t)-1 == lseek(fd, 0, SEEK_SET) )
    { // then lseek failed
        perror( "lseek failed" );
        exit( EXIT_FAILURE );
    }

    // implied else, lseek successful

    readbytes = read(fd, &new_cValue, 1);
    if( 0 >= readbytes )
    { 
        perror( "read failed" );
        exit( EXIT_FAILURE );
    }

    // implied else, read successful

    if( cValue != new_cValue )
    { // then state changed
        cValue = new_cValue;
        break;
    }
}

这个循环确实会消耗更多的 CPU 周期,但应该可以工作

于 2017-10-19T21:01:52.110 回答