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控制GPIO

Input-Output Linux Gist
字数统计: 447阅读时长: 2 min
2018/10/13 Share

Control GPIO in C code user space

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#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>

#define PANELVCC_VALUE "/sys/class/gpio/gpio31/value"
#define PANELVCC_DIRECTION "/sys/class/gpio/gpio31/direction"

int main()
{
    int valuefd, directionfd;
    // Update the direction of the GPIO to be an output
    directionfd = open(PANELVCC_DIRECTION, O_RDWR);
    if (directionfd < 0)
    {
        printf("Cannot open GPIO direction it\n");
        exit(1);
    }
    write(directionfd, "out", 4);
    close(directionfd);
    printf("GPIO direction set as output successfully\n");

    // Get the GPIO value ready to be toggled
    valuefd = open(PANELVCC_VALUE, O_RDWR);
    if (valuefd < 0)
    {
        printf("Cannot open GPIO value\n");
        exit(1);
    }
    printf("GPIO value opened, now toggling...\n");

    // toggle the GPIO as fast a possible forever, a control c is needed to stop it
    while (1)
    {
        write(valuefd,"0", 2);
        printf("Panel Vcc, set low...\n");
        sleep(5);
        write(valuefd,"1", 2);
        printf("Panel Vcc, set high...\n");
        sleep(5);
    }
}

应用层调用kernel gpio接口需要用到/sys/class/gpio， 其中内容如下:

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root@xxx:/sys/class/gpio # ls
    export     //创建一个gpio节点
    gpio1      //单个GPIO控制节点
    gpio2      //单个GPIO控制节点
    ...
    gpiochip0  //一组GPIO控制节点
    unexport   //移除一个gpio节点

命令行方式:
echo 3 > export // 在/sys/class/gpio/下生成1个gpio3节点
以GPIO3为例:

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root@xxxx:/sys/class/gpio/gpio3 # ls -l
-rw-r--r-- root     root         4096 1970-01-01 08:10 active_low //0:不反转, 1： 反转(反转时value=1 为低电平)
-rw-r--r-- root     root         4096 1970-01-01 08:10 direction  //gpio 输入/输出， in or out
drwxr-xr-x root     root              1970-01-01 08:00 power
lrwxrwxrwx root     root              1970-01-01 08:10 subsystem -> ../../../../class/gpio
-rw-r--r-- root     root         4096 1970-01-01 08:00 uevent
-rw-r--r-- root     root         4096 1970-01-01 08:10 value  //gpio 电平状态， 0 or 1

通用的还有edge设置中断触发方式，设置为in时才有。
none表示引脚为输入，不是中断引脚
rising表示引脚为中断输入，上升沿触发
falling表示引脚为中断输入，下降沿触发
both表示引脚为中断输入，边沿触发

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  1. 1. Control GPIO in C code user space
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