（2）ARM40-A5板应用程序——GPIO输出高低电平

2017.03.19

一、在 shell 中控制一个IO的高低电平

(1) echo 138 > /sys/class/gpio/export // 138对应的是E10，输入这个命令后，即出现/sys/class/gpio/pioE10

(2) echo out > /sys/class/gpio/pioE10/direction // 设置E10为 out

(3) echo 1 > /sys/class/gpio/pioE10/value // 设置E10为高电平，此时万用表可测得E10的确为高电平

(4) echo 0 > /sys/class/gpio/pioE10/value // 设置E10为低电平，此时万用表可测得E10的确为低电平

(5) echo 138 > /sys/class/gpio/unexport // 不再使用时，需要unexport

在 imx6板上，gpioP_N对应的引脚编号为 nr = (P-1)*32 + N。例如 gpio6_8对应168 = (6-1)*32+8，上面的五条命令稍有不同：

(1) echo 168 > /sys/class/gpio/export // 168对应的是gpio6_8，输入这个命令后，即出现/sys/class/gpio/gpio168

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(2) echo out > /sys/class/gpio/gpio168/direction

(3) echo 1 > /sys/class/gpio/gpio168/value

(4) echo 0 > /sys/class/gpio/gpio168/value

(5) echo 168 > /sys/class/gpio/unexport

二、GPIO输出高低电平的C语言源码

文件名为 test_pioE10.c，代码见本文附录（1）。该代码的核心就是第一节中的5句命令。

三、交叉编译

arm-none-linux-gnueabi-gcc -o test_pioE10 test_pioE10.c -static

四、执行程序

将交叉编译得到的 test_pioE10 文件拷贝到ARM40-A5板中，执行程序：

./test_pioE10

用示波器即可观察到E10这个IO上出现高低电平的变化。

五、较多GPIO的C语言源码

文件名为 test_gpio.c，代码见本文附录（2）。

将交叉编译得到的 test_gpio 文件拷贝到ARM40-A5板中，执行程序：

./test_gpio E10

用示波器即可观察到E10这个IO上出现高低电平的变化。

参考文章：

http://blog.csdn.net/luyejie8888/article/details/38172705

BeagleBone Black板第四课：简单LED控制实验

http://blog.csdn.net/luyejie8888/article/details/38361525

BeagleBone Black板第五课：Shell脚本编程实验

https://developer.ridgerun.com/wiki/index.php/How_to_use_GPIO_signals

How_to_use_GPIO_signals

http://blog.csdn.net/drivermonkey/article/details/20132241?utm_source=tuicool

LinuxGPIO驱动使用其实很简单

附：

（1）test_pioE10.c 的代码

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

static inline int write_str(const char* dest, const char *str);

int main(int argc, char **argv)
{
        int count = 5;

        if(write_str("/sys/class/gpio/export", "138")) return(-1);
        if(write_str("/sys/class/gpio/pioE10/direction","out")) return(-1);

        while(count--) {
                write_str("/sys/class/gpio/pioE10/value","1");
                sleep(2);
                write_str("/sys/class/gpio/pioE10/value","0");
                sleep(2);
        }

        if(write_str("/sys/class/gpio/unexport", "138")) return(-1);
        printf("finish!\n");
        return 0;
}

static inline int write_str(const char* dest, const char *str)
{
        int fd;

        if((fd = open(dest, O_WRONLY)) < 0) {
                perror(str);
                return(fd);
        }
        write(fd, str, strlen(str)+1);        // Include null '\0'
        close(fd);
        return(0);
}

（2）test_gpio.c 的代码

/* 
 * 注： 
 * 随意指定io可能会报错，例如： 
 * PC31已为蜂鸣器BUZZ，如果在本程序中也包含进来，运行程序的时候会报： 
 *  sh: write error: Device or resource busy   
 */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>

#define MAX_BUF 64
//只有gpio_name_list中的io才会被接受
static char* gpio_name_list[] = {
        "B19","B20","B21","B22","B23","B24","B25","B26","B27","B28","B29",                  //51,52,...61
        "C22","C23","C24","C25","C26","C27","C28",                                          //86,87,...92
        "D5","D6","D7","D8","D16","D17","D18","D19","D20","D21","D22","D23","D28","D30",    //101,102,...126
       "E3","E5","E10","E15","E16","E17","E18","E19","E20","E23","E24","E25","E26","E31",   //131,133,...159
        NULL
};

int gpio_name_match(char* gpio_name);
static inline int write_str(const char* dest, const char *str);
int gpio_output_open(const char* gpio_name);
int gpio_io_close(const char* gpio_name);

int main(int argc, char **argv)
{
        int count = 5;
        int fd;

        if(2 != argc) { // 命令为 ./test_gpio E10， 如果不是两个参数，则报错  
                printf("ERR: need 1 arg.\n ");
                printf("eg: ./test_gpio %s\n", argv[1]);
                return -1;
        }

        if(0 != gpio_name_match(argv[1])) {
                printf("err: argv[1]=%s isn't allowed\n",argv[1]);
                return -1;
        }
    
        if((fd = gpio_output_open(argv[1])) < 0)    // eg: open /sys/class/gpio/pioE10/value
                return -1;

        while(count--) {
                write(fd, "1", sizeof("1"));
                sleep(2);
                write(fd, "0", sizeof("0"));
                sleep(2);
        }

        close(fd);
        gpio_io_close(argv[1]);

        printf("finish!\n");
        return 0;
}

// eg: str=E10, return 0;
// eg: str=E111, return -1;
int gpio_name_match(char* gpio_name)
{
        int i;

        for(i=0; gpio_name_list[i]!=NULL; i++) {
                if(0 == strcmp(gpio_name_list[i], gpio_name))
                        return 0;
        }

        return -1; //在字符串数组中未找到，则返回-1
}

static inline int write_str(const char* dest, const char *str)
{
        int fd;

        if((fd = open(dest, O_WRONLY)) < 0) {
                perror(str);
                return(fd);
        }
        write(fd, str, strlen(str)+1); // Include null '\0'
        close(fd);
        return(0);
}

int gpio_output_open(const char* gpio_name)
{
        int fd;
        int gpio_id;
        char gpio_id_str[4];
        char buf[64];

        gpio_id = ((gpio_name[0]-'A') << 5) + atoi(gpio_name+1);        //eg: gpio_name="E10", gpio_id=138
        snprintf(gpio_id_str, sizeof(gpio_id_str), "%d", gpio_id);      //eg: gpio_id_str="138"
        if(write_str("/sys/class/gpio/export", gpio_id_str))    return(-1);

        snprintf(buf, sizeof(buf), "/sys/class/gpio/pio%s/direction", gpio_name);
        if(write_str(buf,"out"))        goto err;

        snprintf(buf, sizeof(buf), "/sys/class/gpio/pio%s/value", gpio_name);
        if((fd = open(buf, O_WRONLY)) < 0)    goto err;

        return fd;

err:
        write_str("/sys/class/gpio/unexport", gpio_id_str);
        return(-1);
}

int gpio_io_close(const char* gpio_name)
{
        int gpio_id;
        char gpio_id_str[4];

        gpio_id = ((gpio_name[0]-'A') << 5) + atoi(gpio_name+1);        //eg: gpio_name="E3", gpio_id=131
        snprintf(gpio_id_str, sizeof(gpio_id_str), "%d", gpio_id);      //eg: gpio_id_str="131"
        if(write_str("/sys/class/gpio/unexport", gpio_id_str))
                return(-1);

        return 0;
}

（2）ARM40-A5板应用程序——GPIO输出高低电平

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