（2）ARM40-A5板应用程序——GPIO输出高低电平
2017.03.19
(1) echo 138 > /sys/class/gpio/export // 138对应的是pioE10，输入这个命令后，即出现/sys/class/gpio/pioE10
(2) echo out > /sys/class/gpio/pioE10/direction // 设置pioE10为 out
(3) echo 1 > /sys/class/gpio/pioE10/value // 设置pioE10为高电平，此时万用表可测得pioE10的确为高电平
(4) echo 0 > /sys/class/gpio/pioE10/value // 设置pioE10为低电平，此时万用表可测得pioE10的确为低电平
(5) echo 138 > /sys/class/gpio/unexport // 不再使用时，需要unexport
二、GPIO输出高低电平的C语言源码
文件名为 test_gpio.c，代码见本文的最后。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_gpio test_gpio.c -static
四、执行程序
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 pioE10
用示波器即可观察到pioE10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
附：
（1）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>
#include <termios.h>
#define MAX_BUF 36
#define STR_GPIO struct { \
char* gpio; \
char* num; \
}
/**
* STR_GPIO 结构体把类似pioE10与138这样的对应关系罗列出来
* 只有出现在这个结构体中的io，才能被该程序执行到，没有出现的，如果命令行输入了，会报错
* 请谨慎使用这里的io
*/
STR_GPIO str_io[] = {
{"pioE31","159"},
{"pioE5","133"},
{"pioE3","131"},
{"pioE10","138"},
{"pioD28","124"},
{"pioD30","126"},
{"pioD23","119"},
{"pioD22","118"},
{"pioD21","117"},
{"pioD20","116"},
{"pioD19","115"},
{"pioD18","114"},
{"pioD17","113"},
{"pioD16","112"},
{"pioE20","148"},
{"pioE23","151"},
{"pioE24","152"},
{"pioE25","153"},
{"pioE26","154"},
{"pioE19","147"},
{"pioE18","146"},
{"pioE17","145"},
{"pioE16","144"},
{"pioE15","143"},
{"pioB25","57"},
{"pioB26","58"},
{"pioB27","59"},
{"pioB28","60"},
{"pioB29","61"},
{"pioC22","86"},
{"pioC23","87"},
{"pioC24","88"},
{"pioC25","89"},
{"pioC26","90"},
{"pioC27","91"},
{"pioC28","92"},
{"pioB24","56"},
{"pioB23","55"},
{"pioB22","54"},
{"pioB21","53"},
{"pioB20","52"},
{"pioB19","51"},
// {"pioD0","96"},
// {"pioD1","97"},
// {"pioD2","98"},
// {"pioD3","99"},
// {"pioD4","100"},
{"pioD5","101"},
{"pioD6","102"},
{"pioD7","103"},
{"pioD8","104"},
// {"pioD9","105"},
{}
};
int gpio_export(char* ver);
int gpio_unexport(char* ver);
int gpio_set_dir(char* str);
int gpio_set_value(char *str, unsigned int value);
int match_ver(char* str, char *ver);
int gpio_flash(char* str);
/*
* 执行程序 ./test_gpio pioE10
*/
int main(int argc, char** argv)
{
char ver[3];
if(2 != argc) { // 命令为 ./test_gpio pioE10， 如果不是两个参数，则报错
printf("ERR: need 1 arg.\n ");
return -1;
}
printf("eg:pioE10, argv[1]=%s\n", argv[1]);
if(match_ver(argv[1], ver)) {
printf("err: argv[1]=%s isn't enabled\n",argv[1]);
return -1;
}
gpio_export(ver); // echo 138 > /sys/class/gpio/export
gpio_flash(argv[1]); // eg: argv[1]=pioE10
gpio_unexport(ver); // echo 138 > /sys/class/gpio/unexport
printf("finish!\n");
return 0;
}
// eg: str=pioE10, ver=138, return 0;
// eg: str=pioE111, return 1;
int match_ver(char* str, char *ver)
{
int i;
for(i=0; str_io[i].gpio!=NULL; i++) {
if(0 == strcmp(str_io[i].gpio, str)) {
strcpy(ver, str_io[i].num);
return 0;
}
}
return 1; // 如果在结构体列表中没有找到，则返回1
}
// eg: ver=138
// echo 138 > /sys/class/gpio/export
int gpio_export(char * ver)
{
int fd;
fd = open("/sys/class/gpio/export", O_WRONLY); // write only
if (fd < 0) {
perror("gpio/export");
return fd;
}
write(fd, ver ,sizeof(ver));
close(fd);
return 0;
}
// eg: ver=138
// echo 138 > /sys/class/gpio/unexport
int gpio_unexport(char * ver)
{
int fd;
fd = open("/sys/class/gpio/unexport", O_WRONLY); // write only
if (fd < 0) {
perror("gpio/uexport");
return fd;
}
write(fd, ver ,sizeof(ver));
close(fd);
return 0;
}
/**
* echo out > /sys/class/gpio/pioE10/direction
* str : pioE10,...
* 0 : sucess
* other: err
*/
int gpio_set_dir(char* str)
{
int fd;
int len;
char buf[MAX_BUF];
len = snprintf(buf,sizeof buf,"/sys/class/gpio/%s/direction", str);
printf("str=%s,buf=%s\n",str,buf);
fd = open(buf, O_WRONLY); // write only
if (fd < 0) {
perror("gpio/direction");
return fd;
}
write(fd, "out", sizeof("out"));
close(fd);
return 0;
}
/**
* echo 1 > /sys/class/gpio/pioE10/value
* str : "pioE10", ...
* value : "1","0"
*/
int gpio_set_value(char *str, unsigned int value)
{
int fd;
int len;
char buf[MAX_BUF];
len = snprintf(buf,sizeof buf,"/sys/class/gpio/%s/value", str);
// printf("buf=%s\n",buf);
fd = open(buf, O_RDWR);
if (fd < 0) {
perror("gpio/set_value");
return fd;
}
if(value)
write(fd, "1", sizeof("1"));
else
write(fd, "0", sizeof("0"));
close(fd);
return 0;
}
/**
* str : pioE10...
* bool : 1,0
* gpio_flash("pioE10");
*/
int gpio_flash(char* str)
{
int count = 10;
gpio_set_dir(str); // echo out > /sys/class/gpio/pioE10/direction
while(count--) {
gpio_set_value(str, 1); // echo 1 > /sys/class/gpio/pioE10/value
usleep(1000000);
gpio_set_value(str, 0); // echo 0 > /sys/class/gpio/pioE10/value
usleep(1000000);
}
return 0;
}