使用BBB的IO口

只看该作者 · 2017-10-9 10:40

使用BBB的IO口

从Terminal直接控制IO口的方法如下：

root@beaglebone:~# cd /sys/class/gpio
root@beaglebone:/sys/class/gpio# ls -l
total 0
--w------- 1 root root 4096 Jan 1 00:00 export
lrwxrwxrwx 1 root root 0 Jan 1 00:00 gpiochip0 -> ../../devices/virtual/gpio/gpiochip0
lrwxrwxrwx 1 root root 0 Jan 1 00:00 gpiochip32 -> ../../devices/virtual/gpio/gpiochip32
lrwxrwxrwx 1 root root 0 Jan 1 00:00 gpiochip64 -> ../../devices/virtual/gpio/gpiochip64
lrwxrwxrwx 1 root root 0 Jan 1 00:00 gpiochip96 -> ../../devices/virtual/gpio/gpiochip96
--w------- 1 root root 4096 Jan 1 00:00 unexport
root@beaglebone:/sys/class/gpio# echo 44 > export
root@beaglebone:/sys/class/gpio# ls -l
total 0
--w------- 1 root root 4096 Jan 1 00:03 export
lrwxrwxrwx 1 root root 0 Jan 1 00:03 gpio44 -> ../../devices/virtual/gpio/gpio44
lrwxrwxrwx 1 root root 0 Jan 1 00:00 gpiochip0 -> ../../devices/virtual/gpio/gpiochip0
lrwxrwxrwx 1 root root 0 Jan 1 00:00 gpiochip32 -> ../../devices/virtual/gpio/gpiochip32
lrwxrwxrwx 1 root root 0 Jan 1 00:00 gpiochip64 -> ../../devices/virtual/gpio/gpiochip64
lrwxrwxrwx 1 root root 0 Jan 1 00:00 gpiochip96 -> ../../devices/virtual/gpio/gpiochip96
--w------- 1 root root 4096 Jan 1 00:00 unexport
root@beaglebone:/sys/class/gpio# cd gpio44
root@beaglebone:/sys/class/gpio/gpio44# ls -l
total 0
-rw-r--r-- 1 root root 4096 Jan 1 00:03 active_low
-rw-r--r-- 1 root root 4096 Jan 1 00:03 direction
-rw-r--r-- 1 root root 4096 Jan 1 00:03 edge
drwxr-xr-x 2 root root 0 Jan 1 00:03 power
lrwxrwxrwx 1 root root 0 Jan 1 00:03 subsystem -> ../../../../class/gpio
-rw-r--r-- 1 root root 4096 Jan 1 00:03 uevent
-rw-r--r-- 1 root root 4096 Jan 1 00:03 value
root@beaglebone:/sys/class/gpio/gpio44# cat direction
in
root@beaglebone:/sys/class/gpio/gpio44# echo out > direction
root@beaglebone:/sys/class/gpio/gpio44# cat direction
out
root@beaglebone:/sys/class/gpio/gpio44# cat value
0
root@beaglebone:/sys/class/gpio/gpio44# echo 1 > value
root@beaglebone:/sys/class/gpio/gpio44# cat value
1

复制代码
解释一下，首先要把某个（本例中是第44个，即P8_12）gpio export一下，变成用户可用的状态，然后目录里就会多出来一个gpio44目录，进入它对相应文件进行读写就可以操作io口了。输入输出是一样的道理。读的话Linux会自动实时更新value文件里的数据，但更新速度有多快暂时还不清楚，高速io操作的话用这种方法感觉不靠谱。不过速度不敏感的话是没问题的。用c程序控制io口，我们当然可以完全照搬上面对文件操作的过程，只不过写成c语言的形式。具体如下：

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <fcntl.h> //define O_WRONLY and O_RDONLY
#define SYSFS_GPIO_DIR "/sys/class/gpio"
#define MAX_BUF 64
void main()
{
int fd, len;
char buf[MAX_BUF];
char ch;
int i;
//export gpio44
fd = open(SYSFS_GPIO_DIR "/export", O_WRONLY);
len = snprintf(buf,sizeof(buf),"44");
write(fd,buf,len);
close(fd);
//set direction
snprintf(buf,sizeof(buf),SYSFS_GPIO_DIR"/gpio44/direction");
fd = open(buf, O_WRONLY);
write(fd, "in", 3);
close(fd);
//read and print value 10 times
for(i=0;i<10;i++)
{
snprintf(buf,sizeof(buf),SYSFS_GPIO_DIR"/gpio44/value");
fd = open(buf, O_RDONLY);
read(fd,&ch,1);
printf("%c\n",ch);
close(fd);
usleep(1000000);
}
}

复制代码

这个例子实现了把gpio44引脚设置为输入引脚，然后每秒检测一次输入电平，并将电平（0或1）打印在终端上。

使用BBB的IO口

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