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。
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