嵌入式linux文件io方式操作gpio口示例

嵌入式linux文件io方式操作gpio口示例

在嵌入式linux中应用层操作gpio口，如果懒得写驱动或者懒得翻寄存器手册，有一种简单的方式操作，只需要终端申请io，然后设置方向就可以直接操作,这里以野火的imx板子为例示范，后面以一个led闪烁灯程序作为例子

一、命令行操作示范
1.确认文件系统根目录里面有sys目录，没有的话需要在内核编译的时候打开Device Drivers —> GPIO Support —> /sys/class/gpio/… (sysfs interface)

2.查看计算申请的编号，这里我们以IO1.1为例

root@npi:/sys/class/gpio# cat gpiochip0/label
209c000.gpio
这里基地址是209c000 ，在imx6ullrm手册里面P1141里，GPIO memory map查到就是GPIO1
root@npi:/sys/class/gpio# cat gpiochip0/base
0
我们要申请的是IO1.1，0+1=1

2.申请io
在/sys/class/gpio目录下，命令终端输入echo 1 > export，会在当前目录下产生一个gpio1的目录
root@npi:/sys/class/gpio# echo 1 > export

3.设置输出
进入gpio1目录，修改direction
root@npi:/sys/class/gpio/gpio1# echo out > direction

4.设置电平
进入gpio1目录，修改value
root@npi:/sys/class/gpio/gpio1# echo 0 > value

5.配置输入
root@npi:/sys/class/gpio/gpio1# echo in > direction

6.读取电平
root@npi:/sys/class/gpio/gpio1# cat value
0
附：active_low device direction edge power subsystem uevent value
active_low：中断配置 低电平有效 高电平有效
edge：中断配置 ，上升沿 下降沿
uevent：中断事件

二、c程序操作

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

int led_init()
{
    
    
	#defien led "1"
	#define led_path "/sys/class/gpio/gpio1"
	#define led_dir "/sys/class/gpio/gpio1/direction"
	//申请io
	int fd = 0;
	fd = open("/sys/class/gpio/export", O_WRONLY);
    if(-1 == fd)
    {
    
    
       printf("[%s]:[%d] open gpio export file error\r\n", __FUNCTION__, __LINE__);
       exit(1);
	}
	if(-1 == write(fd, led, 1))
    {
    
    
        printf("write file operation error\r\n");
        exit(1);
    }
    close(fd);
	//配置
	fd = open(led_dir, O_WRONLY);
    if(-1 == fd)
    {
    
    
       printf("[%s]:[%d] open gpio direction file error\r\n", __FUNCTION__, __LINE__);       
       exit(1);
    }
    if(-1 == write(fd, "in", sizeof("in")))
    {
    
    
       printf("[%s]:[%d] write operation direction error\r\n", __FUNCTION__, __LINE__);
       close(direction_fd);
       exit(1);
    }
    close(fd);
	
	return 0;
}

int led_ctrl(unsigned char x)
{
    
    
	#define led_value "/sys/class/gpio/gpio1/value"
	int fd = 0;
	
	fd = open(led_value, O_WRONLY);
	if(-1 == fd)
    {
    
    
       printf("[%s]:[%d] open gpio export file error\r\n", __FUNCTION__, __LINE__);
       exit(1);
	}
	if(x)
	{
    
    
		if(-1 == write(fd, "1", sizeof("in")))
		{
    
    
		   printf("[%s]:[%d] write operation value error\r\n", __FUNCTION__, __LINE__);
		   close(direction_fd);
		   exit(1);
		}
	}
	else
	{
    
    
		if(-1 == write(fd, "0", sizeof("in")))
		{
    
    
		   printf("[%s]:[%d] write operation value error\r\n", __FUNCTION__, __LINE__);
		   close(direction_fd);
		   exit(1);
		}
	}
	
	return 0;
}

int read_ledstate()
{
    
    
	#define led_value "/sys/class/gpio/gpio1/value"
	int fd = 0;
	char value;
	
	fd = open(led_value, O_WRONLY);
	if(-1 == fd)
    {
    
    
       printf("[%s]:[%d] open gpio export file error\r\n", __FUNCTION__, __LINE__);
       exit(1);
	}
	if(-1 == read(gpiovalue_fd, &value, sizeof(value)))
    {
    
    
        printf("[%s]:[%d] read gpiovalue is fail\r\n", __FUNCTION__, __LINE__);
        close(gpiovalue_fd);
        exit(1);
    }
	
	return value;
}

int main()
{
    
    
	int x = 0;
	
	led_init();
	led_ctrl(1);
	x = read_ledstate();
	printf("led state = %d \r\n", x);
	
	return 0;
}