Linux下用文件IO的方式操作GPIO（/sys/class/gpio）(转)

通过sysfs方式控制GPIO，先访问/sys/class/gpio目录，向export文件写入GPIO编号，使得该GPIO的操作接口从内核空间暴露到用户空间，GPIO的操作接口包括direction和value等，direction控制GPIO方向，而value可控制GPIO输出或获得GPIO输入。文件IO方式操作GPIO，使用到了4个函数open、close、read、write。

首先，看看系统中有没有“/sys/class/gpio”这个文件夹。如果没有请在编译内核的时候加入  Device Drivers-> GPIO Support ->/sys/class/gpio/… (sysfs interface)。

/sys/class/gpio 的使用说明：

gpio_operation 通过/sys/文件接口操作IO端口 GPIO到文件系统的映射

◇  控制GPIO的目录位于/sys/class/gpio

◇  /sys/class/gpio/export文件用于通知系统需要导出控制的GPIO引脚编号

◇  /sys/class/gpio/unexport 用于通知系统取消导出

◇  /sys/class/gpio/gpiochipX目录保存系统中GPIO寄存器的信息，包括每个寄存器控制引脚的起始编号base，寄存器名称，引脚总数 导出一个引脚的操作步骤

◇  首先计算此引脚编号，引脚编号 = 控制引脚的寄存器基数 + 控制引脚寄存器位数

◇  向/sys/class/gpio/export写入此编号，比如12号引脚，在shell中可以通过以下命令实现，命令成功后生成/sys/class/gpio/gpio12目录，如果没有出现相应的目录，说明此引脚不可导出

◇  direction文件，定义输入输入方向，可以通过下面命令定义为输出。direction接受的参数：in, out, high, low。high/low同时设置方向为输出，并将value设置为相应的1/0

◇  value文件是端口的数值，为1或0

几个例子：

1. 导出

/sys/class/gpio# echo 44 > export

2. 设置方向

/sys/class/gpio/gpio44# echo out > direction

3. 查看方向

/sys/class/gpio/gpio44# cat direction

4. 设置输出

/sys/class/gpio/gpio44# echo 1 > value

5. 查看输出值

/sys/class/gpio/gpio44# cat value

6. 取消导出

/sys/class/gpio# echo 44 > unexport

文件读写例程：

#include stdlib.h

#include stdio.h

#include string.h

#include unistd.h

#include fcntl.h  //define O_WRONLY and O_RDONLY

//芯片复位引脚: P1_16

#define SYSFS_GPIO_EXPORT          "/sys/class/gpio/export"

#define SYSFS_GPIO_RST_PIN_VAL      "48"

#define SYSFS_GPIO_RST_DIR          "/sys/class/gpio/gpio48/direction"

#define SYSFS_GPIO_RST_DIR_VAL      "OUT"

#define SYSFS_GPIO_RST_VAL          "/sys/class/gpio/gpio48/value"

#define SYSFS_GPIO_RST_VAL_H        "1"

#define SYSFS_GPIO_RST_VAL_L        "0"

int main()

{

int fd;

//打开端口/sys/class/gpio# echo 48 > export

fd = open(SYSFS_GPIO_EXPORT, O_WRONLY);

if(fd == -1)

{

printf("ERR: Radio hard reset pin open error.\n");

return EXIT_FAILURE;

}

write(fd, SYSFS_GPIO_RST_PIN_VAL ,sizeof(SYSFS_GPIO_RST_PIN_VAL));

close(fd);

//设置端口方向/sys/class/gpio/gpio48# echo out > direction

fd = open(SYSFS_GPIO_RST_DIR, O_WRONLY);

if(fd == -1)

{

printf("ERR: Radio hard reset pin direction open error.\n");

return EXIT_FAILURE;

}

write(fd, SYSFS_GPIO_RST_DIR_VAL, sizeof(SYSFS_GPIO_RST_DIR_VAL));

close(fd);

//输出复位信号: 拉高>100ns

fd = open(SYSFS_GPIO_RST_VAL, O_RDWR);

if(fd == -1)

{

printf("ERR: Radio hard reset pin value open error.\n");

return EXIT_FAILURE;

}

while(1)

{

write(fd, SYSFS_GPIO_RST_VAL_H, sizeof(SYSFS_GPIO_RST_VAL_H));

usleep(1000000);

write(fd, SYSFS_GPIO_RST_VAL_L, sizeof(SYSFS_GPIO_RST_VAL_L));

usleep(1000000);

}

close(fd);

printf("INFO: Radio hard reset pin value open error.\n");

return 0;

}

另外参考网上一个网友的程序，这里做了验证，并实现中断检测函数。如下：

#include stdlib.h

#include stdio.h

#include string.h

#include unistd.h

#include fcntl.h

#include poll.h

#define MSG(args...) printf(args)

//函数声明

static int gpio_export(int pin);

static int gpio_unexport(int pin);

static int gpio_direction(int pin, int dir);

static int gpio_write(int pin, int value);

static int gpio_read(int pin);

static int gpio_export(int pin)

{

char buffer[64];

int len;

int fd;

fd = open("/sys/class/gpio/export", O_WRONLY);

if (fd < 0) {

MSG("Failed to open export for writing!\n");

return(-1);

}

len = snprintf(buffer, sizeof(buffer), "%d", pin);

if (write(fd, buffer, len) < 0) {

MSG("Failed to export gpio!");

return -1;

}

close(fd);

return 0;

}

static int gpio_unexport(int pin)

{

char buffer[64];

int len;

int fd;

fd = open("/sys/class/gpio/unexport", O_WRONLY);

if (fd < 0) {

MSG("Failed to open unexport for writing!\n");

return -1;

}

len = snprintf(buffer, sizeof(buffer), "%d", pin);

if (write(fd, buffer, len) < 0) {

MSG("Failed to unexport gpio!");

return -1;

}

close(fd);

return 0;

}

//dir: 0-->IN, 1-->OUT

static int gpio_direction(int pin, int dir)

{

static const char dir_str[] = "in\0out";

char path[64];

int fd;

snprintf(path, sizeof(path), "/sys/class/gpio/gpio%d/direction", pin);

fd = open(path, O_WRONLY);

if (fd < 0) {

MSG("Failed to open gpio direction for writing!\n");

return -1;

}

if (write(fd, &dir_str[dir == 0 ? 0 : 3], dir == 0 ? 2 : 3) < 0) {

MSG("Failed to set direction!\n");

return -1;

}

close(fd);

return 0;

}

//value: 0-->LOW, 1-->HIGH

static int gpio_write(int pin, int value)

{

static const char values_str[] = "01";

char path[64];

int fd;

snprintf(path, sizeof(path), "/sys/class/gpio/gpio%d/value", pin);

fd = open(path, O_WRONLY);

if (fd < 0) {

MSG("Failed to open gpio value for writing!\n");

return -1;

}

if (write(fd, &values_str[value == 0 ? 0 : 1], 1) < 0) {

MSG("Failed to write value!\n");

return -1;

}

close(fd);

return 0;

}

static int gpio_read(int pin)

{

char path[64];

char value_str[3];

int fd;

snprintf(path, sizeof(path), "/sys/class/gpio/gpio%d/value", pin);

fd = open(path, O_RDONLY);

if (fd < 0) {

MSG("Failed to open gpio value for reading!\n");

return -1;

}

if (read(fd, value_str, 3) < 0) {

MSG("Failed to read value!\n");

return -1;

}

close(fd);

return (atoi(value_str));

}

// none表示引脚为输入，��是中断引脚

// rising表示引脚为中断输入，上升沿触发

// falling表示引脚为中断输入，下降沿触发

// both表示引脚为中断输入，边沿触发

// 0-->none, 1-->rising, 2-->falling, 3-->both

static int gpio_edge(int pin, int edge)

{

const char dir_str[] = "none\0rising\0falling\0both";

char ptr;

char path[64];

int fd;

switch(edge){

case 0:

ptr = 0;

break;

case 1:

ptr = 5;

break;

case 2:

ptr = 12;

break;

case 3:

ptr = 20;

break;

default:

ptr = 0;

}

snprintf(path, sizeof(path), "/sys/class/gpio/gpio%d/edge", pin);

fd = open(path, O_WRONLY);

if (fd < 0) {

MSG("Failed to open gpio edge for writing!\n");

return -1;

}

if (write(fd, &dir_str[ptr], strlen(&dir_str[ptr])) < 0) {

MSG("Failed to set edge!\n");

return -1;

}

close(fd);

return 0;

}

//GPIO1_17

int main()

{

int gpio_fd, ret;

struct pollfd fds[1];

char buff[10];

unsigned char cnt = 0;

//LED引脚初始化

gpio_export(115);

gpio_direction(115, 1);

gpio_write(115, 0);

//按键引脚初始化

gpio_export(49);

gpio_direction(49, 0);

gpio_edge(49,1);

gpio_fd = open("/sys/class/gpio/gpio49/value",O_RDONLY);

if(gpio_fd < 0){

MSG("Failed to open value!\n");

return -1;

}

fds[0].fd = gpio_fd;

fds[0].events  = POLLPRI;

ret = read(gpio_fd,buff,10);

if( ret == -1 )

MSG("read\n");

while(1){

ret = poll(fds,1,0);

if( ret == -1 )

MSG("poll\n");

if( fds[0].revents & POLLPRI){

ret = lseek(gpio_fd,0,SEEK_SET);

if( ret == -1 )

MSG("lseek\n");

ret = read(gpio_fd,buff,10);

if( ret == -1 )

MSG("read\n");

gpio_write(115, cnt++%2);

}

usleep(100000);

}

return 0;

}

本文永久更新链接地址：http://www.linuxidc.com/Linux/2016-03/129596.htm