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Linux下用文件IO的方式操作GPIO(/sys/class/gpio)

(2015-11-26 16:14:16)
标签:

linux

gpio

分类: Linux

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directionvalue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openclosereadwrite

 

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

  /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, lowhigh/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10

 

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,不是中断引脚

// 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;

}  

参考文档:

http://blog.csdn.net/xukai871105/article/details/38456079

http://blog.csdn.net/sukhoi27smk/article/details/26447765

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