gpio_demo.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <fcntl.h>

/****************************************************************
* Constants
****************************************************************/

#define SYSFS_GPIO_DIR "/sys/class/gpio"
#define POLL_TIMEOUT (3 * 1000) /* 3 seconds */
#define MAX_BUF 64

/****************************************************************
 * gpio_export
 ****************************************************************/
int gpio_export(unsigned int gpio)
{
    int fd, len;
    char buf[MAX_BUF];

    fd = open(SYSFS_GPIO_DIR "/export", O_WRONLY);
    if (fd < 0)
    {
        perror("gpio/export");
        return fd;
    }

    len = snprintf(buf, sizeof(buf), "%d", gpio);
    write(fd, buf, len);
    close(fd);

    return 0;
}

/****************************************************************
 * gpio_unexport
 ****************************************************************/
int gpio_unexport(unsigned int gpio)
{
    int fd, len;
    char buf[MAX_BUF];

    fd = open(SYSFS_GPIO_DIR "/unexport", O_WRONLY);
    if (fd < 0)
    {
        perror("gpio/export");
        return fd;
    }

    len = snprintf(buf, sizeof(buf), "%d", gpio);
    write(fd, buf, len);
    close(fd);
    return 0;
}

/****************************************************************
 * gpio_set_dir
 ****************************************************************/
int gpio_set_dir(unsigned int gpio, unsigned int out_flag)
{
    int fd, len;
    char buf[MAX_BUF];

    len = snprintf(buf, sizeof(buf), SYSFS_GPIO_DIR  "/gpio%d/direction", gpio);

    fd = open(buf, O_WRONLY);
    if (fd < 0)
    {
        perror("gpio/direction");
        return fd;
    }

    if (out_flag)
        write(fd, "out", 4);
    else
        write(fd, "in", 3);

    close(fd);
    return 0;
}

/****************************************************************
 * gpio_set_value
 ****************************************************************/
int gpio_set_value(unsigned int gpio, unsigned int value)
{
    int fd, len;
    char buf[MAX_BUF];

    len = snprintf(buf, sizeof(buf), SYSFS_GPIO_DIR "/gpio%d/value", gpio);

    fd = open(buf, O_WRONLY);
    if (fd < 0)
    {
        perror("gpio/set-value");
        return fd;
    }

    if (value)
        write(fd, "1", 2);
    else
        write(fd, "0", 2);

    close(fd);
    return 0;
}

/****************************************************************
 * gpio_get_value
 ****************************************************************/
int gpio_get_value(unsigned int gpio, unsigned int *value)
{
    int fd, len;
    char buf[MAX_BUF];
    char ch;

    len = snprintf(buf, sizeof(buf), SYSFS_GPIO_DIR "/gpio%d/value", gpio);

    fd = open(buf, O_RDONLY);
    if (fd < 0)
    {
        perror("gpio/get-value");
        return fd;
    }

    read(fd, &ch, 1);

    if (ch != '0')
    {
        *value = 1;
    }
    else
    {
        *value = 0;
    }

    close(fd);
    return 0;
}


/****************************************************************
 * gpio_set_edge
 ****************************************************************/

int gpio_set_edge(unsigned int gpio, char *edge)
{
    int fd, len;
    char buf[MAX_BUF];

    len = snprintf(buf, sizeof(buf), SYSFS_GPIO_DIR "/gpio%d/edge", gpio);

    fd = open(buf, O_WRONLY);
    if (fd < 0)
    {
        perror("gpio/set-edge");
        return fd;
    }

    write(fd, edge, strlen(edge) + 1);
    close(fd);
    return 0;
}

/****************************************************************
 * gpio_fd_open
 ****************************************************************/

int gpio_fd_open(unsigned int gpio)
{
    int fd, len;
    char buf[MAX_BUF];

    len = snprintf(buf, sizeof(buf), SYSFS_GPIO_DIR "/gpio%d/value", gpio);

    fd = open(buf, O_RDONLY | O_NONBLOCK );
    if (fd < 0)
    {
        perror("gpio/fd_open");
    }
    return fd;
}

/****************************************************************
 * gpio_fd_close
 ****************************************************************/

int gpio_fd_close(int fd)
{
    return close(fd);
}

/****************************************************************
 * Main
 ****************************************************************/
int main(int argc, char **argv)
{
    int gpio_fd;
    unsigned int gpio = 36;

    gpio_export(gpio);
    gpio_set_dir(gpio, 1);
    gpio_fd = gpio_fd_open(gpio);
    gpio_set_value(gpio, 1);

    unsigned int *value;
    gpio_get_value(gpio, value);
    printf("value of gpio %d is %d", gpio, *value);

    gpio_fd_close(gpio_fd);
    return 0;
}