[sysfs]Linux GPIO简单使用方式

/* Copyright (c) 2011, RidgeRun 
 * All rights reserved. 
 *  
 * Redistribution and use in source and binary forms, with or without 
 * modification, are permitted provided that the following conditions are met: 
 * 1. Redistributions of source code must retain the above copyright 
 *    notice, this list of conditions and the following disclaimer. 
 * 2. Redistributions in binary form must reproduce the above copyright 
 *    notice, this list of conditions and the following disclaimer in the 
 *    documentation and/or other materials provided with the distribution. 
 * 3. All advertising materials mentioning features or use of this software 
 *    must display the following acknowledgement: 
 *    This product includes software developed by the RidgeRun. 
 * 4. Neither the name of the RidgeRun nor the 
 *    names of its contributors may be used to endorse or promote products 
 *    derived from this software without specific prior written permission. 
 *  
 * THIS SOFTWARE IS PROVIDED BY RIDGERUN ‘‘AS IS‘‘ AND ANY 
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 
 * DISCLAIMED. IN NO EVENT SHALL RIDGERUN BE LIABLE FOR ANY 
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND 
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS 
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
 */  
  
#include <stdio.h>  
#include <stdlib.h>  
#include <string.h>  
#include <errno.h>  
#include <unistd.h>  
#include <fcntl.h>  
#include <poll.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, char **envp)  
{  
    struct pollfd fdset[2];  
    int nfds = 2;  
    int gpio_fd, timeout, rc;  
    char *buf[MAX_BUF];  
    unsigned int gpio;  
    int len;  
  
  
  
    if (argc < 2) {  
        printf("Usage: gpio-int <gpio-pin>\n\n");  
        printf("Waits for a change in the GPIO pin voltage level or input on stdin\n");  
        exit(-1);  
    }  
  
    gpio = atoi(argv[1]);  
  
    gpio_export(gpio);  
    gpio_set_dir(gpio, 0);  
    gpio_set_edge(gpio, "rising");  
    gpio_fd = gpio_fd_open(gpio);  
  
    timeout = POLL_TIMEOUT;  
   
    while (1) {  
        memset((void*)fdset, 0, sizeof(fdset));  
  
        fdset[0].fd = STDIN_FILENO;  
        fdset[0].events = POLLIN;  
        
        fdset[1].fd = gpio_fd;  
        fdset[1].events = POLLPRI;  
  
        rc = poll(fdset, nfds, timeout);        
  
        if (rc < 0) {  
            printf("\npoll() failed!\n");  
            return -1;  
        }  
        
        if (rc == 0) {  
            printf(".");  
        }  
              
        if (fdset[1].revents & POLLPRI) {  
            len = read(fdset[1].fd, buf, MAX_BUF);  
            printf("\npoll() GPIO %d interrupt occurred\n", gpio);  
        }  
  
        if (fdset[0].revents & POLLIN) {  
            (void)read(fdset[0].fd, buf, 1);  
            printf("\npoll() stdin read 0x%2.2X\n", (unsigned int) buf[0]);  
        }  
  
        fflush(stdout);  
    }  
  
    gpio_fd_close(gpio_fd);  
    return 0;  
}