A C program that listens for button presses on a Beaglebone GPIO pin and reports the press duration.

gpio.c

/**
 * Title:   gpio.c
 *
 * Author:  Andrew Montag
 *          ajmontag@gmail.com
 *          sites.google.com/site/andrewmontag
 *
 * Licence: Boost Software Licence - Verison 1.0
 *          http://www.boost.org/users/license.html
 *
 * Purpose:
 * Helpers for configuring and accessing GPIO pins.
 */

/**
 * Original source from
 *  https://www.ridgerun.com/developer/wiki/index.php/Gpio-int-test.c
 * as example code.
 * Modularized by Andrew Montag, 10/30/2012
 *
 * 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 "gpio.h"

#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 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];

    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;
    }

    gpio_get_value_fd(fd, value);

    close(fd);
    return 0;
}

int gpio_get_value_fd(int fd, unsigned int *value)
{
    char ch;

    read(fd, &ch, 1);

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

    return 0;
}

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

int gpio_set_edge(unsigned int gpio, const 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);
}

gpio.h

/**
 * Title:   gpio.h
 *
 * Author:  Andrew Montag
 *          ajmontag@gmail.com
 *          sites.google.com/site/andrewmontag
 *
 * Licence: Boost Software Licence - Verison 1.0
 *          http://www.boost.org/users/license.html
 *
 * Purpose:
 * Helpers for configuring and accessing GPIO pins.
 */

#ifndef _GPIO_H_
#define _GPIO_H_

/**
 * @ return 0 on success
 *
 * @param gpio the gpio pin number.
 *  If the pin is GPIOm_n, then the pin number is
 *  m * 32 + n. Example: GPIO3_21 = 3*32+21 = 117
 */

/**
 * gpio_export
 * export a gpio pin for use in the user space.
 * must be called before the pin can be used.
 */
int gpio_export(unsigned int gpio);


/**
 * gpio_unexport
 * undo the export action.
 */
int gpio_unexport(unsigned int gpio);

#define GPIO_DIR_INPUT  (0)
#define GPIO_DIR_OUTPUT (1)

/**
 * gpio_set_dir
 * @param out_flag true=output, false=input
 */
int gpio_set_dir(unsigned int gpio, unsigned int out_flag);


/**
 * gpio_set_value
 * writes the boolean value to the pin.
 */
int gpio_set_value(unsigned int gpio, unsigned int value);


/**
 * gpio_get_value
 * reads the state of the pin.
 * @param as return, 0 or 1
 */
int gpio_get_value(unsigned int gpio, unsigned int *value);

/** @param fd an fd opened using gpio_fd_open */
int gpio_get_value_fd(int fd, unsigned int *value);


static const char* kPollEdge_rising = "rising";
static const char* kPollEdge_falling = "falling";
static const char* kPollEdge_both = "both";

/**
 * gpio_set_edge
 * @param edge should be "rising", "falling", or "both"
 */
int gpio_set_edge(unsigned int gpio, const char *edge);


/**
 * gpio_fd_open
 * @return an open an fd for later use.
 * useful when using poll().
 */
int gpio_fd_open(unsigned int gpio);


/**
 * gpio_fd_close
 * close an open fd.
 */
int gpio_fd_close(int fd);

#endif

press_duration.c

/**
 * Title:   press_duration.c
 *
 * Author:  Andrew Montag
 *          ajmontag@gmail.com
 *          sites.google.com/site/andrewmontag
 *
 * Licence: Boost Software Licence - Verison 1.0
 *          http://www.boost.org/users/license.html
 *
 * Purpose:
 * A program which listens for button presses on a GPIO pin and reports the
 * press duration.
 *
 */

#include "gpio.h"

#include <sys/time.h>
#include <poll.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <assert.h>

#define POLL_TIMEOUT_30_SEC (30 * 1000)
#define POLL_TIMEOUT_20_SEC (20 * 1000)
#define POLL_TIMEOUT_10_SEC (10 * 1000)
#define POLL_TIMEOUT_5_SEC  (5  * 1000)
#define POLL_TIMEOUT_2_SEC  (2  * 1000)
#define POLL_TIMEOUT_1_SEC  (1  * 1000)
#define POLL_TIMEOUT_INF    (-1)

#define MAX_BUF 64

void report_button_ms(int duration) {
    printf("button pressed for %d ms.\n", duration);
}

int main(int argc, char **argv, char **envp)
{
    struct pollfd pollfdset;
    const int nfds = 1;
    int timeout, rc;
    char *buf[MAX_BUF];
    unsigned int gpio;
    int len;

    // gpio pin number
    if (argc < 2) {
        printf("Usage: gpio-int <gpio-pin>\n\n");
        printf("Reports button press duration on a gpio pin\n");
        exit(-1);
    }

    gpio = atoi(argv[1]);

    // export and configure the pin for our usage
    gpio_export(gpio);
    gpio_set_dir(gpio, GPIO_DIR_INPUT);

    // stuff the poll structure
    memset((void*) &pollfdset, 0, sizeof(pollfdset));
    pollfdset.fd = gpio_fd_open(gpio);
    pollfdset.events = POLLPRI;

    // clear any backed up events
    // XXX I'm not sure why we need this, but without it we get a false
    // report of an edge from the first poll()
    rc = poll(&pollfdset, nfds, 0);
    len = read(pollfdset.fd, buf, MAX_BUF);

    while (1) {
        //printf("waiting for rising edge.\n");

        // wait for rising edge, button press
        pollfdset.revents = 0;
        gpio_set_edge(gpio, kPollEdge_rising);
        rc = poll(&pollfdset, nfds, POLL_TIMEOUT_INF);
        len = read(pollfdset.fd, buf, MAX_BUF);

        if (rc < 0) {
            // TODO error
            printf("\npoll() failed!\n");
            return -1;
        } /* else if (rc == 0) timeout */

        if (pollfdset.revents & POLLPRI) {
            // rising edge occurred
            printf("rising edge!\n");

            // make note of the time of the rising edge
            struct timeval starttv;
            gettimeofday(&starttv, NULL);

            // now wait for the falling edge
            gpio_set_edge(gpio, kPollEdge_falling);

            // the button is currently being held down
            int duration = -1;
            while (duration < 0) {
                //printf("waiting for falling edge\n");
                pollfdset.revents = 0;
                rc = poll(&pollfdset, nfds, POLL_TIMEOUT_5_SEC);
                len = read(pollfdset.fd, buf, MAX_BUF);

                if (rc < 0) {
                    printf("error!\n");
                    // TODO error
                    duration = 0;
                } else if (0 == rc) {
                    // timeout, check the state of the button to make sure we didn't miss the edge
                    printf("timeout while waiting for falling edge\n");

                    unsigned int value = 0xFFFF;
                    rc = gpio_get_value_fd(pollfdset.fd, &value);
                    if (0 == value) {
                        // button is released, but we missed the falling edge
                        // report a very short duration
                        printf("Button falling edge missed!\n"); // debug only
                        duration = 1;
                    } else if (1 == value) {
                        // the button is still pressed, carry on
                        printf("Button still pressed\n");
                    }

                    if (rc < 0) {
                        printf("error2!");
                        // TODO error
                        duration = 0;
                    }
                }

                if (pollfdset.revents & POLLPRI) {
                    // falling edge occurred
                    printf("falling edge!\n");

                    // make note of the falling edge time
                    struct timeval endtv;
                    gettimeofday(&endtv, NULL);

                    // subtract the times and convert millisecond
                    struct timeval difftv;
                    timersub(&endtv, &starttv, &difftv);
                    duration = (difftv.tv_sec) * 1000 + (difftv.tv_usec) / 1000 ;
                    assert(duration >= 0); // XXX assert?
                }
            } // end while duration < 0

            report_button_ms(duration);

        }

    }

    // TODO unexport and put in the SIGTERM handler
    gpio_fd_close(pollfdset.fd);
    return 0;
}

Many thanks to Derek Molloy and his YouTube video

Note: I have this running under Ubuntu 12.04 on the beaglebone.