/*
 based largely on code from http://www.semicomplete.com/blog/geekery/soekris-gpio.html
 which did the same thing on a Soerkis box.
*/

// the GPIO0 pins for the three LEDs on the Alix 2c3 (left-to-right)
#define ALIX_LED_0 6
#define ALIX_LED_1 25
#define ALIX_LED_2 27

// config parameters for this program
#define LED_TO_PULSE ALIX_LED_2 // we're just going to do the right-most LED
#define PULSE_LENGTH 10000 // in microseconds
#define PULSE_STEP 100 // in microseconds

// rest of source code stuff
#define _BSD_SOURCE
#include <sys/types.h>
#include <sys/gpio.h>
#include <sys/ioctl.h>
#include <sys/select.h>
#include <sys/time.h>
#include <err.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#define _PATH_DEV_GPIO	"/dev/gpio0"

#define DURATION(a, b) ((b.tv_sec - a.tv_sec) * 1000000) + (b.tv_usec - a.tv_usec)
#define ON 1
#define OFF 0

char *device = _PATH_DEV_GPIO;
int devfd = -1;

void led(u_int pin, int state) {
  /* based on code at OpenBSD/src/usr.sbin/gpioctl/gpioctl.c,
     from which the following notice is taken:
     
/*	$OpenBSD: gpioctl.c,v 1.4 2005/11/17 10:18:18 grange Exp $
 *
 * Copyright (c) 2004 Alexander Yurchenko <grange@openbsd.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.

  */
  struct gpio_pin_op op;

  if (state < 0 || state > 2)
      errx(1, "%d: invalid value", state);

  bzero(&op, sizeof(op));
  op.gp_pin = pin;
  op.gp_value = (state == 0 ? GPIO_PIN_LOW : GPIO_PIN_HIGH);
  if (state < 2) {
      if (ioctl(devfd, GPIOPINWRITE, &op) == -1)
          err(1, "GPIOPINWRITE");
  } else {
      if (ioctl(devfd, GPIOPINTOGGLE, &op) == -1)
          err(1, "GPIOPINTOGGLE");
  }

}

/* usleep(3) and select(2) are unreliable. Let's spin wait instead */
void waittime(long duration) {
  struct timeval start;
  struct timeval now;
  gettimeofday(&start, NULL);

  for (gettimeofday(&now, NULL); DURATION(start, now) < duration; gettimeofday(&now, NULL)) ;
}

int main() {
  int fd;
  int state = ON;
	if ((devfd = open(device, O_RDWR)) == -1)
		err(1, "%s", device);

  int count = 0;
  int interval = PULSE_LENGTH;
  int duty_cycle = 0; // duty cycle is how long the 'on' state should be.
                      // Same units as interval (microseconds)

  int dir = 1;
  
  for (count = 0; count <= (2 * PULSE_LENGTH / PULSE_STEP); count++) {
    duty_cycle += PULSE_STEP * dir;

    if (duty_cycle >= interval) {
      duty_cycle = interval;
      dir = -1;
    } 
    if (duty_cycle <= 0) {
      duty_cycle = 0;
      dir = 1;
    }

    state = ON;
    led(LED_TO_PULSE, state);
    waittime(duty_cycle);

    state = OFF;
    led(LED_TO_PULSE, state);
    waittime(interval - duty_cycle);
  }

  return 0;
}