event.c

/*
 * Copyright (c) 2007-21, Kalopa Robotics Limited.  All rights reserved.
 *
 * This is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.  It is distributed in the hope that it will be
 * useful, but WITHOUT ANY WARRANTY; without even the implied warranty
 * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this product; see the file COPYING.  If not, write to the
 * Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 * ABSTRACT
 * My version of a lightweight timer event machine.
 */
#include <stdio.h>
#include <stdlib.h>
#include <avr/io.h>

#include "libavr.h"

volatile uchar_t	tick_count = 0;
struct	thread		*thead = NULL;

/*
 * Register a timer callback.
 */
int
timer_callback(unsigned int (*func)(), int tick)
{
	struct thread *tp;

	if ((tp = (struct thread *)malloc(sizeof(struct thread))) == NULL)
		return(-1);
	tp->func = func;
	tp->tick = tick;
	timer_enqueue(tp);
	return(0);
}

/*
 * Enqueue a callback on the appropriate timer queue. The queue is
 * ordered by the relative number of milliseconds between each callback.
 */
void
timer_enqueue(struct thread *tp)
{
	struct thread *ntp;

	if (thead == NULL || thead->tick > tp->tick) {
		/*
		 * Insert at the front.
		 */
		tp->next = thead;
		thead = tp;
	} else {
		for (ntp = thead; ntp->next != NULL; ntp = ntp->next) {
			if (ntp->next->tick > tp->tick)
				break;
		}
		tp->next = ntp->next;
		ntp->next = tp;
	}
	if (tp->next != NULL)
		tp->next->tick -= tp->tick;
}

/*
 * Loop through the timer list, dealing with each timer tick.
 */
void
timer_loop()
{
	struct thread *tp;

	/*
	 * Only run the linked-list if the timer has fired.
	 */
	for (; tick_count > 0; tick_count--) {
		if (thead != NULL && thead->tick > 0)
			thead->tick--;
		while ((tp = thead) != NULL && tp->tick == 0) {
			thead = tp->next;
			if ((tp->tick = tp->func()) > 0)
				timer_enqueue(tp);
			else
				free((char *)tp);
		}
	}
}

/*
 * Ping the timer loop - time has moved on. Called from the Interrupt
 * Service Routine.  Generally a tick happens every 5ms, which is the
 * unit of measure for the event queue.
 */
void
timer_tick()
{
	tick_count++;
}