contiki/lib/timer.c

/**
 * \defgroup timer Timer library
 * @{
 *
 * The Contiki kernel does not provide support for timed
 * events. Rather, an application that wants to use timers needs to
 * explicitly use the timer library.
 *
 * The timer library provides functions for setting, resetting and
 * restarting timers, and for checking if a timer has expired. An
 * application must "manually" check if its timers have expired; this
 * is not done automatically.
 *
 * A timer is declared as a \c struct \c timer and all access to the
 * timer is made by a pointer to the declared timer.
 *
 * Example:
 \code

 static struct timer periodic;

 LOADER_INIT_FUNC(example_init, arg) {
   timer_set(&periodic, CLOCK_SECOND);
 }
 
 EK_POLLHANDLER(pollhandler) {
   if(timer_expired(&periodic)) {
     timer_restart(&periodic);
     do_periodic_stuff();
   }
 }
 
 \endcode
 *
 * \note The timer library uses the \ref clock "Clock library" to
 * measure time. Intervals should be specified in the format used by
 * the clock library.
 *
 * \sa \ref clock "Clock library"
 */

/**
 * \file
 * Timer library implementation.
 * \author
 * Adam Dunkels <adam@sics.se>
 */

/*
 * Copyright (c) 2004, Swedish Institute of Computer Science.
 * 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. Neither the name of the Institute 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 THE INSTITUTE AND CONTRIBUTORS ``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 THE INSTITUTE OR CONTRIBUTORS 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. 
 *
 * This file is part of the Contiki operating system.
 * 
 * Author: Adam Dunkels <adam@sics.se>
 *
 * $Id: timer.c,v 1.5 2005/02/07 22:45:14 adamdunkels Exp $
 */
#include "timer.h"

/*---------------------------------------------------------------------------*/
/**
 * Set a timer.
 *
 * This function is used to set a timer for a time sometime in the
 * future. The function timer_expired() will evaluate to true after
 * the timer has expired.
 *
 * \param t A pointer to the timer
 * \param interval The interval before the timer expires.
 *
 */
void
timer_set(struct timer *t, clock_time_t interval)
{
  t->interval = interval;
  t->start = clock_time();
}
/*---------------------------------------------------------------------------*/
/**
 * Reset the timer with the same interval.
 *
 * This function resets the timer with the same interval that was
 * given to the timer_set() function. The start point of the interval
 * is the exact time that the timer last expired. Therefore, this
 * function will cause the timer to be stable over time, unlike the
 * timer_rester() function.
 *
 * \param t A pointer to the timer.
 *
 * \sa timer_restart()
 */
void
timer_reset(struct timer *t)
{
  t->start += t->interval;
}
/*---------------------------------------------------------------------------*/
/**
 * Restart the timer from the current point in time
 *
 * This function restarts a timer with the same interval that was
 * given to the timer_set() function. The timer will start at the
 * current time.
 *
 * \note A periodic timer will drift if this function is used to reset
 * it. For preioric timers, use the timer_reset() function instead.
 *
 * \param t A pointer to the timer.
 *
 * \sa timer_reset()
 */
void
timer_restart(struct timer *t)
{
  t->start = clock_time();
}
/*---------------------------------------------------------------------------*/
/**
 * Check if a timer has expired.
 *
 * This function tests if a timer has expired and returns true or
 * false depending on its status.
 *
 * \param t A pointer to the timer
 *
 * \return Non-zero if the timer has expired, zero otherwise.
 *
 */
int
timer_expired(struct timer *t)
{
  return (clock_time_t)(clock_time() - t->start) >= (clock_time_t)t->interval;
}
/*---------------------------------------------------------------------------*/