/*
    ChibiOS/RT - Copyright (C) 2006,2007,2008,2009,2010 Giovanni Di Sirio.

    This file is part of ChibiOS/RT.

    ChibiOS/RT 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 3 of the License, or
    (at your option) any later version.

    ChibiOS/RT 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 program.  If not, see <http://www.gnu.org/licenses/>.
*/

/**
 * @page article_timing Reliable timings using Threads
 * One common task is to have threads do something at regular, scheduled,
 * intervals.
 * An obvious solution is to write something like this:
 * @code
msg_t my_thread(void *param) {

  while (TRUE) {
    do_something();
    chThdSleepMilliseconds(1000);   /* Fixed interval */
  }
}
 * @endcode
 * This example works well assuming that @p do_something() execution time is
 * well below the system tick period and that @p my_thread() is not preempted
 * by other threads inserting long intervals.<br>
 * If the above conditions are not satisfied you may have @p do_something()
 * executed at irregular intervals, as example:<br><br>
 * T0...T0+1000...T0+2002...T0+3002...T0+4005...etc.<br><br>
 * Also note that the error increases over time and this kind of behavior can
 * lead to anomalies really hard to debug.
 * <h2>A better solution</h2>
 * It is possible to rewrite the above code using absolute deadlines rather
 * than fixed intervals:
 * @code
msg_t my_thread(void *param) {

  systick_t time = chTimeNow();     /* T0 */
  while (TRUE) {
    time += MS2ST(1000);            /* Next deadline */
    do_something();
    chThdSleepUntil(time);
  }
}
 * @endcode
 * Using this code @p do_something() will always be executed at an absolute
 * deadline time and the error will not accumulate over time regardless of
 * the execution time and delays inserted by other threads.
 */