60 lines
2.2 KiB
Plaintext
60 lines
2.2 KiB
Plaintext
/*
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ChibiOS/RT - Copyright (C) 2006-2007 Giovanni Di Sirio.
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This file is part of ChibiOS/RT.
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ChibiOS/RT is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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ChibiOS/RT is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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/**
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* @page article_timing Reliable timings using Threads
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* One common task is to have threads do something at regular, scheduled,
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* intervals.
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* An obvious solution is to write something like this:
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* @code
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msg_t my_thread(void *param) {
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while (TRUE) {
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do_something();
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chThdSleepMilliseconds(1000); /* Fixed interval */
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}
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}
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* @endcode
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* This example works well assuming that @p do_something() execution time is
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* well below the system tick period and that @p my_thread() is not preempted
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* by other threads inserting long intervals.<br>
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* If the above conditions are not satisfied you may have @p do_something()
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* executed at irregular intervals, as example:<br><br>
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* T0...T0+1000...T0+2002...T0+3002...T0+4005...etc.<br><br>
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* Also note that the error increases over time and this kind of behavior can
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* lead to anomalies really hard to debug.
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* <h2>A better solution</h2>
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* It is possible to rewrite the above code using absolute deadlines rather
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* than fixed intervals:
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* @code
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msg_t my_thread(void *param) {
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systick_t time = chTimeNow(); /* T0 */
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while (TRUE) {
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time += MS2ST(1000); /* Next deadline */
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do_something();
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chThdSleepUntil(time);
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}
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}
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* @endcode
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* Using this code @p do_something() will always be executed at an absolute
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* deadline time and the error will not accumulate over time regardless of
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* the execution time and delays inserted by other threads.
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*/
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