import ChibiOS 2.0.8

ChibiOS_2.0.8/docs/src/roundrobin.dox

@@ -0,0 +1,57 @@
+/*
+    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/>.
+
+                                      ---
+
+    A special exception to the GPL can be applied should you wish to distribute
+    a combined work that includes ChibiOS/RT, without being obliged to provide
+    the source code for any proprietary components. See the file exception.txt
+    for full details of how and when the exception can be applied.
+*/
+
+/**
+ * @page article_roundrobin Round Robin scheduling explained
+ * Unlike many other RTOSes, ChibiOS/RT supports multiple threads at the
+ * same priority level and schedules them using an <i>aggressive</i>
+ * round-robin strategy.<br>
+ * The strategy is defined as aggressive because any scheduling event
+ * causes the round-robin threads to rotate.<br>
+ * A round-robin rotation can happen because of the following events:
+ * - The currently executed thread voluntarily invokes the @p chThdYield()
+ *   API in order to allow the execution of another thread at the same
+ *   priority level, if any.
+ * - The currently executed thread voluntarily goes into a sleep state
+ *   (see @ref thread_states), when the thread is awakened it goes behind
+ *   any other thread at the same priority level.
+ * - The currently executed thread is preempted by an higher priority
+ *   thread, the thread is reinserted in the ready list (see @ref scheduling)
+ *   behind any other thread at the same priority level.
+ * - If the @p CH_TIME_QUANTUM configuration constant is set to a value
+ *   greater than zero and if the specified time quantum expired and if
+ *   a thread with equal priority is ready then the currently executing
+ *   thread is automatically reinserted in the ready list behind any
+ *   other thread at the same priority level.
+ * .
+ * As you can see the @p CH_TIME_QUANTUM setting is really useful only if
+ * there are threads at the same priority level that can run not preempted
+ * for long periods of time and that do not explicitly yield using
+ * @p chThdYield(). Because of this you should consider setting
+ * @p CH_TIME_QUANTUM to zero in your configuration file, this makes the
+ * kernel much faster and smaller and <b>does not</b> forbid the use of
+ * multiple threads at the same priority level.
+ */