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diff --git a/docs/src/events.dox b/docs/src/events.dox new file mode 100644 index 000000000..22e4afec7 --- /dev/null +++ b/docs/src/events.dox @@ -0,0 +1,123 @@ +/*
+ 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_events Events Explained
+ * Events are an important feature in ChibiOS/RT, most device drivers generate
+ * events in order to notify the application that something happened at the
+ * I/O level.<br>
+ * While event flags are not something unknown in other operating systems,
+ * their peculiar implementation in ChibiOS/RT requires a more in depth
+ * explanation.<br>
+ * Lets start with the events related terminology:
+ * - <b>Event Source</b>, an @p EventSource is a system object that can be
+ * @a broadcasted asynchronously in response of a system event, as example,
+ * when the CAN driver receives a packet from the CAN bus it @a broadcasts
+ * an event source in order to inform the registered threads that a packet
+ * has just arrived.
+ * - <b>Broadcast</b>, the operation performed on an event source in order
+ * to inform the @a registered threads that an event just occurred.
+ * Broadcasting can happened both in interrupt handlers and in threads.
+ * - <b>Event Listener</b>, a system object that associates a @p Thread object
+ * to an event source. The process of associating a @p Thread to an
+ * @p EventSource using an @p EventListener is called @a registration.
+ * - <b>Registration</b>, action performed by a thread in order to be informed
+ * of events from a specific event source. Of course a thread can be
+ * @a registered on more than one event source by using multiple
+ * @p EventListener objects. Threads can also @a unregister from an event
+ * source.
+ * - <b>Pend</b>, each thread has a mask of @a pending events. The @a broadcast
+ * operation @a pends an event mask on all the @a registered threads.
+ * - <b>Wait</b>, synchronous operation performed by a thread in order to
+ * @a wait a specific combination of events. The API offers a variety of
+ * @a wait functions, please refer to the events API documentation.
+ * .
+ * Note that events are asynchronously generated, as example in an interrupt
+ * handler, but are synchronously served.
+ *
+ * <h2>Events related data structures</h2>
+ * The following diagram explains the relationship between an event source,
+ * its list of event listeners and the @a registered threads.
+ * @dot
+ digraph example {
+ rankdir="LR";
+
+ node [shape=rectangle, fontname=Helvetica, fontsize=8,
+ fixedsize="true", width="1.0", height="0.5"];
+ edge [fontname=Helvetica, fontsize=8, sep=3.0];
+
+ es [shape=record, label="EventSource | es_next", style="bold"];
+
+ subgraph cluster_0 {
+ fontname=Helvetica;
+ label = "Listeners List";
+ color = blue;
+ node [shape=record, fontname=Helvetica, fontsize=8,
+ fixedsize="true", width="1.5", height="1.0"];
+ el4 [label="EventListener 4 | el_mask: 0x0001 | el_listener | el_next"];
+ el3 [label="EventListener 3 | el_mask: 0x0C00 | el_listener | el_next"];
+ el2 [label="EventListener 2 | el_mask: 0x0001 | el_listener | el_next"];
+ el1 [label="EventListener 1 | el_mask: 0x0004 | el_listener | el_next"];
+ el1 -> el2 -> el3 -> el4 [label=" el_next", constraint=false];
+ }
+
+ subgraph cluster_1 {
+ fontname=Helvetica;
+ label = "Registered Threads";
+ color = blue;
+ node [shape=record, fontname=Helvetica, fontsize=8,
+ fixedsize="true", width="1.5", height="0.8"];
+ t1 [label="Thread 1 | p_epending:0x0000 | p_ewmask:0xFFFF"];
+ t2 [label="Thread 2 | p_epending:0x000F | p_ewmask:0x0C01"];
+ t3 [label="Thread 3 | p_epending:0x0008 | p_ewmask:0x0001"];
+ t4 [label="Thread 4 | p_epending:0x0000 | p_ewmask:0xFFFF"];
+ }
+
+ es -> el1 [label=" es_next"];
+ el4 -> es [label=" el_next"];
+ el1 -> t1 [label="el_listener"];
+ el2 -> t2 [label="el_listener"];
+ el3 -> t3 [label="el_listener"];
+ el4 -> t4 [label="el_listener"];
+ }
+ * @enddot
+ * Note that each event listener has a different bit mask to be @a pended on
+ * its associated thread when the event source is @a broadcasted, this means
+ * that each thread can define its own event identifiers independently. A
+ * @a broadcast operation can also @a pend more than one bit on the
+ * @a registered threads.<br>
+ * The threads have a variety of @a wait primitives, they can @a wait for one
+ * or more event flags to become @a pending, and can also specify AND/OR
+ * conditions, as example a thread can @a wait for any event to become
+ * @a pending or @w wait for all the specified events to become @a pending.<br>
+ * The field @p p_epending is the mask of the currently pending events,
+ * the field @p p_ewmask is the mask of the events the thread is interested
+ * on in that moment (AND or OR condition depending on the invoked
+ * @a wait API).
+ *
+ * <h2>Use Scenarios</h2>
+ * Events are best used when one of more of the following conditions are
+ * required:
+ * - Having to wait on multiple conditions, Events are the only mechanism
+ * that easily allow that.
+ * - Synchronous response to one or more asynchronous events.
+ * - Single threaded applications working in a event driver environment (but
+ * events are not limited to single threaded applications).
+ * .
+ */
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