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| <h1 id="event-queues">Event Queues</h1> |
| <p>Event queue is a way of serializing events arring to a task. This makes it easy to queue processing to happen inside task's context. This would be done either from an interrupt handler, or from another task.</p> |
| <p>Events arrive in a form of a data structure <em>struct os_event</em>.</p> |
| <h3 id="description">Description</h3> |
| <p>Events are in form of a data structure <em>struct os_event</em>, and they are queued to data structure <em>struct os_eventq</em>.</p> |
| <p>Queue must be initialized before trying to add events to it. This is done using <em>os_eventq_init()</em>.</p> |
| <p>Common way of using event queues is to have a task loop while calling <em>os_eventq_get()</em>, waiting for work to do. |
| Other tasks (or interrupts) then call <em>os_eventq_put()</em> to wake it up. Once event has been queued task waiting on that queue is woken up, and will get a pointer to queued event structure. |
| Processing task would then act according to event type.</p> |
| <p>When <em>os_event</em> is queued, it should not be freed until processing task is done with it.</p> |
| <p>It is assumed that there is only one task consuming events from an event queue. Only one task should be sleeping on a particular <em>os_eventq</em> at a time.</p> |
| <p>Note that os_callout subsystem assumes that event queue is used as the wakeup mechanism.</p> |
| <h3 id="data-structures">Data structures</h3> |
| <div class="codehilite" style="background: #ffffff"><pre style="line-height: 125%;"><span></span><code><span style="color: #A90D91">struct</span> <span style="color: #3F6E75">os_event</span> { |
| <span style="color: #A90D91">uint8_t</span> <span style="color: #000000">ev_queued</span>; |
| <span style="color: #A90D91">uint8_t</span> <span style="color: #000000">ev_type</span>; |
| <span style="color: #A90D91">void</span> <span style="color: #000000">*ev_arg</span>; |
| <span style="color: #000000">STAILQ_ENTRY</span>(<span style="color: #000000">os_event</span>) <span style="color: #000000">ev_next</span>; |
| }; |
| </code></pre></div> |
| |
| <table> |
| <thead> |
| <tr> |
| <th>Element</th> |
| <th>Description</th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr> |
| <td>ev_queued</td> |
| <td>Internal field, which tells whether event is linked into an <em>os_eventq</em> already</td> |
| </tr> |
| <tr> |
| <td>ev_type</td> |
| <td>Type of an event. This should be unique, as it should be used by processing task to figure out what the event means</td> |
| </tr> |
| <tr> |
| <td>ev_arg</td> |
| <td>Can be used further as input to task processing this event</td> |
| </tr> |
| <tr> |
| <td>ev_next</td> |
| <td>Linkage attaching this event to an event queue</td> |
| </tr> |
| </tbody> |
| </table> |
| <div class="codehilite" style="background: #ffffff"><pre style="line-height: 125%;"><span></span><code><span style="color: #A90D91">struct</span> <span style="color: #3F6E75">os_eventq</span> { |
| <span style="color: #A90D91">struct</span> <span style="color: #3F6E75">os_task</span> <span style="color: #000000">*evq_task</span>; |
| <span style="color: #000000">STAILQ_HEAD</span>(, <span style="color: #000000">os_event</span>) <span style="color: #000000">evq_list</span>; |
| }; |
| </code></pre></div> |
| |
| <table> |
| <thead> |
| <tr> |
| <th>Element</th> |
| <th>Description</th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr> |
| <td>evq_task</td> |
| <td>Pointer to task if there is task sleeping on <em>os_eventq_get()</em></td> |
| </tr> |
| <tr> |
| <td>evq_list</td> |
| <td>Queue head for list of events in this queue</td> |
| </tr> |
| </tbody> |
| </table> |
| <h3 id="list-of-functions">List of Functions</h3> |
| <p>The functions available in event queue feature are:</p> |
| <table> |
| <thead> |
| <tr> |
| <th><strong>Function</strong></th> |
| <th><strong>Description</strong></th> |
| </tr> |
| </thead> |
| <tbody> |
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| <td><a href="../os_eventq_get/">os_eventq_get</a></td> |
| <td>Fetches the first event from a queue. Task will sleep until something gets queued.</td> |
| </tr> |
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| <td><a href="../os_eventq_init/">os_eventq_init</a></td> |
| <td>Initializes the given event queue, making it ready for use.</td> |
| </tr> |
| <tr> |
| <td><a href="../os_eventq_put/">os_eventq_put</a></td> |
| <td>Queues an event to tail of the event queue.</td> |
| </tr> |
| <tr> |
| <td><a href="../os_eventq_remove/">os_eventq_remove</a></td> |
| <td>Removes an event which has been placed in a queue.</td> |
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