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@@ -1,9 +1,10 @@
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<title>Event Interface</title>
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- <para>The V4L2 event interface provides means for user to get
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+ <para>The V4L2 event interface provides a means for a user to get
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immediately notified on certain conditions taking place on a device.
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This might include start of frame or loss of signal events, for
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- example.
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+ example. Changes in the value or state of a V4L2 control can also be
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+ reported through events.
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</para>
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<para>To receive events, the events the user is interested in first must
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@@ -15,12 +16,31 @@
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<para>The event subscriptions and event queues are specific to file
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handles. Subscribing an event on one file handle does not affect
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- other file handles.
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- </para>
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+ other file handles.</para>
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<para>The information on dequeueable events is obtained by using select or
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poll system calls on video devices. The V4L2 events use POLLPRI events on
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- poll system call and exceptions on select system call. </para>
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+ poll system call and exceptions on select system call.</para>
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+
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+ <para>Starting with kernel 3.1 certain guarantees can be given with
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+ regards to events:<orderedlist>
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+ <listitem>
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+ <para>Each subscribed event has its own internal dedicated event queue.
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+This means that flooding of one event type will not interfere with other
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+event types.</para>
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+ </listitem>
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+ <listitem>
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+ <para>If the internal event queue for a particular subscribed event
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+becomes full, then the oldest event in that queue will be dropped.</para>
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+ </listitem>
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+ <listitem>
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+ <para>Where applicable, certain event types can ensure that the payload
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+of the oldest event that is about to be dropped will be merged with the payload
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+of the next oldest event. Thus ensuring that no information is lost, but only an
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+intermediate step leading up to that information. See the documentation for the
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+event you want to subscribe to whether this is applicable for that event or not.</para>
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+ </listitem>
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+ </orderedlist></para>
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<!--
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Local Variables:
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