mirror of https://gitee.com/openkylin/linux.git
32 lines
1.1 KiB
XML
32 lines
1.1 KiB
XML
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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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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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</para>
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<para>To receive events, the events the user is interested in first must
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be subscribed using the &VIDIOC-SUBSCRIBE-EVENT; ioctl. Once an event is
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subscribed, the events of subscribed types are dequeueable using the
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&VIDIOC-DQEVENT; ioctl. Events may be unsubscribed using
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VIDIOC_UNSUBSCRIBE_EVENT ioctl. The special event type V4L2_EVENT_ALL may
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be used to unsubscribe all the events the driver supports.</para>
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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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<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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<!--
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Local Variables:
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mode: sgml
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sgml-parent-document: "v4l2.sgml"
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indent-tabs-mode: nil
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End:
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-->
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