32 lines
1.1 KiB
XML
32 lines
1.1 KiB
XML
|
<title>Event Interface</title>
|
||
|
|
|
||
|
|
<para>The V4L2 event interface provides means for user to get
|
||
|
|
immediately notified on certain conditions taking place on a device.
|
||
|
|
This might include start of frame or loss of signal events, for
|
||
|
|
example.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>To receive events, the events the user is interested in first must
|
||
|
|
be subscribed using the &VIDIOC-SUBSCRIBE-EVENT; ioctl. Once an event is
|
||
|
|
subscribed, the events of subscribed types are dequeueable using the
|
||
|
|
&VIDIOC-DQEVENT; ioctl. Events may be unsubscribed using
|
||
|
|
VIDIOC_UNSUBSCRIBE_EVENT ioctl. The special event type V4L2_EVENT_ALL may
|
||
|
|
be used to unsubscribe all the events the driver supports.</para>
|
||
|
|
|
||
|
|
<para>The event subscriptions and event queues are specific to file
|
||
|
|
handles. Subscribing an event on one file handle does not affect
|
||
|
|
other file handles.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>The information on dequeueable events is obtained by using select or
|
||
|
|
poll system calls on video devices. The V4L2 events use POLLPRI events on
|
||
|
|
poll system call and exceptions on select system call. </para>
|
||
|
|
|
||
|
|
<!--
|
||
|
|
Local Variables:
|
||
|
|
mode: sgml
|
||
|
|
sgml-parent-document: "v4l2.sgml"
|
||
|
|
indent-tabs-mode: nil
|
||
|
|
End:
|
||
|
|
-->
|