projects / deliverable / linux.git / blame
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|---|---|---|
| dd966083 SA |
1 | <title>Event Interface</title> |
| 2 | ||
| 3 | <para>The V4L2 event interface provides means for user to get | |
| 4 | immediately notified on certain conditions taking place on a device. | |
| 5 | This might include start of frame or loss of signal events, for | |
| 6 | example. | |
| 7 | </para> | |
| 8 | ||
| 9 | <para>To receive events, the events the user is interested in first must | |
| 10 | be subscribed using the &VIDIOC-SUBSCRIBE-EVENT; ioctl. Once an event is | |
| 11 | subscribed, the events of subscribed types are dequeueable using the | |
| 12 | &VIDIOC-DQEVENT; ioctl. Events may be unsubscribed using | |
| 13 | VIDIOC_UNSUBSCRIBE_EVENT ioctl. The special event type V4L2_EVENT_ALL may | |
| 14 | be used to unsubscribe all the events the driver supports.</para> | |
| 15 | ||
| 16 | <para>The event subscriptions and event queues are specific to file | |
| 17 | handles. Subscribing an event on one file handle does not affect | |
| 18 | other file handles. | |
| 19 | </para> | |
| 20 | ||
| 21 | <para>The information on dequeueable events is obtained by using select or | |
| 22 | poll system calls on video devices. The V4L2 events use POLLPRI events on | |
| 23 | poll system call and exceptions on select system call. </para> | |
| 24 | ||
| 25 | <!-- | |
| 26 | Local Variables: | |
| 27 | mode: sgml | |
| 28 | sgml-parent-document: "v4l2.sgml" | |
| 29 | indent-tabs-mode: nil | |
| 30 | End: | |
| 31 | --> |