mirror of
https://mirrors.bfsu.edu.cn/git/linux.git
synced 2024-12-15 06:55:13 +08:00
eab00a0da2
Define a frame sync event to tell user space when the reception of a frame starts. Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi> Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
207 lines
7.0 KiB
XML
207 lines
7.0 KiB
XML
<refentry id="vidioc-subscribe-event">
|
|
<refmeta>
|
|
<refentrytitle>ioctl VIDIOC_SUBSCRIBE_EVENT, VIDIOC_UNSUBSCRIBE_EVENT</refentrytitle>
|
|
&manvol;
|
|
</refmeta>
|
|
|
|
<refnamediv>
|
|
<refname>VIDIOC_SUBSCRIBE_EVENT, VIDIOC_UNSUBSCRIBE_EVENT</refname>
|
|
<refpurpose>Subscribe or unsubscribe event</refpurpose>
|
|
</refnamediv>
|
|
|
|
<refsynopsisdiv>
|
|
<funcsynopsis>
|
|
<funcprototype>
|
|
<funcdef>int <function>ioctl</function></funcdef>
|
|
<paramdef>int <parameter>fd</parameter></paramdef>
|
|
<paramdef>int <parameter>request</parameter></paramdef>
|
|
<paramdef>struct v4l2_event_subscription
|
|
*<parameter>argp</parameter></paramdef>
|
|
</funcprototype>
|
|
</funcsynopsis>
|
|
</refsynopsisdiv>
|
|
|
|
<refsect1>
|
|
<title>Arguments</title>
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term><parameter>fd</parameter></term>
|
|
<listitem>
|
|
<para>&fd;</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><parameter>request</parameter></term>
|
|
<listitem>
|
|
<para>VIDIOC_SUBSCRIBE_EVENT, VIDIOC_UNSUBSCRIBE_EVENT</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><parameter>argp</parameter></term>
|
|
<listitem>
|
|
<para></para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>Description</title>
|
|
|
|
<para>Subscribe or unsubscribe V4L2 event. Subscribed events are
|
|
dequeued by using the &VIDIOC-DQEVENT; ioctl.</para>
|
|
|
|
<table frame="none" pgwide="1" id="v4l2-event-subscription">
|
|
<title>struct <structname>v4l2_event_subscription</structname></title>
|
|
<tgroup cols="3">
|
|
&cs-str;
|
|
<tbody valign="top">
|
|
<row>
|
|
<entry>__u32</entry>
|
|
<entry><structfield>type</structfield></entry>
|
|
<entry>Type of the event.</entry>
|
|
</row>
|
|
<row>
|
|
<entry>__u32</entry>
|
|
<entry><structfield>id</structfield></entry>
|
|
<entry>ID of the event source. If there is no ID associated with
|
|
the event source, then set this to 0. Whether or not an event
|
|
needs an ID depends on the event type.</entry>
|
|
</row>
|
|
<row>
|
|
<entry>__u32</entry>
|
|
<entry><structfield>flags</structfield></entry>
|
|
<entry>Event flags, see <xref linkend="event-flags" />.</entry>
|
|
</row>
|
|
<row>
|
|
<entry>__u32</entry>
|
|
<entry><structfield>reserved</structfield>[5]</entry>
|
|
<entry>Reserved for future extensions. Drivers and applications
|
|
must set the array to zero.</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
|
|
<table frame="none" pgwide="1" id="event-type">
|
|
<title>Event Types</title>
|
|
<tgroup cols="3">
|
|
&cs-def;
|
|
<tbody valign="top">
|
|
<row>
|
|
<entry><constant>V4L2_EVENT_ALL</constant></entry>
|
|
<entry>0</entry>
|
|
<entry>All events. V4L2_EVENT_ALL is valid only for
|
|
VIDIOC_UNSUBSCRIBE_EVENT for unsubscribing all events at once.
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_EVENT_VSYNC</constant></entry>
|
|
<entry>1</entry>
|
|
<entry>This event is triggered on the vertical sync.
|
|
This event has a &v4l2-event-vsync; associated with it.
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_EVENT_EOS</constant></entry>
|
|
<entry>2</entry>
|
|
<entry>This event is triggered when the end of a stream is reached.
|
|
This is typically used with MPEG decoders to report to the application
|
|
when the last of the MPEG stream has been decoded.
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_EVENT_CTRL</constant></entry>
|
|
<entry>3</entry>
|
|
<entry><para>This event requires that the <structfield>id</structfield>
|
|
matches the control ID from which you want to receive events.
|
|
This event is triggered if the control's value changes, if a
|
|
button control is pressed or if the control's flags change.
|
|
This event has a &v4l2-event-ctrl; associated with it. This struct
|
|
contains much of the same information as &v4l2-queryctrl; and
|
|
&v4l2-control;.</para>
|
|
|
|
<para>If the event is generated due to a call to &VIDIOC-S-CTRL; or
|
|
&VIDIOC-S-EXT-CTRLS;, then the event will <emphasis>not</emphasis> be sent to
|
|
the file handle that called the ioctl function. This prevents
|
|
nasty feedback loops. If you <emphasis>do</emphasis> want to get the
|
|
event, then set the <constant>V4L2_EVENT_SUB_FL_ALLOW_FEEDBACK</constant>
|
|
flag.
|
|
</para>
|
|
|
|
<para>This event type will ensure that no information is lost when
|
|
more events are raised than there is room internally. In that
|
|
case the &v4l2-event-ctrl; of the second-oldest event is kept,
|
|
but the <structfield>changes</structfield> field of the
|
|
second-oldest event is ORed with the <structfield>changes</structfield>
|
|
field of the oldest event.</para>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_EVENT_FRAME_SYNC</constant></entry>
|
|
<entry>4</entry>
|
|
<entry>
|
|
<para>Triggered immediately when the reception of a
|
|
frame has begun. This event has a
|
|
&v4l2-event-frame-sync; associated with it.</para>
|
|
|
|
<para>If the hardware needs to be stopped in the case of a
|
|
buffer underrun it might not be able to generate this event.
|
|
In such cases the <structfield>frame_sequence</structfield>
|
|
field in &v4l2-event-frame-sync; will not be incremented. This
|
|
causes two consecutive frame sequence numbers to have n times
|
|
frame interval in between them.</para>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_EVENT_PRIVATE_START</constant></entry>
|
|
<entry>0x08000000</entry>
|
|
<entry>Base event number for driver-private events.</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
|
|
<table pgwide="1" frame="none" id="event-flags">
|
|
<title>Event Flags</title>
|
|
<tgroup cols="3">
|
|
&cs-def;
|
|
<tbody valign="top">
|
|
<row>
|
|
<entry><constant>V4L2_EVENT_SUB_FL_SEND_INITIAL</constant></entry>
|
|
<entry>0x0001</entry>
|
|
<entry>When this event is subscribed an initial event will be sent
|
|
containing the current status. This only makes sense for events
|
|
that are triggered by a status change such as <constant>V4L2_EVENT_CTRL</constant>.
|
|
Other events will ignore this flag.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_EVENT_SUB_FL_ALLOW_FEEDBACK</constant></entry>
|
|
<entry>0x0002</entry>
|
|
<entry><para>If set, then events directly caused by an ioctl will also be sent to
|
|
the filehandle that called that ioctl. For example, changing a control using
|
|
&VIDIOC-S-CTRL; will cause a V4L2_EVENT_CTRL to be sent back to that same
|
|
filehandle. Normally such events are suppressed to prevent feedback loops
|
|
where an application changes a control to a one value and then another, and
|
|
then receives an event telling it that that control has changed to the first
|
|
value.</para>
|
|
|
|
<para>Since it can't tell whether that event was caused by another application
|
|
or by the &VIDIOC-S-CTRL; call it is hard to decide whether to set the
|
|
control to the value in the event, or ignore it.</para>
|
|
|
|
<para>Think carefully when you set this flag so you won't get into situations
|
|
like that.</para>
|
|
</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
|
|
</refsect1>
|
|
<refsect1>
|
|
&return-value;
|
|
</refsect1>
|
|
</refentry>
|