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-<refentry id="vidioc-dqevent">
- <refmeta>
- <refentrytitle>ioctl VIDIOC_DQEVENT</refentrytitle>
- &manvol;
- </refmeta>
-
- <refnamediv>
- <refname>VIDIOC_DQEVENT</refname>
- <refpurpose>Dequeue 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
-*<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_DQEVENT</para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><parameter>argp</parameter></term>
- <listitem>
- <para></para>
- </listitem>
- </varlistentry>
- </variablelist>
- </refsect1>
-
- <refsect1>
- <title>Description</title>
-
- <para>Dequeue an event from a video device. No input is required
- for this ioctl. All the fields of the &v4l2-event; structure are
- filled by the driver. The file handle will also receive exceptions
- which the application may get by e.g. using the select system
- call.</para>
-
- <table frame="none" pgwide="1" id="v4l2-event">
- <title>struct <structname>v4l2_event</structname></title>
- <tgroup cols="4">
- &cs-str;
- <tbody valign="top">
- <row>
- <entry>__u32</entry>
- <entry><structfield>type</structfield></entry>
- <entry></entry>
- <entry>Type of the event, see <xref linkend="event-type" />.</entry>
- </row>
- <row>
- <entry>union</entry>
- <entry><structfield>u</structfield></entry>
- <entry></entry>
- <entry></entry>
- </row>
- <row>
- <entry></entry>
- <entry>&v4l2-event-vsync;</entry>
- <entry><structfield>vsync</structfield></entry>
- <entry>Event data for event <constant>V4L2_EVENT_VSYNC</constant>.
- </entry>
- </row>
- <row>
- <entry></entry>
- <entry>&v4l2-event-ctrl;</entry>
- <entry><structfield>ctrl</structfield></entry>
- <entry>Event data for event <constant>V4L2_EVENT_CTRL</constant>.
- </entry>
- </row>
- <row>
- <entry></entry>
- <entry>&v4l2-event-frame-sync;</entry>
- <entry><structfield>frame_sync</structfield></entry>
- <entry>Event data for event
- <constant>V4L2_EVENT_FRAME_SYNC</constant>.</entry>
- </row>
- <row>
- <entry></entry>
- <entry>&v4l2-event-motion-det;</entry>
- <entry><structfield>motion_det</structfield></entry>
- <entry>Event data for event V4L2_EVENT_MOTION_DET.</entry>
- </row>
- <row>
- <entry></entry>
- <entry>&v4l2-event-src-change;</entry>
- <entry><structfield>src_change</structfield></entry>
- <entry>Event data for event V4L2_EVENT_SOURCE_CHANGE.</entry>
- </row>
- <row>
- <entry></entry>
- <entry>__u8</entry>
- <entry><structfield>data</structfield>[64]</entry>
- <entry>Event data. Defined by the event type. The union
- should be used to define easily accessible type for
- events.</entry>
- </row>
- <row>
- <entry>__u32</entry>
- <entry><structfield>pending</structfield></entry>
- <entry></entry>
- <entry>Number of pending events excluding this one.</entry>
- </row>
- <row>
- <entry>__u32</entry>
- <entry><structfield>sequence</structfield></entry>
- <entry></entry>
- <entry>Event sequence number. The sequence number is
- incremented for every subscribed event that takes place.
- If sequence numbers are not contiguous it means that
- events have been lost.
- </entry>
- </row>
- <row>
- <entry>struct timespec</entry>
- <entry><structfield>timestamp</structfield></entry>
- <entry></entry>
- <entry>Event timestamp. The timestamp has been taken from the
- <constant>CLOCK_MONOTONIC</constant> clock. To access the
- same clock outside V4L2, use <function>clock_gettime(2)</function>.
- </entry>
- </row>
- <row>
- <entry>u32</entry>
- <entry><structfield>id</structfield></entry>
- <entry></entry>
- <entry>The ID associated with the event source. If the event does not
- have an associated ID (this depends on the event type), then this
- is 0.</entry>
- </row>
- <row>
- <entry>__u32</entry>
- <entry><structfield>reserved</structfield>[8]</entry>
- <entry></entry>
- <entry>Reserved for future extensions. Drivers 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_SOURCE_CHANGE</constant></entry>
- <entry>5</entry>
- <entry>
- <para>This event is triggered when a source parameter change is
- detected during runtime by the video device. It can be a
- runtime resolution change triggered by a video decoder or the
- format change happening on an input connector.
- This event requires that the <structfield>id</structfield>
- matches the input index (when used with a video device node)
- or the pad index (when used with a subdevice node) from which
- you want to receive events.</para>
-
- <para>This event has a &v4l2-event-src-change; associated
- with it. The <structfield>changes</structfield> bitfield denotes
- what has changed for the subscribed pad. If multiple events
- occurred before application could dequeue them, then the changes
- will have the ORed value of all the events generated.</para>
- </entry>
- </row>
- <row>
- <entry><constant>V4L2_EVENT_MOTION_DET</constant></entry>
- <entry>6</entry>
- <entry>
- <para>Triggered whenever the motion detection state for one or more of the regions
- changes. This event has a &v4l2-event-motion-det; associated with it.</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 frame="none" pgwide="1" id="v4l2-event-vsync">
- <title>struct <structname>v4l2_event_vsync</structname></title>
- <tgroup cols="3">
- &cs-str;
- <tbody valign="top">
- <row>
- <entry>__u8</entry>
- <entry><structfield>field</structfield></entry>
- <entry>The upcoming field. See &v4l2-field;.</entry>
- </row>
- </tbody>
- </tgroup>
- </table>
-
- <table frame="none" pgwide="1" id="v4l2-event-ctrl">
- <title>struct <structname>v4l2_event_ctrl</structname></title>
- <tgroup cols="4">
- &cs-str;
- <tbody valign="top">
- <row>
- <entry>__u32</entry>
- <entry><structfield>changes</structfield></entry>
- <entry></entry>
- <entry>A bitmask that tells what has changed. See <xref linkend="ctrl-changes-flags" />.</entry>
- </row>
- <row>
- <entry>__u32</entry>
- <entry><structfield>type</structfield></entry>
- <entry></entry>
- <entry>The type of the control. See &v4l2-ctrl-type;.</entry>
- </row>
- <row>
- <entry>union (anonymous)</entry>
- <entry></entry>
- <entry></entry>
- <entry></entry>
- </row>
- <row>
- <entry></entry>
- <entry>__s32</entry>
- <entry><structfield>value</structfield></entry>
- <entry>The 32-bit value of the control for 32-bit control types.
- This is 0 for string controls since the value of a string
- cannot be passed using &VIDIOC-DQEVENT;.</entry>
- </row>
- <row>
- <entry></entry>
- <entry>__s64</entry>
- <entry><structfield>value64</structfield></entry>
- <entry>The 64-bit value of the control for 64-bit control types.</entry>
- </row>
- <row>
- <entry>__u32</entry>
- <entry><structfield>flags</structfield></entry>
- <entry></entry>
- <entry>The control flags. See <xref linkend="control-flags" />.</entry>
- </row>
- <row>
- <entry>__s32</entry>
- <entry><structfield>minimum</structfield></entry>
- <entry></entry>
- <entry>The minimum value of the control. See &v4l2-queryctrl;.</entry>
- </row>
- <row>
- <entry>__s32</entry>
- <entry><structfield>maximum</structfield></entry>
- <entry></entry>
- <entry>The maximum value of the control. See &v4l2-queryctrl;.</entry>
- </row>
- <row>
- <entry>__s32</entry>
- <entry><structfield>step</structfield></entry>
- <entry></entry>
- <entry>The step value of the control. See &v4l2-queryctrl;.</entry>
- </row>
- <row>
- <entry>__s32</entry>
- <entry><structfield>default_value</structfield></entry>
- <entry></entry>
- <entry>The default value value of the control. See &v4l2-queryctrl;.</entry>
- </row>
- </tbody>
- </tgroup>
- </table>
-
- <table frame="none" pgwide="1" id="v4l2-event-frame-sync">
- <title>struct <structname>v4l2_event_frame_sync</structname></title>
- <tgroup cols="3">
- &cs-str;
- <tbody valign="top">
- <row>
- <entry>__u32</entry>
- <entry><structfield>frame_sequence</structfield></entry>
- <entry>
- The sequence number of the frame being received.
- </entry>
- </row>
- </tbody>
- </tgroup>
- </table>
-
- <table frame="none" pgwide="1" id="v4l2-event-src-change">
- <title>struct <structname>v4l2_event_src_change</structname></title>
- <tgroup cols="3">
- &cs-str;
- <tbody valign="top">
- <row>
- <entry>__u32</entry>
- <entry><structfield>changes</structfield></entry>
- <entry>
- A bitmask that tells what has changed. See <xref linkend="src-changes-flags" />.
- </entry>
- </row>
- </tbody>
- </tgroup>
- </table>
-
- <table frame="none" pgwide="1" id="v4l2-event-motion-det">
- <title>struct <structname>v4l2_event_motion_det</structname></title>
- <tgroup cols="3">
- &cs-str;
- <tbody valign="top">
- <row>
- <entry>__u32</entry>
- <entry><structfield>flags</structfield></entry>
- <entry>
- Currently only one flag is available: if <constant>V4L2_EVENT_MD_FL_HAVE_FRAME_SEQ</constant>
- is set, then the <structfield>frame_sequence</structfield> field is valid,
- otherwise that field should be ignored.
- </entry>
- </row>
- <row>
- <entry>__u32</entry>
- <entry><structfield>frame_sequence</structfield></entry>
- <entry>
- The sequence number of the frame being received. Only valid if the
- <constant>V4L2_EVENT_MD_FL_HAVE_FRAME_SEQ</constant> flag was set.
- </entry>
- </row>
- <row>
- <entry>__u32</entry>
- <entry><structfield>region_mask</structfield></entry>
- <entry>
- The bitmask of the regions that reported motion. There is at least one
- region. If this field is 0, then no motion was detected at all.
- If there is no <constant>V4L2_CID_DETECT_MD_REGION_GRID</constant> control
- (see <xref linkend="detect-controls" />) to assign a different region
- to each cell in the motion detection grid, then that all cells
- are automatically assigned to the default region 0.
- </entry>
- </row>
- </tbody>
- </tgroup>
- </table>
-
- <table pgwide="1" frame="none" id="ctrl-changes-flags">
- <title>Control Changes</title>
- <tgroup cols="3">
- &cs-def;
- <tbody valign="top">
- <row>
- <entry><constant>V4L2_EVENT_CTRL_CH_VALUE</constant></entry>
- <entry>0x0001</entry>
- <entry>This control event was triggered because the value of the control
- changed. Special cases: Volatile controls do no generate this event;
- If a control has the <constant>V4L2_CTRL_FLAG_EXECUTE_ON_WRITE</constant>
- flag set, then this event is sent as well, regardless its value.</entry>
- </row>
- <row>
- <entry><constant>V4L2_EVENT_CTRL_CH_FLAGS</constant></entry>
- <entry>0x0002</entry>
- <entry>This control event was triggered because the control flags
- changed.</entry>
- </row>
- <row>
- <entry><constant>V4L2_EVENT_CTRL_CH_RANGE</constant></entry>
- <entry>0x0004</entry>
- <entry>This control event was triggered because the minimum,
- maximum, step or the default value of the control changed.</entry>
- </row>
- </tbody>
- </tgroup>
- </table>
-
- <table pgwide="1" frame="none" id="src-changes-flags">
- <title>Source Changes</title>
- <tgroup cols="3">
- &cs-def;
- <tbody valign="top">
- <row>
- <entry><constant>V4L2_EVENT_SRC_CH_RESOLUTION</constant></entry>
- <entry>0x0001</entry>
- <entry>This event gets triggered when a resolution change is
- detected at an input. This can come from an input connector or
- from a video decoder.
- </entry>
- </row>
- </tbody>
- </tgroup>
- </table>
- </refsect1>
- <refsect1>
- &return-value;
- </refsect1>
-</refentry>