--- /dev/null
+<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.</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>
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