| <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> |
