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Based on kernel version 4.1. Page generated on 2015-06-28 12:12 EST.

1	<refentry id="vidioc-dqevent">
2	  <refmeta>
3	    <refentrytitle>ioctl VIDIOC_DQEVENT</refentrytitle>
4	    &manvol;
5	  </refmeta>
6	
7	  <refnamediv>
8	    <refname>VIDIOC_DQEVENT</refname>
9	    <refpurpose>Dequeue event</refpurpose>
10	  </refnamediv>
11	
12	  <refsynopsisdiv>
13	    <funcsynopsis>
14	      <funcprototype>
15		<funcdef>int <function>ioctl</function></funcdef>
16		<paramdef>int <parameter>fd</parameter></paramdef>
17		<paramdef>int <parameter>request</parameter></paramdef>
18		<paramdef>struct v4l2_event
19	*<parameter>argp</parameter></paramdef>
20	      </funcprototype>
21	    </funcsynopsis>
22	  </refsynopsisdiv>
23	
24	  <refsect1>
25	    <title>Arguments</title>
26	
27	    <variablelist>
28	      <varlistentry>
29		<term><parameter>fd</parameter></term>
30		<listitem>
31		  <para>&fd;</para>
32		</listitem>
33	      </varlistentry>
34	      <varlistentry>
35		<term><parameter>request</parameter></term>
36		<listitem>
37		  <para>VIDIOC_DQEVENT</para>
38		</listitem>
39	      </varlistentry>
40	      <varlistentry>
41		<term><parameter>argp</parameter></term>
42		<listitem>
43		  <para></para>
44		</listitem>
45	      </varlistentry>
46	    </variablelist>
47	  </refsect1>
48	
49	  <refsect1>
50	    <title>Description</title>
51	
52	    <para>Dequeue an event from a video device. No input is required
53	    for this ioctl. All the fields of the &v4l2-event; structure are
54	    filled by the driver. The file handle will also receive exceptions
55	    which the application may get by e.g. using the select system
56	    call.</para>
57	
58	    <table frame="none" pgwide="1" id="v4l2-event">
59	      <title>struct <structname>v4l2_event</structname></title>
60	      <tgroup cols="4">
61		&cs-str;
62		<tbody valign="top">
63		  <row>
64		    <entry>__u32</entry>
65		    <entry><structfield>type</structfield></entry>
66	            <entry></entry>
67		    <entry>Type of the event, see <xref linkend="event-type" />.</entry>
68		  </row>
69		  <row>
70		    <entry>union</entry>
71		    <entry><structfield>u</structfield></entry>
72	            <entry></entry>
73		    <entry></entry>
74		  </row>
75		  <row>
76		    <entry></entry>
77		    <entry>&v4l2-event-vsync;</entry>
78	            <entry><structfield>vsync</structfield></entry>
79		    <entry>Event data for event <constant>V4L2_EVENT_VSYNC</constant>.
80	            </entry>
81		  </row>
82		  <row>
83		    <entry></entry>
84		    <entry>&v4l2-event-ctrl;</entry>
85	            <entry><structfield>ctrl</structfield></entry>
86		    <entry>Event data for event <constant>V4L2_EVENT_CTRL</constant>.
87	            </entry>
88		  </row>
89		  <row>
90		    <entry></entry>
91		    <entry>&v4l2-event-frame-sync;</entry>
92	            <entry><structfield>frame_sync</structfield></entry>
93		    <entry>Event data for event
94		    <constant>V4L2_EVENT_FRAME_SYNC</constant>.</entry>
95		  </row>
96		  <row>
97		    <entry></entry>
98		    <entry>&v4l2-event-motion-det;</entry>
99	            <entry><structfield>motion_det</structfield></entry>
100		    <entry>Event data for event V4L2_EVENT_MOTION_DET.</entry>
101		  </row>
102		  <row>
103		    <entry></entry>
104		    <entry>&v4l2-event-src-change;</entry>
105	            <entry><structfield>src_change</structfield></entry>
106		    <entry>Event data for event V4L2_EVENT_SOURCE_CHANGE.</entry>
107		  </row>
108		  <row>
109		    <entry></entry>
110		    <entry>__u8</entry>
111	            <entry><structfield>data</structfield>[64]</entry>
112		    <entry>Event data. Defined by the event type. The union
113	            should be used to define easily accessible type for
114	            events.</entry>
115		  </row>
116		  <row>
117		    <entry>__u32</entry>
118		    <entry><structfield>pending</structfield></entry>
119	            <entry></entry>
120		    <entry>Number of pending events excluding this one.</entry>
121		  </row>
122		  <row>
123		    <entry>__u32</entry>
124		    <entry><structfield>sequence</structfield></entry>
125	            <entry></entry>
126		    <entry>Event sequence number. The sequence number is
127		    incremented for every subscribed event that takes place.
128		    If sequence numbers are not contiguous it means that
129		    events have been lost.
130		    </entry>
131		  </row>
132		  <row>
133		    <entry>struct timespec</entry>
134		    <entry><structfield>timestamp</structfield></entry>
135	            <entry></entry>
136		    <entry>Event timestamp.</entry>
137		  </row>
138		  <row>
139		    <entry>u32</entry>
140		    <entry><structfield>id</structfield></entry>
141	            <entry></entry>
142		    <entry>The ID associated with the event source. If the event does not
143			have an associated ID (this depends on the event type), then this
144			is 0.</entry>
145		  </row>
146		  <row>
147		    <entry>__u32</entry>
148		    <entry><structfield>reserved</structfield>[8]</entry>
149	            <entry></entry>
150		    <entry>Reserved for future extensions. Drivers must set
151		    the array to zero.</entry>
152		  </row>
153		</tbody>
154	      </tgroup>
155	    </table>
156	
157	    <table frame="none" pgwide="1" id="event-type">
158	      <title>Event Types</title>
159	      <tgroup cols="3">
160		&cs-def;
161		<tbody valign="top">
162		  <row>
163		    <entry><constant>V4L2_EVENT_ALL</constant></entry>
164		    <entry>0</entry>
165		    <entry>All events. V4L2_EVENT_ALL is valid only for
166		    VIDIOC_UNSUBSCRIBE_EVENT for unsubscribing all events at once.
167		    </entry>
168		  </row>
169		  <row>
170		    <entry><constant>V4L2_EVENT_VSYNC</constant></entry>
171		    <entry>1</entry>
172		    <entry>This event is triggered on the vertical sync.
173		    This event has a &v4l2-event-vsync; associated with it.
174		    </entry>
175		  </row>
176		  <row>
177		    <entry><constant>V4L2_EVENT_EOS</constant></entry>
178		    <entry>2</entry>
179		    <entry>This event is triggered when the end of a stream is reached.
180		    This is typically used with MPEG decoders to report to the application
181		    when the last of the MPEG stream has been decoded.
182		    </entry>
183		  </row>
184		  <row>
185		    <entry><constant>V4L2_EVENT_CTRL</constant></entry>
186		    <entry>3</entry>
187		    <entry><para>This event requires that the <structfield>id</structfield>
188			matches the control ID from which you want to receive events.
189			This event is triggered if the control's value changes, if a
190			button control is pressed or if the control's flags change.
191		    	This event has a &v4l2-event-ctrl; associated with it. This struct
192			contains much of the same information as &v4l2-queryctrl; and
193			&v4l2-control;.</para>
194	
195			<para>If the event is generated due to a call to &VIDIOC-S-CTRL; or
196			&VIDIOC-S-EXT-CTRLS;, then the event will <emphasis>not</emphasis> be sent to
197			the file handle that called the ioctl function. This prevents
198			nasty feedback loops. If you <emphasis>do</emphasis> want to get the
199			event, then set the <constant>V4L2_EVENT_SUB_FL_ALLOW_FEEDBACK</constant>
200			flag.
201			</para>
202	
203			<para>This event type will ensure that no information is lost when
204			more events are raised than there is room internally. In that
205			case the &v4l2-event-ctrl; of the second-oldest event is kept,
206			but the <structfield>changes</structfield> field of the
207			second-oldest event is ORed with the <structfield>changes</structfield>
208			field of the oldest event.</para>
209		    </entry>
210		  </row>
211		  <row>
212		    <entry><constant>V4L2_EVENT_FRAME_SYNC</constant></entry>
213		    <entry>4</entry>
214		    <entry>
215		      <para>Triggered immediately when the reception of a
216		      frame has begun. This event has a
217		      &v4l2-event-frame-sync; associated with it.</para>
218	
219		      <para>If the hardware needs to be stopped in the case of a
220		      buffer underrun it might not be able to generate this event.
221		      In such cases the <structfield>frame_sequence</structfield>
222		      field in &v4l2-event-frame-sync; will not be incremented. This
223		      causes two consecutive frame sequence numbers to have n times
224		      frame interval in between them.</para>
225		    </entry>
226		  </row>
227		  <row>
228		    <entry><constant>V4L2_EVENT_SOURCE_CHANGE</constant></entry>
229		    <entry>5</entry>
230		    <entry>
231		      <para>This event is triggered when a source parameter change is
232		       detected during runtime by the video device. It can be a
233		       runtime resolution change triggered by a video decoder or the
234		       format change happening on an input connector.
235		       This event requires that the <structfield>id</structfield>
236		       matches the input index (when used with a video device node)
237		       or the pad index (when used with a subdevice node) from which
238		       you want to receive events.</para>
239	
240	              <para>This event has a &v4l2-event-src-change; associated
241		      with it. The <structfield>changes</structfield> bitfield denotes
242		      what has changed for the subscribed pad. If multiple events
243		      occurred before application could dequeue them, then the changes
244		      will have the ORed value of all the events generated.</para>
245		    </entry>
246		  </row>
247		  <row>
248		    <entry><constant>V4L2_EVENT_MOTION_DET</constant></entry>
249		    <entry>6</entry>
250		    <entry>
251		      <para>Triggered whenever the motion detection state for one or more of the regions
252		      changes. This event has a &v4l2-event-motion-det; associated with it.</para>
253		    </entry>
254		  </row>
255		  <row>
256		    <entry><constant>V4L2_EVENT_PRIVATE_START</constant></entry>
257		    <entry>0x08000000</entry>
258		    <entry>Base event number for driver-private events.</entry>
259		  </row>
260		</tbody>
261	      </tgroup>
262	    </table>
263	
264	    <table frame="none" pgwide="1" id="v4l2-event-vsync">
265	      <title>struct <structname>v4l2_event_vsync</structname></title>
266	      <tgroup cols="3">
267		&cs-str;
268		<tbody valign="top">
269		  <row>
270		    <entry>__u8</entry>
271		    <entry><structfield>field</structfield></entry>
272		    <entry>The upcoming field. See &v4l2-field;.</entry>
273		  </row>
274		</tbody>
275	      </tgroup>
276	    </table>
277	
278	    <table frame="none" pgwide="1" id="v4l2-event-ctrl">
279	      <title>struct <structname>v4l2_event_ctrl</structname></title>
280	      <tgroup cols="4">
281		&cs-str;
282		<tbody valign="top">
283		  <row>
284		    <entry>__u32</entry>
285		    <entry><structfield>changes</structfield></entry>
286		    <entry></entry>
287		    <entry>A bitmask that tells what has changed. See <xref linkend="ctrl-changes-flags" />.</entry>
288		  </row>
289		  <row>
290		    <entry>__u32</entry>
291		    <entry><structfield>type</structfield></entry>
292		    <entry></entry>
293		    <entry>The type of the control. See &v4l2-ctrl-type;.</entry>
294		  </row>
295		  <row>
296		    <entry>union (anonymous)</entry>
297		    <entry></entry>
298		    <entry></entry>
299		    <entry></entry>
300		  </row>
301		  <row>
302		    <entry></entry>
303		    <entry>__s32</entry>
304		    <entry><structfield>value</structfield></entry>
305		    <entry>The 32-bit value of the control for 32-bit control types.
306			This is 0 for string controls since the value of a string
307			cannot be passed using &VIDIOC-DQEVENT;.</entry>
308		  </row>
309		  <row>
310		    <entry></entry>
311		    <entry>__s64</entry>
312		    <entry><structfield>value64</structfield></entry>
313		    <entry>The 64-bit value of the control for 64-bit control types.</entry>
314		  </row>
315		  <row>
316		    <entry>__u32</entry>
317		    <entry><structfield>flags</structfield></entry>
318		    <entry></entry>
319		    <entry>The control flags. See <xref linkend="control-flags" />.</entry>
320		  </row>
321		  <row>
322		    <entry>__s32</entry>
323		    <entry><structfield>minimum</structfield></entry>
324		    <entry></entry>
325		    <entry>The minimum value of the control. See &v4l2-queryctrl;.</entry>
326		  </row>
327		  <row>
328		    <entry>__s32</entry>
329		    <entry><structfield>maximum</structfield></entry>
330		    <entry></entry>
331		    <entry>The maximum value of the control. See &v4l2-queryctrl;.</entry>
332		  </row>
333		  <row>
334		    <entry>__s32</entry>
335		    <entry><structfield>step</structfield></entry>
336		    <entry></entry>
337		    <entry>The step value of the control. See &v4l2-queryctrl;.</entry>
338		  </row>
339		  <row>
340		    <entry>__s32</entry>
341		    <entry><structfield>default_value</structfield></entry>
342		    <entry></entry>
343		    <entry>The default value value of the control. See &v4l2-queryctrl;.</entry>
344		  </row>
345		</tbody>
346	      </tgroup>
347	    </table>
348	
349	    <table frame="none" pgwide="1" id="v4l2-event-frame-sync">
350	      <title>struct <structname>v4l2_event_frame_sync</structname></title>
351	      <tgroup cols="3">
352		&cs-str;
353		<tbody valign="top">
354		  <row>
355		    <entry>__u32</entry>
356		    <entry><structfield>frame_sequence</structfield></entry>
357		    <entry>
358		      The sequence number of the frame being received.
359		    </entry>
360		  </row>
361		</tbody>
362	      </tgroup>
363	    </table>
364	
365	    <table frame="none" pgwide="1" id="v4l2-event-src-change">
366	      <title>struct <structname>v4l2_event_src_change</structname></title>
367	      <tgroup cols="3">
368		&cs-str;
369		<tbody valign="top">
370		  <row>
371		    <entry>__u32</entry>
372		    <entry><structfield>changes</structfield></entry>
373		    <entry>
374		      A bitmask that tells what has changed. See <xref linkend="src-changes-flags" />.
375		    </entry>
376		  </row>
377		</tbody>
378	      </tgroup>
379	    </table>
380	
381	    <table frame="none" pgwide="1" id="v4l2-event-motion-det">
382	      <title>struct <structname>v4l2_event_motion_det</structname></title>
383	      <tgroup cols="3">
384		&cs-str;
385		<tbody valign="top">
386		  <row>
387		    <entry>__u32</entry>
388		    <entry><structfield>flags</structfield></entry>
389		    <entry>
390		      Currently only one flag is available: if <constant>V4L2_EVENT_MD_FL_HAVE_FRAME_SEQ</constant>
391		      is set, then the <structfield>frame_sequence</structfield> field is valid,
392		      otherwise that field should be ignored.
393		    </entry>
394		  </row>
395		  <row>
396		    <entry>__u32</entry>
397		    <entry><structfield>frame_sequence</structfield></entry>
398		    <entry>
399		      The sequence number of the frame being received. Only valid if the
400		      <constant>V4L2_EVENT_MD_FL_HAVE_FRAME_SEQ</constant> flag was set.
401		    </entry>
402		  </row>
403		  <row>
404		    <entry>__u32</entry>
405		    <entry><structfield>region_mask</structfield></entry>
406		    <entry>
407		      The bitmask of the regions that reported motion. There is at least one
408		      region. If this field is 0, then no motion was detected at all.
409		      If there is no <constant>V4L2_CID_DETECT_MD_REGION_GRID</constant> control
410		      (see <xref linkend="detect-controls" />) to assign a different region
411		      to each cell in the motion detection grid, then that all cells
412		      are automatically assigned to the default region 0.
413		    </entry>
414		  </row>
415		</tbody>
416	      </tgroup>
417	    </table>
418	
419	    <table pgwide="1" frame="none" id="ctrl-changes-flags">
420	      <title>Control Changes</title>
421	      <tgroup cols="3">
422		&cs-def;
423		<tbody valign="top">
424		  <row>
425		    <entry><constant>V4L2_EVENT_CTRL_CH_VALUE</constant></entry>
426		    <entry>0x0001</entry>
427		    <entry>This control event was triggered because the value of the control
428			changed. Special cases: Volatile controls do no generate this event;
429			If a control has the <constant>V4L2_CTRL_FLAG_EXECUTE_ON_WRITE</constant>
430			flag set, then this event is sent as well, regardless its value.</entry>
431		  </row>
432		  <row>
433		    <entry><constant>V4L2_EVENT_CTRL_CH_FLAGS</constant></entry>
434		    <entry>0x0002</entry>
435		    <entry>This control event was triggered because the control flags
436			changed.</entry>
437		  </row>
438		  <row>
439		    <entry><constant>V4L2_EVENT_CTRL_CH_RANGE</constant></entry>
440		    <entry>0x0004</entry>
441		    <entry>This control event was triggered because the minimum,
442		    maximum, step or the default value of the control changed.</entry>
443		  </row>
444		</tbody>
445	      </tgroup>
446	    </table>
447	
448	    <table pgwide="1" frame="none" id="src-changes-flags">
449	      <title>Source Changes</title>
450	      <tgroup cols="3">
451		&cs-def;
452		<tbody valign="top">
453		  <row>
454		    <entry><constant>V4L2_EVENT_SRC_CH_RESOLUTION</constant></entry>
455		    <entry>0x0001</entry>
456		    <entry>This event gets triggered when a resolution change is
457		    detected at an input. This can come from an input connector or
458		    from a video decoder.
459		    </entry>
460		  </row>
461		</tbody>
462	      </tgroup>
463	    </table>
464	  </refsect1>
465	  <refsect1>
466	    &return-value;
467	  </refsect1>
468	</refentry>
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