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. The timestamp has been taken from the
137	    <constant>CLOCK_MONOTONIC</constant> clock. To access the
138	    same clock outside V4L2, use <function>clock_gettime(2)</function>.
139	    </entry>
140	  </row>
141	  <row>
142	    <entry>u32</entry>
143	    <entry><structfield>id</structfield></entry>
144            <entry></entry>
145	    <entry>The ID associated with the event source. If the event does not
146		have an associated ID (this depends on the event type), then this
147		is 0.</entry>
148	  </row>
149	  <row>
150	    <entry>__u32</entry>
151	    <entry><structfield>reserved</structfield>[8]</entry>
152            <entry></entry>
153	    <entry>Reserved for future extensions. Drivers must set
154	    the array to zero.</entry>
155	  </row>
156	</tbody>
157      </tgroup>
158    </table>
159
160    <table frame="none" pgwide="1" id="event-type">
161      <title>Event Types</title>
162      <tgroup cols="3">
163	&cs-def;
164	<tbody valign="top">
165	  <row>
166	    <entry><constant>V4L2_EVENT_ALL</constant></entry>
167	    <entry>0</entry>
168	    <entry>All events. V4L2_EVENT_ALL is valid only for
169	    VIDIOC_UNSUBSCRIBE_EVENT for unsubscribing all events at once.
170	    </entry>
171	  </row>
172	  <row>
173	    <entry><constant>V4L2_EVENT_VSYNC</constant></entry>
174	    <entry>1</entry>
175	    <entry>This event is triggered on the vertical sync.
176	    This event has a &v4l2-event-vsync; associated with it.
177	    </entry>
178	  </row>
179	  <row>
180	    <entry><constant>V4L2_EVENT_EOS</constant></entry>
181	    <entry>2</entry>
182	    <entry>This event is triggered when the end of a stream is reached.
183	    This is typically used with MPEG decoders to report to the application
184	    when the last of the MPEG stream has been decoded.
185	    </entry>
186	  </row>
187	  <row>
188	    <entry><constant>V4L2_EVENT_CTRL</constant></entry>
189	    <entry>3</entry>
190	    <entry><para>This event requires that the <structfield>id</structfield>
191		matches the control ID from which you want to receive events.
192		This event is triggered if the control's value changes, if a
193		button control is pressed or if the control's flags change.
194	    	This event has a &v4l2-event-ctrl; associated with it. This struct
195		contains much of the same information as &v4l2-queryctrl; and
196		&v4l2-control;.</para>
197
198		<para>If the event is generated due to a call to &VIDIOC-S-CTRL; or
199		&VIDIOC-S-EXT-CTRLS;, then the event will <emphasis>not</emphasis> be sent to
200		the file handle that called the ioctl function. This prevents
201		nasty feedback loops. If you <emphasis>do</emphasis> want to get the
202		event, then set the <constant>V4L2_EVENT_SUB_FL_ALLOW_FEEDBACK</constant>
203		flag.
204		</para>
205
206		<para>This event type will ensure that no information is lost when
207		more events are raised than there is room internally. In that
208		case the &v4l2-event-ctrl; of the second-oldest event is kept,
209		but the <structfield>changes</structfield> field of the
210		second-oldest event is ORed with the <structfield>changes</structfield>
211		field of the oldest event.</para>
212	    </entry>
213	  </row>
214	  <row>
215	    <entry><constant>V4L2_EVENT_FRAME_SYNC</constant></entry>
216	    <entry>4</entry>
217	    <entry>
218	      <para>Triggered immediately when the reception of a
219	      frame has begun. This event has a
220	      &v4l2-event-frame-sync; associated with it.</para>
221
222	      <para>If the hardware needs to be stopped in the case of a
223	      buffer underrun it might not be able to generate this event.
224	      In such cases the <structfield>frame_sequence</structfield>
225	      field in &v4l2-event-frame-sync; will not be incremented. This
226	      causes two consecutive frame sequence numbers to have n times
227	      frame interval in between them.</para>
228	    </entry>
229	  </row>
230	  <row>
231	    <entry><constant>V4L2_EVENT_SOURCE_CHANGE</constant></entry>
232	    <entry>5</entry>
233	    <entry>
234	      <para>This event is triggered when a source parameter change is
235	       detected during runtime by the video device. It can be a
236	       runtime resolution change triggered by a video decoder or the
237	       format change happening on an input connector.
238	       This event requires that the <structfield>id</structfield>
239	       matches the input index (when used with a video device node)
240	       or the pad index (when used with a subdevice node) from which
241	       you want to receive events.</para>
242
243              <para>This event has a &v4l2-event-src-change; associated
244	      with it. The <structfield>changes</structfield> bitfield denotes
245	      what has changed for the subscribed pad. If multiple events
246	      occurred before application could dequeue them, then the changes
247	      will have the ORed value of all the events generated.</para>
248	    </entry>
249	  </row>
250	  <row>
251	    <entry><constant>V4L2_EVENT_MOTION_DET</constant></entry>
252	    <entry>6</entry>
253	    <entry>
254	      <para>Triggered whenever the motion detection state for one or more of the regions
255	      changes. This event has a &v4l2-event-motion-det; associated with it.</para>
256	    </entry>
257	  </row>
258	  <row>
259	    <entry><constant>V4L2_EVENT_PRIVATE_START</constant></entry>
260	    <entry>0x08000000</entry>
261	    <entry>Base event number for driver-private events.</entry>
262	  </row>
263	</tbody>
264      </tgroup>
265    </table>
266
267    <table frame="none" pgwide="1" id="v4l2-event-vsync">
268      <title>struct <structname>v4l2_event_vsync</structname></title>
269      <tgroup cols="3">
270	&cs-str;
271	<tbody valign="top">
272	  <row>
273	    <entry>__u8</entry>
274	    <entry><structfield>field</structfield></entry>
275	    <entry>The upcoming field. See &v4l2-field;.</entry>
276	  </row>
277	</tbody>
278      </tgroup>
279    </table>
280
281    <table frame="none" pgwide="1" id="v4l2-event-ctrl">
282      <title>struct <structname>v4l2_event_ctrl</structname></title>
283      <tgroup cols="4">
284	&cs-str;
285	<tbody valign="top">
286	  <row>
287	    <entry>__u32</entry>
288	    <entry><structfield>changes</structfield></entry>
289	    <entry></entry>
290	    <entry>A bitmask that tells what has changed. See <xref linkend="ctrl-changes-flags" />.</entry>
291	  </row>
292	  <row>
293	    <entry>__u32</entry>
294	    <entry><structfield>type</structfield></entry>
295	    <entry></entry>
296	    <entry>The type of the control. See &v4l2-ctrl-type;.</entry>
297	  </row>
298	  <row>
299	    <entry>union (anonymous)</entry>
300	    <entry></entry>
301	    <entry></entry>
302	    <entry></entry>
303	  </row>
304	  <row>
305	    <entry></entry>
306	    <entry>__s32</entry>
307	    <entry><structfield>value</structfield></entry>
308	    <entry>The 32-bit value of the control for 32-bit control types.
309		This is 0 for string controls since the value of a string
310		cannot be passed using &VIDIOC-DQEVENT;.</entry>
311	  </row>
312	  <row>
313	    <entry></entry>
314	    <entry>__s64</entry>
315	    <entry><structfield>value64</structfield></entry>
316	    <entry>The 64-bit value of the control for 64-bit control types.</entry>
317	  </row>
318	  <row>
319	    <entry>__u32</entry>
320	    <entry><structfield>flags</structfield></entry>
321	    <entry></entry>
322	    <entry>The control flags. See <xref linkend="control-flags" />.</entry>
323	  </row>
324	  <row>
325	    <entry>__s32</entry>
326	    <entry><structfield>minimum</structfield></entry>
327	    <entry></entry>
328	    <entry>The minimum value of the control. See &v4l2-queryctrl;.</entry>
329	  </row>
330	  <row>
331	    <entry>__s32</entry>
332	    <entry><structfield>maximum</structfield></entry>
333	    <entry></entry>
334	    <entry>The maximum value of the control. See &v4l2-queryctrl;.</entry>
335	  </row>
336	  <row>
337	    <entry>__s32</entry>
338	    <entry><structfield>step</structfield></entry>
339	    <entry></entry>
340	    <entry>The step value of the control. See &v4l2-queryctrl;.</entry>
341	  </row>
342	  <row>
343	    <entry>__s32</entry>
344	    <entry><structfield>default_value</structfield></entry>
345	    <entry></entry>
346	    <entry>The default value value of the control. See &v4l2-queryctrl;.</entry>
347	  </row>
348	</tbody>
349      </tgroup>
350    </table>
351
352    <table frame="none" pgwide="1" id="v4l2-event-frame-sync">
353      <title>struct <structname>v4l2_event_frame_sync</structname></title>
354      <tgroup cols="3">
355	&cs-str;
356	<tbody valign="top">
357	  <row>
358	    <entry>__u32</entry>
359	    <entry><structfield>frame_sequence</structfield></entry>
360	    <entry>
361	      The sequence number of the frame being received.
362	    </entry>
363	  </row>
364	</tbody>
365      </tgroup>
366    </table>
367
368    <table frame="none" pgwide="1" id="v4l2-event-src-change">
369      <title>struct <structname>v4l2_event_src_change</structname></title>
370      <tgroup cols="3">
371	&cs-str;
372	<tbody valign="top">
373	  <row>
374	    <entry>__u32</entry>
375	    <entry><structfield>changes</structfield></entry>
376	    <entry>
377	      A bitmask that tells what has changed. See <xref linkend="src-changes-flags" />.
378	    </entry>
379	  </row>
380	</tbody>
381      </tgroup>
382    </table>
383
384    <table frame="none" pgwide="1" id="v4l2-event-motion-det">
385      <title>struct <structname>v4l2_event_motion_det</structname></title>
386      <tgroup cols="3">
387	&cs-str;
388	<tbody valign="top">
389	  <row>
390	    <entry>__u32</entry>
391	    <entry><structfield>flags</structfield></entry>
392	    <entry>
393	      Currently only one flag is available: if <constant>V4L2_EVENT_MD_FL_HAVE_FRAME_SEQ</constant>
394	      is set, then the <structfield>frame_sequence</structfield> field is valid,
395	      otherwise that field should be ignored.
396	    </entry>
397	  </row>
398	  <row>
399	    <entry>__u32</entry>
400	    <entry><structfield>frame_sequence</structfield></entry>
401	    <entry>
402	      The sequence number of the frame being received. Only valid if the
403	      <constant>V4L2_EVENT_MD_FL_HAVE_FRAME_SEQ</constant> flag was set.
404	    </entry>
405	  </row>
406	  <row>
407	    <entry>__u32</entry>
408	    <entry><structfield>region_mask</structfield></entry>
409	    <entry>
410	      The bitmask of the regions that reported motion. There is at least one
411	      region. If this field is 0, then no motion was detected at all.
412	      If there is no <constant>V4L2_CID_DETECT_MD_REGION_GRID</constant> control
413	      (see <xref linkend="detect-controls" />) to assign a different region
414	      to each cell in the motion detection grid, then that all cells
415	      are automatically assigned to the default region 0.
416	    </entry>
417	  </row>
418	</tbody>
419      </tgroup>
420    </table>
421
422    <table pgwide="1" frame="none" id="ctrl-changes-flags">
423      <title>Control Changes</title>
424      <tgroup cols="3">
425	&cs-def;
426	<tbody valign="top">
427	  <row>
428	    <entry><constant>V4L2_EVENT_CTRL_CH_VALUE</constant></entry>
429	    <entry>0x0001</entry>
430	    <entry>This control event was triggered because the value of the control
431		changed. Special cases: Volatile controls do no generate this event;
432		If a control has the <constant>V4L2_CTRL_FLAG_EXECUTE_ON_WRITE</constant>
433		flag set, then this event is sent as well, regardless its value.</entry>
434	  </row>
435	  <row>
436	    <entry><constant>V4L2_EVENT_CTRL_CH_FLAGS</constant></entry>
437	    <entry>0x0002</entry>
438	    <entry>This control event was triggered because the control flags
439		changed.</entry>
440	  </row>
441	  <row>
442	    <entry><constant>V4L2_EVENT_CTRL_CH_RANGE</constant></entry>
443	    <entry>0x0004</entry>
444	    <entry>This control event was triggered because the minimum,
445	    maximum, step or the default value of the control changed.</entry>
446	  </row>
447	</tbody>
448      </tgroup>
449    </table>
450
451    <table pgwide="1" frame="none" id="src-changes-flags">
452      <title>Source Changes</title>
453      <tgroup cols="3">
454	&cs-def;
455	<tbody valign="top">
456	  <row>
457	    <entry><constant>V4L2_EVENT_SRC_CH_RESOLUTION</constant></entry>
458	    <entry>0x0001</entry>
459	    <entry>This event gets triggered when a resolution change is
460	    detected at an input. This can come from an input connector or
461	    from a video decoder.
462	    </entry>
463	  </row>
464	</tbody>
465      </tgroup>
466    </table>
467  </refsect1>
468  <refsect1>
469    &return-value;
470  </refsect1>
471</refentry>
472