| blob | 50ccd33948c1cbee6fb8bbd28864681780c1b833 |
1 <refentry id="vidioc-dqevent">
2 <refmeta>
3 <refentrytitle>ioctl VIDIOC_DQEVENT</refentrytitle>
4 &manvol;
5 </refmeta>
7 <refnamediv>
8 <refname>VIDIOC_DQEVENT</refname>
9 <refpurpose>Dequeue event</refpurpose>
10 </refnamediv>
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>
24 <refsect1>
25 <title>Arguments</title>
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>
49 <refsect1>
50 <title>Description</title>
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>
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>
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>
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>
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>
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>
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>
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>
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>
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>
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>
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>
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>
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>