Based on kernel version 4.7.2. Page generated on 2016-08-22 22:45 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. 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>
