Documentation/DocBook/media/v4l/vidioc-dqevent.xml

   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>