kernel/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.</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>