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.</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 V4L2_EVENT_VSYNC.
  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 V4L2_EVENT_CTRL.
  87             </entry>
  88           </row>
  89           <row>
  90             <entry></entry>
  91             <entry>&v4l2-event-frame-sync;</entry>
  92             <entry><structfield>frame</structfield></entry>
  93             <entry>Event data for event V4L2_EVENT_FRAME_SYNC.</entry>
  94           </row>
  95           <row>
  96             <entry></entry>
  97             <entry>__u8</entry>
  98             <entry><structfield>data</structfield>[64]</entry>
  99             <entry>Event data. Defined by the event type. The union
 100             should be used to define easily accessible type for
 101             events.</entry>
 102           </row>
 103           <row>
 104             <entry>__u32</entry>
 105             <entry><structfield>pending</structfield></entry>
 106             <entry></entry>
 107             <entry>Number of pending events excluding this one.</entry>
 108           </row>
 109           <row>
 110             <entry>__u32</entry>
 111             <entry><structfield>sequence</structfield></entry>
 112             <entry></entry>
 113             <entry>Event sequence number. The sequence number is
 114             incremented for every subscribed event that takes place.
 115             If sequence numbers are not contiguous it means that
 116             events have been lost.
 117             </entry>
 118           </row>
 119           <row>
 120             <entry>struct timespec</entry>
 121             <entry><structfield>timestamp</structfield></entry>
 122             <entry></entry>
 123             <entry>Event timestamp.</entry>
 124           </row>
 125           <row>
 126             <entry>u32</entry>
 127             <entry><structfield>id</structfield></entry>
 128             <entry></entry>
 129             <entry>The ID associated with the event source. If the event does not
 130                 have an associated ID (this depends on the event type), then this
 131                 is 0.</entry>
 132           </row>
 133           <row>
 134             <entry>__u32</entry>
 135             <entry><structfield>reserved</structfield>[8]</entry>
 136             <entry></entry>
 137             <entry>Reserved for future extensions. Drivers must set
 138             the array to zero.</entry>
 139           </row>
 140         </tbody>
 141       </tgroup>
 142     </table>
 143
 144     <table frame="none" pgwide="1" id="v4l2-event-vsync">
 145       <title>struct <structname>v4l2_event_vsync</structname></title>
 146       <tgroup cols="3">
 147         &cs-str;
 148         <tbody valign="top">
 149           <row>
 150             <entry>__u8</entry>
 151             <entry><structfield>field</structfield></entry>
 152             <entry>The upcoming field. See &v4l2-field;.</entry>
 153           </row>
 154         </tbody>
 155       </tgroup>
 156     </table>
 157
 158     <table frame="none" pgwide="1" id="v4l2-event-ctrl">
 159       <title>struct <structname>v4l2_event_ctrl</structname></title>
 160       <tgroup cols="4">
 161         &cs-str;
 162         <tbody valign="top">
 163           <row>
 164             <entry>__u32</entry>
 165             <entry><structfield>changes</structfield></entry>
 166             <entry></entry>
 167             <entry>A bitmask that tells what has changed. See <xref linkend="changes-flags" />.</entry>
 168           </row>
 169           <row>
 170             <entry>__u32</entry>
 171             <entry><structfield>type</structfield></entry>
 172             <entry></entry>
 173             <entry>The type of the control. See &v4l2-ctrl-type;.</entry>
 174           </row>
 175           <row>
 176             <entry>union (anonymous)</entry>
 177             <entry></entry>
 178             <entry></entry>
 179             <entry></entry>
 180           </row>
 181           <row>
 182             <entry></entry>
 183             <entry>__s32</entry>
 184             <entry><structfield>value</structfield></entry>
 185             <entry>The 32-bit value of the control for 32-bit control types.
 186                 This is 0 for string controls since the value of a string
 187                 cannot be passed using &VIDIOC-DQEVENT;.</entry>
 188           </row>
 189           <row>
 190             <entry></entry>
 191             <entry>__s64</entry>
 192             <entry><structfield>value64</structfield></entry>
 193             <entry>The 64-bit value of the control for 64-bit control types.</entry>
 194           </row>
 195           <row>
 196             <entry>__u32</entry>
 197             <entry><structfield>flags</structfield></entry>
 198             <entry></entry>
 199             <entry>The control flags. See <xref linkend="control-flags" />.</entry>
 200           </row>
 201           <row>
 202             <entry>__s32</entry>
 203             <entry><structfield>minimum</structfield></entry>
 204             <entry></entry>
 205             <entry>The minimum value of the control. See &v4l2-queryctrl;.</entry>
 206           </row>
 207           <row>
 208             <entry>__s32</entry>
 209             <entry><structfield>maximum</structfield></entry>
 210             <entry></entry>
 211             <entry>The maximum value of the control. See &v4l2-queryctrl;.</entry>
 212           </row>
 213           <row>
 214             <entry>__s32</entry>
 215             <entry><structfield>step</structfield></entry>
 216             <entry></entry>
 217             <entry>The step value of the control. See &v4l2-queryctrl;.</entry>
 218           </row>
 219           <row>
 220             <entry>__s32</entry>
 221             <entry><structfield>default_value</structfield></entry>
 222             <entry></entry>
 223             <entry>The default value value of the control. See &v4l2-queryctrl;.</entry>
 224           </row>
 225         </tbody>
 226       </tgroup>
 227     </table>
 228
 229     <table frame="none" pgwide="1" id="v4l2-event-frame-sync">
 230       <title>struct <structname>v4l2_event_frame_sync</structname></title>
 231       <tgroup cols="3">
 232         &cs-str;
 233         <tbody valign="top">
 234           <row>
 235             <entry>__u32</entry>
 236             <entry><structfield>frame_sequence</structfield></entry>
 237             <entry>
 238               The sequence number of the frame being received.
 239             </entry>
 240           </row>
 241         </tbody>
 242       </tgroup>
 243     </table>
 244
 245     <table pgwide="1" frame="none" id="changes-flags">
 246       <title>Changes</title>
 247       <tgroup cols="3">
 248         &cs-def;
 249         <tbody valign="top">
 250           <row>
 251             <entry><constant>V4L2_EVENT_CTRL_CH_VALUE</constant></entry>
 252             <entry>0x0001</entry>
 253             <entry>This control event was triggered because the value of the control
 254                 changed. Special case: if a button control is pressed, then this
 255                 event is sent as well, even though there is not explicit value
 256                 associated with a button control.</entry>
 257           </row>
 258           <row>
 259             <entry><constant>V4L2_EVENT_CTRL_CH_FLAGS</constant></entry>
 260             <entry>0x0002</entry>
 261             <entry>This control event was triggered because the control flags
 262                 changed.</entry>
 263           </row>
 264         </tbody>
 265       </tgroup>
 266     </table>
 267   </refsect1>
 268   <refsect1>
 269     &return-value;
 270   </refsect1>
 271 </refentry>