Documentation/DocBook/media/v4l/cec-ioc-dqevent.xml

<refentry id="cec-ioc-g-event">
  <refmeta>
    <refentrytitle>ioctl CEC_DQEVENT</refentrytitle>
    &manvol;
  </refmeta>

  <refnamediv>
    <refname>CEC_DQEVENT</refname>
    <refpurpose>Dequeue a CEC event</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <funcsynopsis>
      <funcprototype>
	<funcdef>int <function>ioctl</function></funcdef>
	<paramdef>int <parameter>fd</parameter></paramdef>
	<paramdef>int <parameter>request</parameter></paramdef>
	<paramdef>struct cec_event *<parameter>argp</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Arguments</title>

    <variablelist>
      <varlistentry>
	<term><parameter>fd</parameter></term>
	<listitem>
	  <para>File descriptor returned by
	  <link linkend='cec-func-open'><function>open()</function></link>.</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>request</parameter></term>
	<listitem>
	  <para>CEC_DQEVENT</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>argp</parameter></term>
	<listitem>
	  <para></para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Description</title>

    <para>
      Note: this documents the proposed CEC API. This API is not yet finalized and
      is currently only available as a staging kernel module.
    </para>

    <para>CEC devices can send asynchronous events. These can be retrieved by calling
    the <constant>CEC_DQEVENT</constant> ioctl. If the file descriptor is in non-blocking
    mode and no event is pending, then it will return -1 and set errno to the &EAGAIN;.</para>

    <para>The internal event queues are per-filehandle and per-event type. If there is
    no more room in a queue then the last event is overwritten with the new one. This
    means that intermediate results can be thrown away but that the latest event is always
    available. This also means that is it possible to read two successive events that have
    the same value (e.g. two CEC_EVENT_STATE_CHANGE events with the same state). In that
    case the intermediate state changes were lost but it is guaranteed that the state
    did change in between the two events.</para>

    <table pgwide="1" frame="none" id="cec-event-state-change">
      <title>struct <structname>cec_event_state_change</structname></title>
      <tgroup cols="3">
	&cs-str;
	<tbody valign="top">
	  <row>
	    <entry>__u16</entry>
	    <entry><structfield>phys_addr</structfield></entry>
	    <entry>The current physical address.</entry>
	  </row>
	  <row>
	    <entry>__u16</entry>
	    <entry><structfield>log_addr_mask</structfield></entry>
	    <entry>The current set of claimed logical addresses.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table pgwide="1" frame="none" id="cec-event-lost-msgs">
      <title>struct <structname>cec_event_lost_msgs</structname></title>
      <tgroup cols="3">
	&cs-str;
	<tbody valign="top">
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>lost_msgs</structfield></entry>
	    <entry>Set to the number of lost messages since the filehandle
	    was opened or since the last time this event was dequeued for
	    this filehandle. The messages lost are the oldest messages. So
	    when a new message arrives and there is no more room, then the
	    oldest message is discarded to make room for the new one. The
	    internal size of the message queue guarantees that all messages
	    received in the last two seconds will be stored. Since messages
	    should be replied to within a second according to the CEC
	    specification, this is more than enough.
	    </entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table pgwide="1" frame="none" id="cec-event">
      <title>struct <structname>cec_event</structname></title>
      <tgroup cols="4">
	&cs-str;
	<tbody valign="top">
	  <row>
	    <entry>__u64</entry>
	    <entry><structfield>ts</structfield></entry>
	    <entry>Timestamp of the event in ns.</entry>
	    <entry></entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>event</structfield></entry>
	    <entry>The CEC event type, see <xref linkend="cec-events" />.</entry>
	    <entry></entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>flags</structfield></entry>
	    <entry>Event flags, see <xref linkend="cec-event-flags" />.</entry>
	    <entry></entry>
	  </row>
	  <row>
	    <entry>union</entry>
	    <entry>(anonymous)</entry>
	    <entry></entry>
	    <entry></entry>
	  </row>
	  <row>
	    <entry></entry>
	    <entry>struct cec_event_state_change</entry>
	    <entry><structfield>state_change</structfield></entry>
	    <entry>The new adapter state as sent by the <constant>CEC_EVENT_STATE_CHANGE</constant>
	    event.</entry>
	  </row>
	  <row>
	    <entry></entry>
	    <entry>struct cec_event_lost_msgs</entry>
	    <entry><structfield>lost_msgs</structfield></entry>
	    <entry>The number of lost messages as sent by the <constant>CEC_EVENT_LOST_MSGS</constant>
	    event.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table pgwide="1" frame="none" id="cec-events">
      <title>CEC Events Types</title>
      <tgroup cols="3">
	&cs-def;
	<tbody valign="top">
	  <row>
	    <entry><constant>CEC_EVENT_STATE_CHANGE</constant></entry>
	    <entry>1</entry>
	    <entry>Generated when the CEC Adapter's state changes. When open() is
	    called an initial event will be generated for that filehandle with the
	    CEC Adapter's state at that time.
	    </entry>
	  </row>
	  <row>
	    <entry><constant>CEC_EVENT_LOST_MSGS</constant></entry>
	    <entry>2</entry>
	    <entry>Generated if one or more CEC messages were lost because the
	    application didn't dequeue CEC messages fast enough.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table pgwide="1" frame="none" id="cec-event-flags">
      <title>CEC Event Flags</title>
      <tgroup cols="3">
	&cs-def;
	<tbody valign="top">
	  <row>
	    <entry><constant>CEC_EVENT_FL_INITIAL_VALUE</constant></entry>
	    <entry>1</entry>
	    <entry>Set for the initial events that are generated when the device is
	    opened. See the table above for which events do this. This allows
	    applications to learn the initial state of the CEC adapter at open()
	    time.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>
  </refsect1>

  <refsect1>
    &return-value;
  </refsect1>
</refentry>