CooCenter-System-kernel/Documentation/DocBook/media/v4l/vidioc-subdev-enum-frame-interval.xml

<refentry id="vidioc-subdev-enum-frame-interval">
  <refmeta>
    <refentrytitle>ioctl VIDIOC_SUBDEV_ENUM_FRAME_INTERVAL</refentrytitle>
    &manvol;
  </refmeta>

  <refnamediv>
    <refname>VIDIOC_SUBDEV_ENUM_FRAME_INTERVAL</refname>
    <refpurpose>Enumerate frame intervals</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 v4l2_subdev_frame_interval_enum *
	<parameter>argp</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Arguments</title>

    <variablelist>
      <varlistentry>
	<term><parameter>fd</parameter></term>
	<listitem>
	  <para>&fd;</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>request</parameter></term>
	<listitem>
	  <para>VIDIOC_SUBDEV_ENUM_FRAME_INTERVAL</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>argp</parameter></term>
	<listitem>
	  <para></para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Description</title>

    <note>
      <title>Experimental</title>
      <para>This is an <link linkend="experimental">experimental</link>
      interface and may change in the future.</para>
    </note>

    <para>This ioctl lets applications enumerate available frame intervals on a
    given sub-device pad. Frame intervals only makes sense for sub-devices that
    can control the frame period on their own. This includes, for instance,
    image sensors and TV tuners.</para>

    <para>For the common use case of image sensors, the frame intervals
    available on the sub-device output pad depend on the frame format and size
    on the same pad. Applications must thus specify the desired format and size
    when enumerating frame intervals.</para>

    <para>To enumerate frame intervals applications initialize the
    <structfield>index</structfield>, <structfield>pad</structfield>,
    <structfield>which</structfield>, <structfield>code</structfield>,
    <structfield>width</structfield> and <structfield>height</structfield>
    fields of &v4l2-subdev-frame-interval-enum; and call the
    <constant>VIDIOC_SUBDEV_ENUM_FRAME_INTERVAL</constant> ioctl with a pointer
    to this structure. Drivers fill the rest of the structure or return
    an &EINVAL; if one of the input fields is invalid. All frame intervals are
    enumerable by beginning at index zero and incrementing by one until
    <errorcode>EINVAL</errorcode> is returned.</para>

    <para>Available frame intervals may depend on the current 'try' formats
    at other pads of the sub-device, as well as on the current active links. See
    &VIDIOC-SUBDEV-G-FMT; for more information about the try formats.</para>

    <para>Sub-devices that support the frame interval enumeration ioctl should
    implemented it on a single pad only. Its behaviour when supported on
    multiple pads of the same sub-device is not defined.</para>

    <table pgwide="1" frame="none" id="v4l2-subdev-frame-interval-enum">
      <title>struct <structname>v4l2_subdev_frame_interval_enum</structname></title>
      <tgroup cols="3">
	&cs-str;
	<tbody valign="top">
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>index</structfield></entry>
	    <entry>Number of the format in the enumeration, set by the
	    application.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>pad</structfield></entry>
	    <entry>Pad number as reported by the media controller API.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>code</structfield></entry>
	    <entry>The media bus format code, as defined in
	    <xref linkend="v4l2-mbus-format" />.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>width</structfield></entry>
	    <entry>Frame width, in pixels.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>height</structfield></entry>
	    <entry>Frame height, in pixels.</entry>
	  </row>
	  <row>
	    <entry>&v4l2-fract;</entry>
	    <entry><structfield>interval</structfield></entry>
	    <entry>Period, in seconds, between consecutive video frames.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>which</structfield></entry>
	    <entry>Frame intervals to be enumerated, from &v4l2-subdev-format-whence;.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>reserved</structfield>[8]</entry>
	    <entry>Reserved for future extensions. Applications and drivers must
	    set the array to zero.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>
  </refsect1>

  <refsect1>
    &return-value;

    <variablelist>
      <varlistentry>
	<term><errorcode>EINVAL</errorcode></term>
	<listitem>
	  <para>The &v4l2-subdev-frame-interval-enum;
	  <structfield>pad</structfield> references a non-existing pad, one of
	  the <structfield>code</structfield>, <structfield>width</structfield>
	  or <structfield>height</structfield> fields are invalid for the given
	  pad or the <structfield>index</structfield> field is out of bounds.
	  </para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>
</refentry>