linux-vybrid_public/Documentation/DocBook/v4l/vidioc-g-frequency.xml

<refentry id="vidioc-g-frequency">
  <refmeta>
    <refentrytitle>ioctl VIDIOC_G_FREQUENCY, VIDIOC_S_FREQUENCY</refentrytitle>
    &manvol;
  </refmeta>

  <refnamediv>
    <refname>VIDIOC_G_FREQUENCY</refname>
    <refname>VIDIOC_S_FREQUENCY</refname>
    <refpurpose>Get or set tuner or modulator radio
frequency</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_frequency
*<parameter>argp</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
    <funcsynopsis>
      <funcprototype>
	<funcdef>int <function>ioctl</function></funcdef>
	<paramdef>int <parameter>fd</parameter></paramdef>
	<paramdef>int <parameter>request</parameter></paramdef>
	<paramdef>const struct v4l2_frequency
*<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_G_FREQUENCY, VIDIOC_S_FREQUENCY</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>argp</parameter></term>
	<listitem>
	  <para></para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Description</title>

    <para>To get the current tuner or modulator radio frequency
applications set the <structfield>tuner</structfield> field of a
&v4l2-frequency; to the respective tuner or modulator number (only
input devices have tuners, only output devices have modulators), zero
out the <structfield>reserved</structfield> array and
call the <constant>VIDIOC_G_FREQUENCY</constant> ioctl with a pointer
to this structure. The driver stores the current frequency in the
<structfield>frequency</structfield> field.</para>

    <para>To change the current tuner or modulator radio frequency
applications initialize the <structfield>tuner</structfield>,
<structfield>type</structfield> and
<structfield>frequency</structfield> fields, and the
<structfield>reserved</structfield> array of a &v4l2-frequency; and
call the <constant>VIDIOC_S_FREQUENCY</constant> ioctl with a pointer
to this structure. When the requested frequency is not possible the
driver assumes the closest possible value. However
<constant>VIDIOC_S_FREQUENCY</constant> is a write-only ioctl, it does
not return the actual new frequency.</para>

    <table pgwide="1" frame="none" id="v4l2-frequency">
      <title>struct <structname>v4l2_frequency</structname></title>
      <tgroup cols="3">
	&cs-str;
	<tbody valign="top">
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>tuner</structfield></entry>
	    <entry>The tuner or modulator index number. This is the
same value as in the &v4l2-input; <structfield>tuner</structfield>
field and the &v4l2-tuner; <structfield>index</structfield> field, or
the &v4l2-output; <structfield>modulator</structfield> field and the
&v4l2-modulator; <structfield>index</structfield> field.</entry>
	  </row>
	  <row>
	    <entry>&v4l2-tuner-type;</entry>
	    <entry><structfield>type</structfield></entry>
	    <entry>The tuner type. This is the same value as in the
&v4l2-tuner; <structfield>type</structfield> field. The field is not
applicable to modulators, &ie; ignored by drivers.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>frequency</structfield></entry>
	    <entry>Tuning frequency in units of 62.5 kHz, or if the
&v4l2-tuner; or &v4l2-modulator; <structfield>capabilities</structfield> flag
<constant>V4L2_TUNER_CAP_LOW</constant> is set, in units of 62.5
Hz.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>reserved</structfield>[8]</entry>
	    <entry>Reserved for future extensions. Drivers and
	    applications 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 <structfield>tuner</structfield> index is out of
bounds or the value in the <structfield>type</structfield> field is
wrong.</para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>
</refentry>

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