<refentry id="vidioc-g-modulator">
  <refmeta>
    <refentrytitle>ioctl VIDIOC_G_MODULATOR, VIDIOC_S_MODULATOR</refentrytitle>
    &manvol;
  </refmeta>

  <refnamediv>
    <refname>VIDIOC_G_MODULATOR</refname>
    <refname>VIDIOC_S_MODULATOR</refname>
    <refpurpose>Get or set modulator attributes</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_modulator
*<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_modulator
*<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_MODULATOR, VIDIOC_S_MODULATOR</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>argp</parameter></term>
	<listitem>
	  <para></para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Description</title>

    <para>To query the attributes of a modulator applications initialize
the <structfield>index</structfield> field and zero out the
<structfield>reserved</structfield> array of a &v4l2-modulator; and
call the <constant>VIDIOC_G_MODULATOR</constant> ioctl with a pointer
to this structure. Drivers fill the rest of the structure or return an
&EINVAL; when the index is out of bounds. To enumerate all modulators
applications shall begin at index zero, incrementing by one until the
driver returns <errorcode>EINVAL</errorcode>.</para>

    <para>Modulators have two writable properties, an audio
modulation set and the radio frequency. To change the modulated audio
subprograms, applications initialize the <structfield>index
</structfield> and <structfield>txsubchans</structfield> fields and the
<structfield>reserved</structfield> array and call the
<constant>VIDIOC_S_MODULATOR</constant> ioctl. Drivers may choose a
different audio modulation if the request cannot be satisfied. However
this is a write-only ioctl, it does not return the actual audio
modulation selected.</para>

    <para><link linkend="sdr">SDR</link> specific modulator types are
<constant>V4L2_TUNER_SDR</constant> and <constant>V4L2_TUNER_RF</constant>.
For SDR devices <structfield>txsubchans</structfield> field must be
initialized to zero.
The term 'modulator' means SDR transmitter in this context.</para>

    <para>To change the radio frequency the &VIDIOC-S-FREQUENCY; ioctl
is available.</para>

    <table pgwide="1" frame="none" id="v4l2-modulator">
      <title>struct <structname>v4l2_modulator</structname></title>
      <tgroup cols="3">
	&cs-str;
	<tbody valign="top">
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>index</structfield></entry>
	    <entry>Identifies the modulator, set by the
application.</entry>
	  </row>
	  <row>
	    <entry>__u8</entry>
	    <entry><structfield>name</structfield>[32]</entry>
	    <entry>Name of the modulator, a NUL-terminated ASCII
string. This information is intended for the user.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>capability</structfield></entry>
	    <entry>Modulator capability flags. No flags are defined
for this field, the tuner flags in &v4l2-tuner;
are used accordingly. The audio flags indicate the ability
to encode audio subprograms. They will <emphasis>not</emphasis>
change for example with the current video standard.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>rangelow</structfield></entry>
	    <entry>The lowest tunable frequency in units of 62.5
KHz, or if the <structfield>capability</structfield> flag
<constant>V4L2_TUNER_CAP_LOW</constant> is set, in units of 62.5
Hz, or if the <structfield>capability</structfield> flag
<constant>V4L2_TUNER_CAP_1HZ</constant> is set, in units of 1 Hz.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>rangehigh</structfield></entry>
	    <entry>The highest tunable frequency in units of 62.5
KHz, or if the <structfield>capability</structfield> flag
<constant>V4L2_TUNER_CAP_LOW</constant> is set, in units of 62.5
Hz, or if the <structfield>capability</structfield> flag
<constant>V4L2_TUNER_CAP_1HZ</constant> is set, in units of 1 Hz.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>txsubchans</structfield></entry>
	    <entry>With this field applications can determine how
audio sub-carriers shall be modulated. It contains a set of flags as
defined in <xref linkend="modulator-txsubchans" />. Note the tuner
<structfield>rxsubchans</structfield> flags are reused, but the
semantics are different. Video output devices are assumed to have an
analog or PCM audio input with 1-3 channels. The
<structfield>txsubchans</structfield> flags select one or more
channels for modulation, together with some audio subprogram
indicator, for example a stereo pilot tone.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>type</structfield></entry>
	    <entry spanname="hspan">Type of the modulator, see <xref
		linkend="v4l2-tuner-type" />.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>reserved</structfield>[3]</entry>
	    <entry>Reserved for future extensions. Drivers and
applications must set the array to zero.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table pgwide="1" frame="none" id="modulator-txsubchans">
      <title>Modulator Audio Transmission Flags</title>
      <tgroup cols="3">
	&cs-def;
	<tbody valign="top">
	  <row>
	    <entry><constant>V4L2_TUNER_SUB_MONO</constant></entry>
	    <entry>0x0001</entry>
	    <entry>Modulate channel 1 as mono audio, when the input
has more channels, a down-mix of channel 1 and 2. This flag does not
combine with <constant>V4L2_TUNER_SUB_STEREO</constant> or
<constant>V4L2_TUNER_SUB_LANG1</constant>.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_TUNER_SUB_STEREO</constant></entry>
	    <entry>0x0002</entry>
	    <entry>Modulate channel 1 and 2 as left and right
channel of a stereo audio signal. When the input has only one channel
or two channels and <constant>V4L2_TUNER_SUB_SAP</constant> is also
set, channel 1 is encoded as left and right channel. This flag does
not combine with <constant>V4L2_TUNER_SUB_MONO</constant> or
<constant>V4L2_TUNER_SUB_LANG1</constant>. When the driver does not
support stereo audio it shall fall back to mono.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_TUNER_SUB_LANG1</constant></entry>
	    <entry>0x0008</entry>
	    <entry>Modulate channel 1 and 2 as primary and secondary
language of a bilingual audio signal. When the input has only one
channel it is used for both languages. It is not possible to encode
the primary or secondary language only. This flag does not combine
with <constant>V4L2_TUNER_SUB_MONO</constant>,
<constant>V4L2_TUNER_SUB_STEREO</constant> or
<constant>V4L2_TUNER_SUB_SAP</constant>. If the hardware does not
support the respective audio matrix, or the current video standard
does not permit bilingual audio the
<constant>VIDIOC_S_MODULATOR</constant> ioctl shall return an &EINVAL;
and the driver shall fall back to mono or stereo mode.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_TUNER_SUB_LANG2</constant></entry>
	    <entry>0x0004</entry>
	    <entry>Same effect as
<constant>V4L2_TUNER_SUB_SAP</constant>.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_TUNER_SUB_SAP</constant></entry>
	    <entry>0x0004</entry>
	    <entry>When combined with <constant>V4L2_TUNER_SUB_MONO
</constant> the first channel is encoded as mono audio, the last
channel as Second Audio Program. When the input has only one channel
it is used for both audio tracks. When the input has three channels
the mono track is a down-mix of channel 1 and 2. When combined with
<constant>V4L2_TUNER_SUB_STEREO</constant> channel 1 and 2 are
encoded as left and right stereo audio, channel 3 as Second Audio
Program. When the input has only two channels, the first is encoded as
left and right channel and the second as SAP. When the input has only
one channel it is used for all audio tracks. It is not possible to
encode a Second Audio Program only. This flag must combine with
<constant>V4L2_TUNER_SUB_MONO</constant> or
<constant>V4L2_TUNER_SUB_STEREO</constant>. If the hardware does not
support the respective audio matrix, or the current video standard
does not permit SAP the <constant>VIDIOC_S_MODULATOR</constant> ioctl
shall return an &EINVAL; and driver shall fall back to mono or stereo
mode.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_TUNER_SUB_RDS</constant></entry>
	    <entry>0x0010</entry>
	    <entry>Enable the RDS encoder for a radio FM transmitter.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>
  </refsect1>

  <refsect1>
    &return-value;

    <variablelist>
      <varlistentry>
	<term><errorcode>EINVAL</errorcode></term>
	<listitem>
	  <para>The &v4l2-modulator;
<structfield>index</structfield> is out of bounds.</para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>
</refentry>