CooCenter-System-kernel/Documentation/DocBook/media/v4l/vidioc-enum-freq-bands.xml

<refentry id="vidioc-enum-freq-bands">
  <refmeta>
    <refentrytitle>ioctl VIDIOC_ENUM_FREQ_BANDS</refentrytitle>
    &manvol;
  </refmeta>

  <refnamediv>
    <refname>VIDIOC_ENUM_FREQ_BANDS</refname>
    <refpurpose>Enumerate supported frequency bands</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_band
*<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_ENUM_FREQ_BANDS</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>Enumerates the frequency bands that a tuner or modulator supports.
To do this applications initialize the <structfield>tuner</structfield>,
<structfield>type</structfield> and <structfield>index</structfield> fields,
and zero out the <structfield>reserved</structfield> array of a &v4l2-frequency-band; and
call the <constant>VIDIOC_ENUM_FREQ_BANDS</constant> ioctl with a pointer
to this structure.</para>

    <para>This ioctl is supported if the <constant>V4L2_TUNER_CAP_FREQ_BANDS</constant> capability
    of the corresponding tuner/modulator is set.</para>

    <table pgwide="1" frame="none" id="v4l2-frequency-band">
      <title>struct <structname>v4l2_frequency_band</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>__u32</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 type must be set
to <constant>V4L2_TUNER_RADIO</constant> for <filename>/dev/radioX</filename>
device nodes, and to <constant>V4L2_TUNER_ANALOG_TV</constant>
for all others. Set this field to <constant>V4L2_TUNER_RADIO</constant> for
modulators (currently only radio modulators are supported).
See <xref linkend="v4l2-tuner-type" /></entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>index</structfield></entry>
	    <entry>Identifies the frequency band, set by the application.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>capability</structfield></entry>
	    <entry spanname="hspan">The tuner/modulator capability flags for
this frequency band, see <xref linkend="tuner-capability" />. The <constant>V4L2_TUNER_CAP_LOW</constant>
or <constant>V4L2_TUNER_CAP_1HZ</constant> capability must be the same for all frequency bands of the selected tuner/modulator.
So either all bands have that capability set, or none of them have that capability.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>rangelow</structfield></entry>
	    <entry spanname="hspan">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, for this frequency band. A 1 Hz unit is used when the <structfield>capability</structfield> flag
<constant>V4L2_TUNER_CAP_1HZ</constant> is set.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>rangehigh</structfield></entry>
	    <entry spanname="hspan">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, for this frequency band. A 1 Hz unit is used when the <structfield>capability</structfield> flag
<constant>V4L2_TUNER_CAP_1HZ</constant> is set.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>modulation</structfield></entry>
	    <entry spanname="hspan">The supported modulation systems of this frequency band.
	    See <xref linkend="band-modulation" />. Note that currently only one
	    modulation system per frequency band is supported. More work will need to
	    be done if multiple modulation systems are possible. Contact the
	    linux-media mailing list (&v4l-ml;) if you need that functionality.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>reserved</structfield>[9]</entry>
	    <entry>Reserved for future extensions. Applications and drivers
	    must set the array to zero.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table pgwide="1" frame="none" id="band-modulation">
      <title>Band Modulation Systems</title>
      <tgroup cols="3">
	&cs-def;
	<tbody valign="top">
	  <row>
	    <entry><constant>V4L2_BAND_MODULATION_VSB</constant></entry>
	    <entry>0x02</entry>
	    <entry>Vestigial Sideband modulation, used for analog TV.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_BAND_MODULATION_FM</constant></entry>
	    <entry>0x04</entry>
	    <entry>Frequency Modulation, commonly used for analog radio.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_BAND_MODULATION_AM</constant></entry>
	    <entry>0x08</entry>
	    <entry>Amplitude Modulation, commonly used for analog radio.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>
  </refsect1>

  <refsect1>
    &return-value;

    <variablelist>
      <varlistentry>
	<term><errorcode>EINVAL</errorcode></term>
	<listitem>
	  <para>The <structfield>tuner</structfield> or <structfield>index</structfield>
is out of bounds or the <structfield>type</structfield> field is wrong.</para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>
</refentry>