Documentation/DocBook/media/v4l/dev-rds.xml - maze/linux - Git at Google

      <title>RDS Interface</title>

       <para>The Radio Data System transmits supplementary
 information in binary format, for example the station name or travel
 information, on an inaudible audio subcarrier of a radio program. This
 interface is aimed at devices capable of receiving and/or transmitting RDS
 information.</para>

       <para>For more information see the core RDS standard <xref linkend="en50067" />
 and the RBDS standard <xref linkend="nrsc4" />.</para>

       <para>Note that the RBDS standard as is used in the USA is almost identical
 to the RDS standard. Any RDS decoder/encoder can also handle RBDS. Only some of the
 fields have slightly different meanings. See the RBDS standard for more
 information.</para>

       <para>The RBDS standard also specifies support for MMBS (Modified Mobile Search).
 This is a proprietary format which seems to be discontinued. The RDS interface does not
 support this format. Should support for MMBS (or the so-called 'E blocks' in general)
 be needed, then please contact the linux-media mailing list: &v4l-ml;.</para>

   <section>
     <title>Querying Capabilities</title>

     <para>Devices supporting the RDS capturing API set
 the <constant>V4L2_CAP_RDS_CAPTURE</constant> flag in
 the <structfield>capabilities</structfield> field of &v4l2-capability;
 returned by the &VIDIOC-QUERYCAP; ioctl.  Any tuner that supports RDS
 will set the <constant>V4L2_TUNER_CAP_RDS</constant> flag in
 the <structfield>capability</structfield> field of &v4l2-tuner;.  If
 the driver only passes RDS blocks without interpreting the data
 the <constant>V4L2_TUNER_SUB_RDS_BLOCK_IO</constant> flag has to be
 set, see <link linkend="reading-rds-data">Reading RDS data</link>.
 For future use the
 flag <constant>V4L2_TUNER_SUB_RDS_CONTROLS</constant> has also been
 defined. However, a driver for a radio tuner with this capability does
 not yet exist, so if you are planning to write such a driver you
 should discuss this on the linux-media mailing list: &v4l-ml;.</para>

     <para> Whether an RDS signal is present can be detected by looking
 at the <structfield>rxsubchans</structfield> field of &v4l2-tuner;:
 the <constant>V4L2_TUNER_SUB_RDS</constant> will be set if RDS data
 was detected.</para>

     <para>Devices supporting the RDS output API
 set the <constant>V4L2_CAP_RDS_OUTPUT</constant> flag in
 the <structfield>capabilities</structfield> field of &v4l2-capability;
 returned by the &VIDIOC-QUERYCAP; ioctl.
 Any modulator that supports RDS will set the
 <constant>V4L2_TUNER_CAP_RDS</constant> flag in the <structfield>capability</structfield>
 field of &v4l2-modulator;.
 In order to enable the RDS transmission one must set the <constant>V4L2_TUNER_SUB_RDS</constant>
 bit in the <structfield>txsubchans</structfield> field of &v4l2-modulator;.
 If the driver only passes RDS blocks without interpreting the data
 the <constant>V4L2_TUNER_SUB_RDS_BLOCK_IO</constant> flag has to be set. If the
 tuner is capable of handling RDS entities like program identification codes and radio
 text, the flag <constant>V4L2_TUNER_SUB_RDS_CONTROLS</constant> should be set,
 see <link linkend="writing-rds-data">Writing RDS data</link> and
 <link linkend="fm-tx-controls">FM Transmitter Control Reference</link>.</para>
   </section>

   <section  id="reading-rds-data">
     <title>Reading RDS data</title>

       <para>RDS data can be read from the radio device
 with the &func-read; function. The data is packed in groups of three bytes.</para>
   </section>

   <section  id="writing-rds-data">
     <title>Writing RDS data</title>

       <para>RDS data can be written to the radio device
 with the &func-write; function. The data is packed in groups of three bytes,
 as follows:</para>
   </section>

   <section>
     <title>RDS datastructures</title>
     <table frame="none" pgwide="1" id="v4l2-rds-data">
       <title>struct
 <structname>v4l2_rds_data</structname></title>
       <tgroup cols="3">
 	<colspec colname="c1" colwidth="1*" />
 	<colspec colname="c2" colwidth="1*" />
 	<colspec colname="c3" colwidth="5*" />
 	<tbody valign="top">
 	  <row>
 	    <entry>__u8</entry>
 	    <entry><structfield>lsb</structfield></entry>
 	    <entry>Least Significant Byte of RDS Block</entry>
 	  </row>
 	  <row>
 	    <entry>__u8</entry>
 	    <entry><structfield>msb</structfield></entry>
 	    <entry>Most Significant Byte of RDS Block</entry>
 	  </row>
 	  <row>
 	    <entry>__u8</entry>
 	    <entry><structfield>block</structfield></entry>
 	    <entry>Block description</entry>
 	  </row>
 	</tbody>
       </tgroup>
     </table>
     <table frame="none" pgwide="1" id="v4l2-rds-block">
       <title>Block description</title>
       <tgroup cols="2">
 	<colspec colname="c1" colwidth="1*" />
 	<colspec colname="c2" colwidth="5*" />
 	<tbody valign="top">
 	  <row>
 	    <entry>Bits 0-2</entry>
 	    <entry>Block (aka offset) of the received data.</entry>
 	  </row>
 	  <row>
 	    <entry>Bits 3-5</entry>
 	    <entry>Deprecated. Currently identical to bits 0-2. Do not use these bits.</entry>
 	  </row>
 	  <row>
 	    <entry>Bit 6</entry>
 	    <entry>Corrected bit. Indicates that an error was corrected for this data block.</entry>
 	  </row>
 	  <row>
 	    <entry>Bit 7</entry>
 	    <entry>Error bit. Indicates that an uncorrectable error occurred during reception of this block.</entry>
 	  </row>
 	</tbody>
       </tgroup>
     </table>

     <table frame="none" pgwide="1" id="v4l2-rds-block-codes">
       <title>Block defines</title>
       <tgroup cols="4">
 	<colspec colname="c1" colwidth="1*" />
 	<colspec colname="c2" colwidth="1*" />
 	<colspec colname="c3" colwidth="1*" />
 	<colspec colname="c4" colwidth="5*" />
 	<tbody valign="top">
 	  <row>
 	    <entry>V4L2_RDS_BLOCK_MSK</entry>
 	    <entry> </entry>
 	    <entry>7</entry>
 	    <entry>Mask for bits 0-2 to get the block ID.</entry>
 	  </row>
 	  <row>
 	    <entry>V4L2_RDS_BLOCK_A</entry>
 	    <entry> </entry>
 	    <entry>0</entry>
 	    <entry>Block A.</entry>
 	  </row>
 	  <row>
 	    <entry>V4L2_RDS_BLOCK_B</entry>
 	    <entry> </entry>
 	    <entry>1</entry>
 	    <entry>Block B.</entry>
 	  </row>
 	  <row>
 	    <entry>V4L2_RDS_BLOCK_C</entry>
 	    <entry> </entry>
 	    <entry>2</entry>
 	    <entry>Block C.</entry>
 	  </row>
 	  <row>
 	    <entry>V4L2_RDS_BLOCK_D</entry>
 	    <entry> </entry>
 	    <entry>3</entry>
 	    <entry>Block D.</entry>
 	  </row>
 	  <row>
 	    <entry>V4L2_RDS_BLOCK_C_ALT</entry>
 	    <entry> </entry>
 	    <entry>4</entry>
 	    <entry>Block C'.</entry>
 	  </row>
 	  <row>
 	    <entry>V4L2_RDS_BLOCK_INVALID</entry>
 	    <entry>read-only</entry>
 	    <entry>7</entry>
 	    <entry>An invalid block.</entry>
 	  </row>
 	  <row>
 	    <entry>V4L2_RDS_BLOCK_CORRECTED</entry>
 	    <entry>read-only</entry>
 	    <entry>0x40</entry>
 	    <entry>A bit error was detected but corrected.</entry>
 	  </row>
 	  <row>
 	    <entry>V4L2_RDS_BLOCK_ERROR</entry>
 	    <entry>read-only</entry>
 	    <entry>0x80</entry>
 	    <entry>An uncorrectable error occurred.</entry>
 	  </row>
 	</tbody>
       </tgroup>
     </table>
   </section>

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	<title>RDS Interface</title>

	<para>The Radio Data System transmits supplementary
	information in binary format, for example the station name or travel
	information, on an inaudible audio subcarrier of a radio program. This
	interface is aimed at devices capable of receiving and/or transmitting RDS
	information.</para>

	<para>For more information see the core RDS standard <xref linkend="en50067" />
	and the RBDS standard <xref linkend="nrsc4" />.</para>

	<para>Note that the RBDS standard as is used in the USA is almost identical
	to the RDS standard. Any RDS decoder/encoder can also handle RBDS. Only some of the
	fields have slightly different meanings. See the RBDS standard for more
	information.</para>

	<para>The RBDS standard also specifies support for MMBS (Modified Mobile Search).
	This is a proprietary format which seems to be discontinued. The RDS interface does not
	support this format. Should support for MMBS (or the so-called 'E blocks' in general)
	be needed, then please contact the linux-media mailing list: &v4l-ml;.</para>

	<section>
	<title>Querying Capabilities</title>

	<para>Devices supporting the RDS capturing API set
	the <constant>V4L2_CAP_RDS_CAPTURE</constant> flag in
	the <structfield>capabilities</structfield> field of &v4l2-capability;
	returned by the &VIDIOC-QUERYCAP; ioctl. Any tuner that supports RDS
	will set the <constant>V4L2_TUNER_CAP_RDS</constant> flag in
	the <structfield>capability</structfield> field of &v4l2-tuner;. If
	the driver only passes RDS blocks without interpreting the data
	the <constant>V4L2_TUNER_SUB_RDS_BLOCK_IO</constant> flag has to be
	set, see <link linkend="reading-rds-data">Reading RDS data</link>.
	For future use the
	flag <constant>V4L2_TUNER_SUB_RDS_CONTROLS</constant> has also been
	defined. However, a driver for a radio tuner with this capability does
	not yet exist, so if you are planning to write such a driver you
	should discuss this on the linux-media mailing list: &v4l-ml;.</para>

	<para> Whether an RDS signal is present can be detected by looking
	at the <structfield>rxsubchans</structfield> field of &v4l2-tuner;:
	the <constant>V4L2_TUNER_SUB_RDS</constant> will be set if RDS data
	was detected.</para>

	<para>Devices supporting the RDS output API
	set the <constant>V4L2_CAP_RDS_OUTPUT</constant> flag in
	the <structfield>capabilities</structfield> field of &v4l2-capability;
	returned by the &VIDIOC-QUERYCAP; ioctl.
	Any modulator that supports RDS will set the
	<constant>V4L2_TUNER_CAP_RDS</constant> flag in the <structfield>capability</structfield>
	field of &v4l2-modulator;.
	In order to enable the RDS transmission one must set the <constant>V4L2_TUNER_SUB_RDS</constant>
	bit in the <structfield>txsubchans</structfield> field of &v4l2-modulator;.
	If the driver only passes RDS blocks without interpreting the data
	the <constant>V4L2_TUNER_SUB_RDS_BLOCK_IO</constant> flag has to be set. If the
	tuner is capable of handling RDS entities like program identification codes and radio
	text, the flag <constant>V4L2_TUNER_SUB_RDS_CONTROLS</constant> should be set,
	see <link linkend="writing-rds-data">Writing RDS data</link> and
	<link linkend="fm-tx-controls">FM Transmitter Control Reference</link>.</para>
	</section>

	<section id="reading-rds-data">
	<title>Reading RDS data</title>

	<para>RDS data can be read from the radio device
	with the &func-read; function. The data is packed in groups of three bytes.</para>
	</section>

	<section id="writing-rds-data">
	<title>Writing RDS data</title>

	<para>RDS data can be written to the radio device
	with the &func-write; function. The data is packed in groups of three bytes,
	as follows:</para>
	</section>

	<section>
	<title>RDS datastructures</title>
	<table frame="none" pgwide="1" id="v4l2-rds-data">
	<title>struct
	<structname>v4l2_rds_data</structname></title>
	<tgroup cols="3">
	<colspec colname="c1" colwidth="1*" />
	<colspec colname="c2" colwidth="1*" />
	<colspec colname="c3" colwidth="5*" />
	<tbody valign="top">
	<row>
	<entry>__u8</entry>
	<entry><structfield>lsb</structfield></entry>
	<entry>Least Significant Byte of RDS Block</entry>
	</row>
	<row>
	<entry>__u8</entry>
	<entry><structfield>msb</structfield></entry>
	<entry>Most Significant Byte of RDS Block</entry>
	</row>
	<row>
	<entry>__u8</entry>
	<entry><structfield>block</structfield></entry>
	<entry>Block description</entry>
	</row>
	</tbody>
	</tgroup>
	</table>
	<table frame="none" pgwide="1" id="v4l2-rds-block">
	<title>Block description</title>
	<tgroup cols="2">
	<colspec colname="c1" colwidth="1*" />
	<colspec colname="c2" colwidth="5*" />
	<tbody valign="top">
	<row>
	<entry>Bits 0-2</entry>
	<entry>Block (aka offset) of the received data.</entry>
	</row>
	<row>
	<entry>Bits 3-5</entry>
	<entry>Deprecated. Currently identical to bits 0-2. Do not use these bits.</entry>
	</row>
	<row>
	<entry>Bit 6</entry>
	<entry>Corrected bit. Indicates that an error was corrected for this data block.</entry>
	</row>
	<row>
	<entry>Bit 7</entry>
	<entry>Error bit. Indicates that an uncorrectable error occurred during reception of this block.</entry>
	</row>
	</tbody>
	</tgroup>
	</table>

	<table frame="none" pgwide="1" id="v4l2-rds-block-codes">
	<title>Block defines</title>
	<tgroup cols="4">
	<colspec colname="c1" colwidth="1*" />
	<colspec colname="c2" colwidth="1*" />
	<colspec colname="c3" colwidth="1*" />
	<colspec colname="c4" colwidth="5*" />
	<tbody valign="top">
	<row>
	<entry>V4L2_RDS_BLOCK_MSK</entry>
	<entry> </entry>
	<entry>7</entry>
	<entry>Mask for bits 0-2 to get the block ID.</entry>
	</row>
	<row>
	<entry>V4L2_RDS_BLOCK_A</entry>
	<entry> </entry>
	<entry>0</entry>
	<entry>Block A.</entry>
	</row>
	<row>
	<entry>V4L2_RDS_BLOCK_B</entry>
	<entry> </entry>
	<entry>1</entry>
	<entry>Block B.</entry>
	</row>
	<row>
	<entry>V4L2_RDS_BLOCK_C</entry>
	<entry> </entry>
	<entry>2</entry>
	<entry>Block C.</entry>
	</row>
	<row>
	<entry>V4L2_RDS_BLOCK_D</entry>
	<entry> </entry>
	<entry>3</entry>
	<entry>Block D.</entry>
	</row>
	<row>
	<entry>V4L2_RDS_BLOCK_C_ALT</entry>
	<entry> </entry>
	<entry>4</entry>
	<entry>Block C'.</entry>
	</row>
	<row>
	<entry>V4L2_RDS_BLOCK_INVALID</entry>
	<entry>read-only</entry>
	<entry>7</entry>
	<entry>An invalid block.</entry>
	</row>
	<row>
	<entry>V4L2_RDS_BLOCK_CORRECTED</entry>
	<entry>read-only</entry>
	<entry>0x40</entry>
	<entry>A bit error was detected but corrected.</entry>
	</row>
	<row>
	<entry>V4L2_RDS_BLOCK_ERROR</entry>
	<entry>read-only</entry>
	<entry>0x80</entry>
	<entry>An uncorrectable error occurred.</entry>
	</row>
	</tbody>
	</tgroup>
	</table>
	</section>

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