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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_CAP_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_CAP_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_CAP_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_CAP_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>