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diff --git a/Documentation/DocBook/media/v4l/dev-rds.xml b/Documentation/DocBook/media/v4l/dev-rds.xml new file mode 100644 index 00000000..38883a41 --- /dev/null +++ b/Documentation/DocBook/media/v4l/dev-rds.xml @@ -0,0 +1,196 @@ + <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> |