| <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> |
| |
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