<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 decoding RDS
+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 can also handle RBDS. Only some of the fields
-have slightly different meanings. See the RBDS standard for more information.</para>
+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
<section>
<title>Querying Capabilities</title>
- <para>Devices supporting the RDS capturing API
-set the <constant>V4L2_CAP_RDS_CAPTURE</constant> flag in
+ <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;.
-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>
+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
<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;.</para>
-
+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>
+ <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,
+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>
<table frame="none" pgwide="1" id="v4l2-rds-data">
<title>struct
<structname>v4l2_rds_data</structname></title>
<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 incorrectable error occurred.</entry>
+ <entry>An uncorrectable error occurred.</entry>
</row>
</tbody>
</tgroup>
<para>Start a hardware frequency seek from the current frequency.
To do this applications initialize the <structfield>tuner</structfield>,
-<structfield>type</structfield>, <structfield>seek_upward</structfield> and
+<structfield>type</structfield>, <structfield>seek_upward</structfield>,
+<structfield>spacing</structfield> and
<structfield>wrap_around</structfield> fields, and zero out the
<structfield>reserved</structfield> array of a &v4l2-hw-freq-seek; and
call the <constant>VIDIOC_S_HW_FREQ_SEEK</constant> ioctl with a pointer
</row>
<row>
<entry>__u32</entry>
- <entry><structfield>reserved</structfield>[8]</entry>
+ <entry><structfield>spacing</structfield></entry>
+ <entry>If non-zero, defines the hardware seek resolution in Hz. The driver selects the nearest value that is supported by the device. If spacing is zero a reasonable default value is used.</entry>
+ </row>
+ <row>
+ <entry>__u32</entry>
+ <entry><structfield>reserved</structfield>[7]</entry>
<entry>Reserved for future extensions. Drivers and
applications must set the array to zero.</entry>
</row>
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