1     <title>RDS Interface</title>
2
3      <para>The Radio Data System transmits supplementary
4information in binary format, for example the station name or travel
5information, on an inaudible audio subcarrier of a radio program. This
6interface is aimed at devices capable of receiving and/or transmitting RDS
7information.</para>
8
9      <para>For more information see the core RDS standard <xref linkend="iec62106" />
10and the RBDS standard <xref linkend="nrsc4" />.</para>
11
12      <para>Note that the RBDS standard as is used in the USA is almost identical
13to the RDS standard. Any RDS decoder/encoder can also handle RBDS. Only some of the
14fields have slightly different meanings. See the RBDS standard for more
15information.</para>
16
17      <para>The RBDS standard also specifies support for MMBS (Modified Mobile Search).
18This is a proprietary format which seems to be discontinued. The RDS interface does not
19support this format. Should support for MMBS (or the so-called 'E blocks' in general)
20be needed, then please contact the linux-media mailing list: &v4l-ml;.</para>
21
22  <section>
23    <title>Querying Capabilities</title>
24
25    <para>Devices supporting the RDS capturing API set
26the <constant>V4L2_CAP_RDS_CAPTURE</constant> flag in
27the <structfield>capabilities</structfield> field of &v4l2-capability;
28returned by the &VIDIOC-QUERYCAP; ioctl.  Any tuner that supports RDS
29will set the <constant>V4L2_TUNER_CAP_RDS</constant> flag in
30the <structfield>capability</structfield> field of &v4l2-tuner;.  If
31the driver only passes RDS blocks without interpreting the data
32the <constant>V4L2_TUNER_CAP_RDS_BLOCK_IO</constant> flag has to be
33set, see <link linkend="reading-rds-data">Reading RDS data</link>.
34For future use the
35flag <constant>V4L2_TUNER_CAP_RDS_CONTROLS</constant> has also been
36defined. However, a driver for a radio tuner with this capability does
37not yet exist, so if you are planning to write such a driver you
38should discuss this on the linux-media mailing list: &v4l-ml;.</para>
39
40    <para> Whether an RDS signal is present can be detected by looking
41at the <structfield>rxsubchans</structfield> field of &v4l2-tuner;:
42the <constant>V4L2_TUNER_SUB_RDS</constant> will be set if RDS data
43was detected.</para>
44
45    <para>Devices supporting the RDS output API
46set the <constant>V4L2_CAP_RDS_OUTPUT</constant> flag in
47the <structfield>capabilities</structfield> field of &v4l2-capability;
48returned by the &VIDIOC-QUERYCAP; ioctl.
49Any modulator that supports RDS will set the
50<constant>V4L2_TUNER_CAP_RDS</constant> flag in the <structfield>capability</structfield>
51field of &v4l2-modulator;.
52In order to enable the RDS transmission one must set the <constant>V4L2_TUNER_SUB_RDS</constant>
53bit in the <structfield>txsubchans</structfield> field of &v4l2-modulator;.
54If the driver only passes RDS blocks without interpreting the data
55the <constant>V4L2_TUNER_CAP_RDS_BLOCK_IO</constant> flag has to be set. If the
56tuner is capable of handling RDS entities like program identification codes and radio
57text, the flag <constant>V4L2_TUNER_CAP_RDS_CONTROLS</constant> should be set,
58see <link linkend="writing-rds-data">Writing RDS data</link> and
59<link linkend="fm-tx-controls">FM Transmitter Control Reference</link>.</para>
60  </section>
61
62  <section  id="reading-rds-data">
63    <title>Reading RDS data</title>
64
65      <para>RDS data can be read from the radio device
66with the &func-read; function. The data is packed in groups of three bytes.</para>
67  </section>
68
69  <section  id="writing-rds-data">
70    <title>Writing RDS data</title>
71
72      <para>RDS data can be written to the radio device
73with the &func-write; function. The data is packed in groups of three bytes,
74as follows:</para>
75  </section>
76
77  <section>
78    <title>RDS datastructures</title>
79    <table frame="none" pgwide="1" id="v4l2-rds-data">
80      <title>struct
81<structname>v4l2_rds_data</structname></title>
82      <tgroup cols="3">
83	<colspec colname="c1" colwidth="1*" />
84	<colspec colname="c2" colwidth="1*" />
85	<colspec colname="c3" colwidth="5*" />
86	<tbody valign="top">
87	  <row>
88	    <entry>__u8</entry>
89	    <entry><structfield>lsb</structfield></entry>
90	    <entry>Least Significant Byte of RDS Block</entry>
91	  </row>
92	  <row>
93	    <entry>__u8</entry>
94	    <entry><structfield>msb</structfield></entry>
95	    <entry>Most Significant Byte of RDS Block</entry>
96	  </row>
97	  <row>
98	    <entry>__u8</entry>
99	    <entry><structfield>block</structfield></entry>
100	    <entry>Block description</entry>
101	  </row>
102	</tbody>
103      </tgroup>
104    </table>
105    <table frame="none" pgwide="1" id="v4l2-rds-block">
106      <title>Block description</title>
107      <tgroup cols="2">
108	<colspec colname="c1" colwidth="1*" />
109	<colspec colname="c2" colwidth="5*" />
110	<tbody valign="top">
111	  <row>
112	    <entry>Bits 0-2</entry>
113	    <entry>Block (aka offset) of the received data.</entry>
114	  </row>
115	  <row>
116	    <entry>Bits 3-5</entry>
117	    <entry>Deprecated. Currently identical to bits 0-2. Do not use these bits.</entry>
118	  </row>
119	  <row>
120	    <entry>Bit 6</entry>
121	    <entry>Corrected bit. Indicates that an error was corrected for this data block.</entry>
122	  </row>
123	  <row>
124	    <entry>Bit 7</entry>
125	    <entry>Error bit. Indicates that an uncorrectable error occurred during reception of this block.</entry>
126	  </row>
127	</tbody>
128      </tgroup>
129    </table>
130
131    <table frame="none" pgwide="1" id="v4l2-rds-block-codes">
132      <title>Block defines</title>
133      <tgroup cols="4">
134	<colspec colname="c1" colwidth="1*" />
135	<colspec colname="c2" colwidth="1*" />
136	<colspec colname="c3" colwidth="1*" />
137	<colspec colname="c4" colwidth="5*" />
138	<tbody valign="top">
139	  <row>
140	    <entry>V4L2_RDS_BLOCK_MSK</entry>
141	    <entry> </entry>
142	    <entry>7</entry>
143	    <entry>Mask for bits 0-2 to get the block ID.</entry>
144	  </row>
145	  <row>
146	    <entry>V4L2_RDS_BLOCK_A</entry>
147	    <entry> </entry>
148	    <entry>0</entry>
149	    <entry>Block A.</entry>
150	  </row>
151	  <row>
152	    <entry>V4L2_RDS_BLOCK_B</entry>
153	    <entry> </entry>
154	    <entry>1</entry>
155	    <entry>Block B.</entry>
156	  </row>
157	  <row>
158	    <entry>V4L2_RDS_BLOCK_C</entry>
159	    <entry> </entry>
160	    <entry>2</entry>
161	    <entry>Block C.</entry>
162	  </row>
163	  <row>
164	    <entry>V4L2_RDS_BLOCK_D</entry>
165	    <entry> </entry>
166	    <entry>3</entry>
167	    <entry>Block D.</entry>
168	  </row>
169	  <row>
170	    <entry>V4L2_RDS_BLOCK_C_ALT</entry>
171	    <entry> </entry>
172	    <entry>4</entry>
173	    <entry>Block C'.</entry>
174	  </row>
175	  <row>
176	    <entry>V4L2_RDS_BLOCK_INVALID</entry>
177	    <entry>read-only</entry>
178	    <entry>7</entry>
179	    <entry>An invalid block.</entry>
180	  </row>
181	  <row>
182	    <entry>V4L2_RDS_BLOCK_CORRECTED</entry>
183	    <entry>read-only</entry>
184	    <entry>0x40</entry>
185	    <entry>A bit error was detected but corrected.</entry>
186	  </row>
187	  <row>
188	    <entry>V4L2_RDS_BLOCK_ERROR</entry>
189	    <entry>read-only</entry>
190	    <entry>0x80</entry>
191	    <entry>An uncorrectable error occurred.</entry>
192	  </row>
193	</tbody>
194      </tgroup>
195    </table>
196  </section>
197