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Based on kernel version 3.13. Page generated on 2014-01-20 22:02 EST.

1	     <title>RDS Interface</title>
2	
3	      <para>The Radio Data System transmits supplementary
4	information in binary format, for example the station name or travel
5	information, on an inaudible audio subcarrier of a radio program. This
6	interface is aimed at devices capable of receiving and/or transmitting RDS
7	information.</para>
8	
9	      <para>For more information see the core RDS standard <xref linkend="iec62106" />
10	and the RBDS standard <xref linkend="nrsc4" />.</para>
11	
12	      <para>Note that the RBDS standard as is used in the USA is almost identical
13	to the RDS standard. Any RDS decoder/encoder can also handle RBDS. Only some of the
14	fields have slightly different meanings. See the RBDS standard for more
15	information.</para>
16	
17	      <para>The RBDS standard also specifies support for MMBS (Modified Mobile Search).
18	This is a proprietary format which seems to be discontinued. The RDS interface does not
19	support this format. Should support for MMBS (or the so-called 'E blocks' in general)
20	be 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
26	the <constant>V4L2_CAP_RDS_CAPTURE</constant> flag in
27	the <structfield>capabilities</structfield> field of &v4l2-capability;
28	returned by the &VIDIOC-QUERYCAP; ioctl.  Any tuner that supports RDS
29	will set the <constant>V4L2_TUNER_CAP_RDS</constant> flag in
30	the <structfield>capability</structfield> field of &v4l2-tuner;.  If
31	the driver only passes RDS blocks without interpreting the data
32	the <constant>V4L2_TUNER_CAP_RDS_BLOCK_IO</constant> flag has to be
33	set, see <link linkend="reading-rds-data">Reading RDS data</link>.
34	For future use the
35	flag <constant>V4L2_TUNER_CAP_RDS_CONTROLS</constant> has also been
36	defined. However, a driver for a radio tuner with this capability does
37	not yet exist, so if you are planning to write such a driver you
38	should 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
41	at the <structfield>rxsubchans</structfield> field of &v4l2-tuner;:
42	the <constant>V4L2_TUNER_SUB_RDS</constant> will be set if RDS data
43	was detected.</para>
44	
45	    <para>Devices supporting the RDS output API
46	set the <constant>V4L2_CAP_RDS_OUTPUT</constant> flag in
47	the <structfield>capabilities</structfield> field of &v4l2-capability;
48	returned by the &VIDIOC-QUERYCAP; ioctl.
49	Any modulator that supports RDS will set the
50	<constant>V4L2_TUNER_CAP_RDS</constant> flag in the <structfield>capability</structfield>
51	field of &v4l2-modulator;.
52	In order to enable the RDS transmission one must set the <constant>V4L2_TUNER_SUB_RDS</constant>
53	bit in the <structfield>txsubchans</structfield> field of &v4l2-modulator;.
54	If the driver only passes RDS blocks without interpreting the data
55	the <constant>V4L2_TUNER_CAP_RDS_BLOCK_IO</constant> flag has to be set. If the
56	tuner is capable of handling RDS entities like program identification codes and radio
57	text, the flag <constant>V4L2_TUNER_CAP_RDS_CONTROLS</constant> should be set,
58	see <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
66	with 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
73	with the &func-write; function. The data is packed in groups of three bytes,
74	as 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>
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