Merge branch 'for-3.3/drivers' of git://git.kernel.dk/linux-block
[linux-2.6.git] / Documentation / DocBook / media / v4l / dev-rds.xml
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="en50067" />
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_SUB_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_SUB_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_SUB_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_SUB_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>
197
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