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8e080c2e MCC |
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 | |
eb8942e9 | 6 | interface is aimed at devices capable of receiving and/or transmitting RDS |
8e080c2e MCC |
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 | |
eb8942e9 MA |
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> | |
8e080c2e MCC |
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 | ||
eb8942e9 MA |
25 | <para>Devices supporting the RDS capturing API set |
26 | the <constant>V4L2_CAP_RDS_CAPTURE</constant> flag in | |
8e080c2e | 27 | the <structfield>capabilities</structfield> field of &v4l2-capability; |
eb8942e9 MA |
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 | |
146d35b0 | 32 | the <constant>V4L2_TUNER_CAP_RDS_BLOCK_IO</constant> flag has to be |
eb8942e9 MA |
33 | set, see <link linkend="reading-rds-data">Reading RDS data</link>. |
34 | For future use the | |
146d35b0 | 35 | flag <constant>V4L2_TUNER_CAP_RDS_CONTROLS</constant> has also been |
eb8942e9 MA |
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> | |
8e080c2e MCC |
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> | |
eb8942e9 MA |
53 | bit in the <structfield>txsubchans</structfield> field of &v4l2-modulator;. |
54 | If the driver only passes RDS blocks without interpreting the data | |
146d35b0 | 55 | the <constant>V4L2_TUNER_CAP_RDS_BLOCK_IO</constant> flag has to be set. If the |
eb8942e9 | 56 | tuner is capable of handling RDS entities like program identification codes and radio |
146d35b0 | 57 | text, the flag <constant>V4L2_TUNER_CAP_RDS_CONTROLS</constant> should be set, |
eb8942e9 MA |
58 | see <link linkend="writing-rds-data">Writing RDS data</link> and |
59 | <link linkend="fm-tx-controls">FM Transmitter Control Reference</link>.</para> | |
8e080c2e MCC |
60 | </section> |
61 | ||
eb8942e9 | 62 | <section id="reading-rds-data"> |
8e080c2e MCC |
63 | <title>Reading RDS data</title> |
64 | ||
65 | <para>RDS data can be read from the radio device | |
eb8942e9 MA |
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, | |
8e080c2e | 74 | as follows:</para> |
eb8942e9 MA |
75 | </section> |
76 | ||
77 | <section> | |
3a6be8d8 | 78 | <title>RDS datastructures</title> |
8e080c2e MCC |
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> | |
3a6be8d8 | 133 | <tgroup cols="4"> |
8e080c2e MCC |
134 | <colspec colname="c1" colwidth="1*" /> |
135 | <colspec colname="c2" colwidth="1*" /> | |
3a6be8d8 HV |
136 | <colspec colname="c3" colwidth="1*" /> |
137 | <colspec colname="c4" colwidth="5*" /> | |
8e080c2e MCC |
138 | <tbody valign="top"> |
139 | <row> | |
140 | <entry>V4L2_RDS_BLOCK_MSK</entry> | |
eb8942e9 | 141 | <entry> </entry> |
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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> | |
eb8942e9 | 147 | <entry> </entry> |
8e080c2e MCC |
148 | <entry>0</entry> |
149 | <entry>Block A.</entry> | |
150 | </row> | |
151 | <row> | |
152 | <entry>V4L2_RDS_BLOCK_B</entry> | |
eb8942e9 | 153 | <entry> </entry> |
8e080c2e MCC |
154 | <entry>1</entry> |
155 | <entry>Block B.</entry> | |
156 | </row> | |
157 | <row> | |
158 | <entry>V4L2_RDS_BLOCK_C</entry> | |
eb8942e9 | 159 | <entry> </entry> |
8e080c2e MCC |
160 | <entry>2</entry> |
161 | <entry>Block C.</entry> | |
162 | </row> | |
163 | <row> | |
164 | <entry>V4L2_RDS_BLOCK_D</entry> | |
eb8942e9 | 165 | <entry> </entry> |
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166 | <entry>3</entry> |
167 | <entry>Block D.</entry> | |
168 | </row> | |
169 | <row> | |
170 | <entry>V4L2_RDS_BLOCK_C_ALT</entry> | |
eb8942e9 | 171 | <entry> </entry> |
8e080c2e MCC |
172 | <entry>4</entry> |
173 | <entry>Block C'.</entry> | |
174 | </row> | |
175 | <row> | |
176 | <entry>V4L2_RDS_BLOCK_INVALID</entry> | |
eb8942e9 | 177 | <entry>read-only</entry> |
8e080c2e MCC |
178 | <entry>7</entry> |
179 | <entry>An invalid block.</entry> | |
180 | </row> | |
181 | <row> | |
182 | <entry>V4L2_RDS_BLOCK_CORRECTED</entry> | |
eb8942e9 | 183 | <entry>read-only</entry> |
8e080c2e MCC |
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> | |
eb8942e9 | 189 | <entry>read-only</entry> |
8e080c2e | 190 | <entry>0x80</entry> |
eb8942e9 | 191 | <entry>An uncorrectable error occurred.</entry> |
8e080c2e MCC |
192 | </row> |
193 | </tbody> | |
194 | </tgroup> | |
195 | </table> | |
196 | </section> |