Based on kernel version 4.7.2. Page generated on 2016-08-22 22:45 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>
