Mauro Carvalho Chehab | 8e080c2 | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 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 decoding 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 can also handle RBDS. Only some of the fields |
| 14 | have slightly different meanings. See the RBDS standard for more information.</para> |
| 15 | |
| 16 | <para>The RBDS standard also specifies support for MMBS (Modified Mobile Search). |
| 17 | This is a proprietary format which seems to be discontinued. The RDS interface does not |
| 18 | support this format. Should support for MMBS (or the so-called 'E blocks' in general) |
| 19 | be needed, then please contact the linux-media mailing list: &v4l-ml;.</para> |
| 20 | |
| 21 | <section> |
| 22 | <title>Querying Capabilities</title> |
| 23 | |
| 24 | <para>Devices supporting the RDS capturing API |
| 25 | set the <constant>V4L2_CAP_RDS_CAPTURE</constant> flag in |
| 26 | the <structfield>capabilities</structfield> field of &v4l2-capability; |
| 27 | returned by the &VIDIOC-QUERYCAP; ioctl. |
| 28 | Any tuner that supports RDS will set the |
| 29 | <constant>V4L2_TUNER_CAP_RDS</constant> flag in the <structfield>capability</structfield> |
| 30 | field of &v4l2-tuner;. |
| 31 | Whether an RDS signal is present can be detected by looking at |
| 32 | the <structfield>rxsubchans</structfield> field of &v4l2-tuner;: the |
| 33 | <constant>V4L2_TUNER_SUB_RDS</constant> will be set if RDS data was detected.</para> |
| 34 | |
| 35 | <para>Devices supporting the RDS output API |
| 36 | set the <constant>V4L2_CAP_RDS_OUTPUT</constant> flag in |
| 37 | the <structfield>capabilities</structfield> field of &v4l2-capability; |
| 38 | returned by the &VIDIOC-QUERYCAP; ioctl. |
| 39 | Any modulator that supports RDS will set the |
| 40 | <constant>V4L2_TUNER_CAP_RDS</constant> flag in the <structfield>capability</structfield> |
| 41 | field of &v4l2-modulator;. |
| 42 | In order to enable the RDS transmission one must set the <constant>V4L2_TUNER_SUB_RDS</constant> |
| 43 | bit in the <structfield>txsubchans</structfield> field of &v4l2-modulator;.</para> |
| 44 | |
| 45 | </section> |
| 46 | |
| 47 | <section> |
| 48 | <title>Reading RDS data</title> |
| 49 | |
| 50 | <para>RDS data can be read from the radio device |
| 51 | with the &func-read; function. The data is packed in groups of three bytes, |
| 52 | as follows:</para> |
| 53 | <table frame="none" pgwide="1" id="v4l2-rds-data"> |
| 54 | <title>struct |
| 55 | <structname>v4l2_rds_data</structname></title> |
| 56 | <tgroup cols="3"> |
| 57 | <colspec colname="c1" colwidth="1*" /> |
| 58 | <colspec colname="c2" colwidth="1*" /> |
| 59 | <colspec colname="c3" colwidth="5*" /> |
| 60 | <tbody valign="top"> |
| 61 | <row> |
| 62 | <entry>__u8</entry> |
| 63 | <entry><structfield>lsb</structfield></entry> |
| 64 | <entry>Least Significant Byte of RDS Block</entry> |
| 65 | </row> |
| 66 | <row> |
| 67 | <entry>__u8</entry> |
| 68 | <entry><structfield>msb</structfield></entry> |
| 69 | <entry>Most Significant Byte of RDS Block</entry> |
| 70 | </row> |
| 71 | <row> |
| 72 | <entry>__u8</entry> |
| 73 | <entry><structfield>block</structfield></entry> |
| 74 | <entry>Block description</entry> |
| 75 | </row> |
| 76 | </tbody> |
| 77 | </tgroup> |
| 78 | </table> |
| 79 | <table frame="none" pgwide="1" id="v4l2-rds-block"> |
| 80 | <title>Block description</title> |
| 81 | <tgroup cols="2"> |
| 82 | <colspec colname="c1" colwidth="1*" /> |
| 83 | <colspec colname="c2" colwidth="5*" /> |
| 84 | <tbody valign="top"> |
| 85 | <row> |
| 86 | <entry>Bits 0-2</entry> |
| 87 | <entry>Block (aka offset) of the received data.</entry> |
| 88 | </row> |
| 89 | <row> |
| 90 | <entry>Bits 3-5</entry> |
| 91 | <entry>Deprecated. Currently identical to bits 0-2. Do not use these bits.</entry> |
| 92 | </row> |
| 93 | <row> |
| 94 | <entry>Bit 6</entry> |
| 95 | <entry>Corrected bit. Indicates that an error was corrected for this data block.</entry> |
| 96 | </row> |
| 97 | <row> |
| 98 | <entry>Bit 7</entry> |
| 99 | <entry>Error bit. Indicates that an uncorrectable error occurred during reception of this block.</entry> |
| 100 | </row> |
| 101 | </tbody> |
| 102 | </tgroup> |
| 103 | </table> |
| 104 | |
| 105 | <table frame="none" pgwide="1" id="v4l2-rds-block-codes"> |
| 106 | <title>Block defines</title> |
| 107 | <tgroup cols="3"> |
| 108 | <colspec colname="c1" colwidth="1*" /> |
| 109 | <colspec colname="c2" colwidth="1*" /> |
| 110 | <colspec colname="c3" colwidth="5*" /> |
| 111 | <tbody valign="top"> |
| 112 | <row> |
| 113 | <entry>V4L2_RDS_BLOCK_MSK</entry> |
| 114 | <entry>7</entry> |
| 115 | <entry>Mask for bits 0-2 to get the block ID.</entry> |
| 116 | </row> |
| 117 | <row> |
| 118 | <entry>V4L2_RDS_BLOCK_A</entry> |
| 119 | <entry>0</entry> |
| 120 | <entry>Block A.</entry> |
| 121 | </row> |
| 122 | <row> |
| 123 | <entry>V4L2_RDS_BLOCK_B</entry> |
| 124 | <entry>1</entry> |
| 125 | <entry>Block B.</entry> |
| 126 | </row> |
| 127 | <row> |
| 128 | <entry>V4L2_RDS_BLOCK_C</entry> |
| 129 | <entry>2</entry> |
| 130 | <entry>Block C.</entry> |
| 131 | </row> |
| 132 | <row> |
| 133 | <entry>V4L2_RDS_BLOCK_D</entry> |
| 134 | <entry>3</entry> |
| 135 | <entry>Block D.</entry> |
| 136 | </row> |
| 137 | <row> |
| 138 | <entry>V4L2_RDS_BLOCK_C_ALT</entry> |
| 139 | <entry>4</entry> |
| 140 | <entry>Block C'.</entry> |
| 141 | </row> |
| 142 | <row> |
| 143 | <entry>V4L2_RDS_BLOCK_INVALID</entry> |
| 144 | <entry>7</entry> |
| 145 | <entry>An invalid block.</entry> |
| 146 | </row> |
| 147 | <row> |
| 148 | <entry>V4L2_RDS_BLOCK_CORRECTED</entry> |
| 149 | <entry>0x40</entry> |
| 150 | <entry>A bit error was detected but corrected.</entry> |
| 151 | </row> |
| 152 | <row> |
| 153 | <entry>V4L2_RDS_BLOCK_ERROR</entry> |
| 154 | <entry>0x80</entry> |
| 155 | <entry>An incorrectable error occurred.</entry> |
| 156 | </row> |
| 157 | </tbody> |
| 158 | </tgroup> |
| 159 | </table> |
| 160 | </section> |
| 161 | |
| 162 | <!-- |
| 163 | Local Variables: |
| 164 | mode: sgml |
| 165 | sgml-parent-document: "v4l2.sgml" |
| 166 | indent-tabs-mode: nil |
| 167 | End: |
| 168 | --> |