The Radio Data System transmits supplementary information in binary format, for example the station name or travel information, on an inaudible audio subcarrier of a radio program. This interface is aimed at devices capable of receiving and decoding RDS information.
For more information see the core RDS standard [EN 50067] and the RBDS standard [NRSC-4].
Note that the RBDS standard as is used in the USA is almost identical to the RDS standard. Any RDS decoder can also handle RBDS. Only some of the fields have slightly different meanings. See the RBDS standard for more information.
The RBDS standard also specifies support for MMBS (Modified Mobile Search). This is a proprietary format which seems to be discontinued. The RDS interface does not support this format. Should support for MMBS (or the so-called 'E blocks' in general) be needed, then please contact the linux-media mailing list: https://linuxtv.org/lists.php.
Devices supporting the RDS capturing API
set the V4L2_CAP_RDS_CAPTURE flag in
the capabilities field of struct v4l2_capability
returned by the VIDIOC_QUERYCAP ioctl.
Any tuner that supports RDS will set the
V4L2_TUNER_CAP_RDS flag in the capability
field of struct v4l2_tuner.
Whether an RDS signal is present can be detected by looking at
the rxsubchans field of struct v4l2_tuner: the
V4L2_TUNER_SUB_RDS will be set if RDS data was detected.
Devices supporting the RDS output API
set the V4L2_CAP_RDS_OUTPUT flag in
the capabilities field of struct v4l2_capability
returned by the VIDIOC_QUERYCAP ioctl.
Any modulator that supports RDS will set the
V4L2_TUNER_CAP_RDS flag in the capability
field of struct v4l2_modulator.
In order to enable the RDS transmission one must set the V4L2_TUNER_SUB_RDS
bit in the txsubchans field of struct v4l2_modulator.
RDS data can be read from the radio device
with the read() function. The data is packed in groups of three bytes,
as follows:
Table 4.15. struct v4l2_rds_data
| __u8 | lsb | Least Significant Byte of RDS Block |
| __u8 | msb | Most Significant Byte of RDS Block |
| __u8 | block | Block description |
Table 4.16. Block description
| Bits 0-2 | Block (aka offset) of the received data. |
| Bits 3-5 | Deprecated. Currently identical to bits 0-2. Do not use these bits. |
| Bit 6 | Corrected bit. Indicates that an error was corrected for this data block. |
| Bit 7 | Error bit. Indicates that an uncorrectable error occurred during reception of this block. |
Table 4.17. Block defines
| V4L2_RDS_BLOCK_MSK | 7 | Mask for bits 0-2 to get the block ID. |
| V4L2_RDS_BLOCK_A | 0 | Block A. |
| V4L2_RDS_BLOCK_B | 1 | Block B. |
| V4L2_RDS_BLOCK_C | 2 | Block C. |
| V4L2_RDS_BLOCK_D | 3 | Block D. |
| V4L2_RDS_BLOCK_C_ALT | 4 | Block C'. |
| V4L2_RDS_BLOCK_INVALID | 7 | An invalid block. |
| V4L2_RDS_BLOCK_CORRECTED | 0x40 | A bit error was detected but corrected. |
| V4L2_RDS_BLOCK_ERROR | 0x80 | An incorrectable error occurred. |