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diff --git a/Documentation/userspace-api/media/v4l/dev-rds.rst b/Documentation/userspace-api/media/v4l/dev-rds.rst new file mode 100644 index 000000000..b1dadc245 --- /dev/null +++ b/Documentation/userspace-api/media/v4l/dev-rds.rst @@ -0,0 +1,176 @@ +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later +.. c:namespace:: V4L + +.. _rds: + +************* +RDS Interface +************* + +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/or transmitting RDS information. + +For more information see the core RDS standard :ref:`iec62106` and the +RBDS standard :ref:`nrsc4`. + +.. note:: + + Note that the RBDS standard as is used in the USA is almost + identical to the RDS standard. Any RDS decoder/encoder 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 <https://linuxtv.org/lists.php>`__. + +Querying Capabilities +===================== + +Devices supporting the RDS capturing API set the +``V4L2_CAP_RDS_CAPTURE`` flag in the ``capabilities`` field of struct +:c:type:`v4l2_capability` returned by the +:ref:`VIDIOC_QUERYCAP` ioctl. Any tuner that +supports RDS will set the ``V4L2_TUNER_CAP_RDS`` flag in the +``capability`` field of struct :c:type:`v4l2_tuner`. If the +driver only passes RDS blocks without interpreting the data the +``V4L2_TUNER_CAP_RDS_BLOCK_IO`` flag has to be set, see +:ref:`Reading RDS data <reading-rds-data>`. For future use the flag +``V4L2_TUNER_CAP_RDS_CONTROLS`` has also been defined. However, a driver +for a radio tuner with this capability does not yet exist, so if you are +planning to write such a driver you should discuss this on the +linux-media mailing list: +`https://linuxtv.org/lists.php <https://linuxtv.org/lists.php>`__. + +Whether an RDS signal is present can be detected by looking at the +``rxsubchans`` field of struct :c:type:`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 +:c:type:`v4l2_capability` returned by the +:ref:`VIDIOC_QUERYCAP` ioctl. Any modulator that +supports RDS will set the ``V4L2_TUNER_CAP_RDS`` flag in the +``capability`` field of struct +:c:type:`v4l2_modulator`. In order to enable the RDS +transmission one must set the ``V4L2_TUNER_SUB_RDS`` bit in the +``txsubchans`` field of struct +:c:type:`v4l2_modulator`. If the driver only passes RDS +blocks without interpreting the data the ``V4L2_TUNER_CAP_RDS_BLOCK_IO`` +flag has to be set. If the tuner is capable of handling RDS entities +like program identification codes and radio text, the flag +``V4L2_TUNER_CAP_RDS_CONTROLS`` should be set, see +:ref:`Writing RDS data <writing-rds-data>` and +:ref:`FM Transmitter Control Reference <fm-tx-controls>`. + +.. _reading-rds-data: + +Reading RDS data +================ + +RDS data can be read from the radio device with the +:c:func:`read()` function. The data is packed in groups of +three bytes. + +.. _writing-rds-data: + +Writing RDS data +================ + +RDS data can be written to the radio device with the +:c:func:`write()` function. The data is packed in groups of +three bytes, as follows: + +RDS datastructures +================== + +.. c:type:: v4l2_rds_data + +.. flat-table:: struct v4l2_rds_data + :header-rows: 0 + :stub-columns: 0 + :widths: 1 1 5 + + * - __u8 + - ``lsb`` + - Least Significant Byte of RDS Block + * - __u8 + - ``msb`` + - Most Significant Byte of RDS Block + * - __u8 + - ``block`` + - Block description + + +.. _v4l2-rds-block: + +.. tabularcolumns:: |p{2.9cm}|p{14.6cm}| + +.. flat-table:: Block description + :header-rows: 0 + :stub-columns: 0 + :widths: 1 5 + + * - 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. + + +.. _v4l2-rds-block-codes: + +.. tabularcolumns:: |p{6.4cm}|p{2.0cm}|p{1.2cm}|p{7.0cm}| + +.. flat-table:: Block defines + :header-rows: 0 + :stub-columns: 0 + :widths: 1 1 1 5 + + * - 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 + - read-only + - 7 + - An invalid block. + * - V4L2_RDS_BLOCK_CORRECTED + - read-only + - 0x40 + - A bit error was detected but corrected. + * - V4L2_RDS_BLOCK_ERROR + - read-only + - 0x80 + - An uncorrectable error occurred. |