177 lines
5.1 KiB
ReStructuredText
177 lines
5.1 KiB
ReStructuredText
.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
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.. c:namespace:: V4L
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.. _rds:
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*************
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RDS Interface
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*************
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The Radio Data System transmits supplementary information in binary
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format, for example the station name or travel information, on an
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inaudible audio subcarrier of a radio program. This interface is aimed
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at devices capable of receiving and/or transmitting RDS information.
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For more information see the core RDS standard :ref:`iec62106` and the
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RBDS standard :ref:`nrsc4`.
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.. note::
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Note that the RBDS standard as is used in the USA is almost
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identical to the RDS standard. Any RDS decoder/encoder can also handle
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RBDS. Only some of the fields have slightly different meanings. See the
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RBDS standard for more information.
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The RBDS standard also specifies support for MMBS (Modified Mobile
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Search). This is a proprietary format which seems to be discontinued.
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The RDS interface does not support this format. Should support for MMBS
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(or the so-called 'E blocks' in general) be needed, then please contact
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the linux-media mailing list:
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`https://linuxtv.org/lists.php <https://linuxtv.org/lists.php>`__.
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Querying Capabilities
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=====================
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Devices supporting the RDS capturing API set the
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``V4L2_CAP_RDS_CAPTURE`` flag in the ``capabilities`` field of struct
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:c:type:`v4l2_capability` returned by the
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:ref:`VIDIOC_QUERYCAP` ioctl. Any tuner that
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supports RDS will set the ``V4L2_TUNER_CAP_RDS`` flag in the
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``capability`` field of struct :c:type:`v4l2_tuner`. If the
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driver only passes RDS blocks without interpreting the data the
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``V4L2_TUNER_CAP_RDS_BLOCK_IO`` flag has to be set, see
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:ref:`Reading RDS data <reading-rds-data>`. For future use the flag
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``V4L2_TUNER_CAP_RDS_CONTROLS`` has also been defined. However, a driver
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for a radio tuner with this capability does not yet exist, so if you are
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planning to write such a driver you should discuss this on the
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linux-media mailing list:
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`https://linuxtv.org/lists.php <https://linuxtv.org/lists.php>`__.
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Whether an RDS signal is present can be detected by looking at the
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``rxsubchans`` field of struct :c:type:`v4l2_tuner`: the
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``V4L2_TUNER_SUB_RDS`` will be set if RDS data was detected.
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Devices supporting the RDS output API set the ``V4L2_CAP_RDS_OUTPUT``
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flag in the ``capabilities`` field of struct
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:c:type:`v4l2_capability` returned by the
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:ref:`VIDIOC_QUERYCAP` ioctl. Any modulator that
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supports RDS will set the ``V4L2_TUNER_CAP_RDS`` flag in the
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``capability`` field of struct
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:c:type:`v4l2_modulator`. In order to enable the RDS
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transmission one must set the ``V4L2_TUNER_SUB_RDS`` bit in the
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``txsubchans`` field of struct
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:c:type:`v4l2_modulator`. If the driver only passes RDS
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blocks without interpreting the data the ``V4L2_TUNER_CAP_RDS_BLOCK_IO``
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flag has to be set. If the tuner is capable of handling RDS entities
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like program identification codes and radio text, the flag
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``V4L2_TUNER_CAP_RDS_CONTROLS`` should be set, see
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:ref:`Writing RDS data <writing-rds-data>` and
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:ref:`FM Transmitter Control Reference <fm-tx-controls>`.
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.. _reading-rds-data:
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Reading RDS data
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================
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RDS data can be read from the radio device with the
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:c:func:`read()` function. The data is packed in groups of
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three bytes.
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.. _writing-rds-data:
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Writing RDS data
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================
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RDS data can be written to the radio device with the
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:c:func:`write()` function. The data is packed in groups of
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three bytes, as follows:
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RDS datastructures
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==================
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.. c:type:: v4l2_rds_data
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.. flat-table:: struct v4l2_rds_data
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 1 5
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* - __u8
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- ``lsb``
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- Least Significant Byte of RDS Block
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* - __u8
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- ``msb``
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- Most Significant Byte of RDS Block
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* - __u8
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- ``block``
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- Block description
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.. _v4l2-rds-block:
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.. tabularcolumns:: |p{2.9cm}|p{14.6cm}|
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.. flat-table:: Block description
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 5
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* - Bits 0-2
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- Block (aka offset) of the received data.
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* - Bits 3-5
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- Deprecated. Currently identical to bits 0-2. Do not use these
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bits.
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* - Bit 6
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- Corrected bit. Indicates that an error was corrected for this data
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block.
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* - Bit 7
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- Error bit. Indicates that an uncorrectable error occurred during
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reception of this block.
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.. _v4l2-rds-block-codes:
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.. tabularcolumns:: |p{6.4cm}|p{2.0cm}|p{1.2cm}|p{7.0cm}|
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.. flat-table:: Block defines
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 1 1 5
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* - V4L2_RDS_BLOCK_MSK
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-
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- 7
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- Mask for bits 0-2 to get the block ID.
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* - V4L2_RDS_BLOCK_A
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-
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- 0
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- Block A.
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* - V4L2_RDS_BLOCK_B
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-
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- 1
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- Block B.
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* - V4L2_RDS_BLOCK_C
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-
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- 2
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- Block C.
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* - V4L2_RDS_BLOCK_D
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-
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- 3
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- Block D.
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* - V4L2_RDS_BLOCK_C_ALT
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-
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- 4
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- Block C'.
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* - V4L2_RDS_BLOCK_INVALID
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- read-only
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- 7
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- An invalid block.
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* - V4L2_RDS_BLOCK_CORRECTED
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- read-only
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- 0x40
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- A bit error was detected but corrected.
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* - V4L2_RDS_BLOCK_ERROR
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- read-only
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- 0x80
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- An uncorrectable error occurred.
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