182 lines
7.1 KiB
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182 lines
7.1 KiB
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.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
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.. _fm-tx-controls:
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********************************
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FM Transmitter Control Reference
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********************************
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The FM Transmitter (FM_TX) class includes controls for common features
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of FM transmissions capable devices. Currently this class includes
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parameters for audio compression, pilot tone generation, audio deviation
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limiter, RDS transmission and tuning power features.
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.. _fm-tx-control-id:
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FM_TX Control IDs
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=================
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``V4L2_CID_FM_TX_CLASS (class)``
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The FM_TX class descriptor. Calling
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:ref:`VIDIOC_QUERYCTRL` for this control will
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return a description of this control class.
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``V4L2_CID_RDS_TX_DEVIATION (integer)``
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Configures RDS signal frequency deviation level in Hz. The range and
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step are driver-specific.
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``V4L2_CID_RDS_TX_PI (integer)``
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Sets the RDS Programme Identification field for transmission.
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``V4L2_CID_RDS_TX_PTY (integer)``
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Sets the RDS Programme Type field for transmission. This encodes up
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to 31 pre-defined programme types.
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``V4L2_CID_RDS_TX_PS_NAME (string)``
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Sets the Programme Service name (PS_NAME) for transmission. It is
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intended for static display on a receiver. It is the primary aid to
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listeners in programme service identification and selection. In
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Annex E of :ref:`iec62106`, the RDS specification, there is a full
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description of the correct character encoding for Programme Service
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name strings. Also from RDS specification, PS is usually a single
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eight character text. However, it is also possible to find receivers
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which can scroll strings sized as 8 x N characters. So, this control
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must be configured with steps of 8 characters. The result is it must
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always contain a string with size multiple of 8.
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``V4L2_CID_RDS_TX_RADIO_TEXT (string)``
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Sets the Radio Text info for transmission. It is a textual
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description of what is being broadcasted. RDS Radio Text can be
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applied when broadcaster wishes to transmit longer PS names,
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programme-related information or any other text. In these cases,
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RadioText should be used in addition to ``V4L2_CID_RDS_TX_PS_NAME``.
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The encoding for Radio Text strings is also fully described in Annex
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E of :ref:`iec62106`. The length of Radio Text strings depends on
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which RDS Block is being used to transmit it, either 32 (2A block)
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or 64 (2B block). However, it is also possible to find receivers
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which can scroll strings sized as 32 x N or 64 x N characters. So,
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this control must be configured with steps of 32 or 64 characters.
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The result is it must always contain a string with size multiple of
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32 or 64.
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``V4L2_CID_RDS_TX_MONO_STEREO (boolean)``
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Sets the Mono/Stereo bit of the Decoder Identification code. If set,
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then the audio was recorded as stereo.
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``V4L2_CID_RDS_TX_ARTIFICIAL_HEAD (boolean)``
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Sets the
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`Artificial Head <http://en.wikipedia.org/wiki/Artificial_head>`__
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bit of the Decoder Identification code. If set, then the audio was
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recorded using an artificial head.
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``V4L2_CID_RDS_TX_COMPRESSED (boolean)``
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Sets the Compressed bit of the Decoder Identification code. If set,
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then the audio is compressed.
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``V4L2_CID_RDS_TX_DYNAMIC_PTY (boolean)``
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Sets the Dynamic PTY bit of the Decoder Identification code. If set,
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then the PTY code is dynamically switched.
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``V4L2_CID_RDS_TX_TRAFFIC_ANNOUNCEMENT (boolean)``
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If set, then a traffic announcement is in progress.
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``V4L2_CID_RDS_TX_TRAFFIC_PROGRAM (boolean)``
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If set, then the tuned programme carries traffic announcements.
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``V4L2_CID_RDS_TX_MUSIC_SPEECH (boolean)``
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If set, then this channel broadcasts music. If cleared, then it
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broadcasts speech. If the transmitter doesn't make this distinction,
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then it should be set.
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``V4L2_CID_RDS_TX_ALT_FREQS_ENABLE (boolean)``
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If set, then transmit alternate frequencies.
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``V4L2_CID_RDS_TX_ALT_FREQS (__u32 array)``
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The alternate frequencies in kHz units. The RDS standard allows for
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up to 25 frequencies to be defined. Drivers may support fewer
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frequencies so check the array size.
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``V4L2_CID_AUDIO_LIMITER_ENABLED (boolean)``
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Enables or disables the audio deviation limiter feature. The limiter
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is useful when trying to maximize the audio volume, minimize
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receiver-generated distortion and prevent overmodulation.
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``V4L2_CID_AUDIO_LIMITER_RELEASE_TIME (integer)``
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Sets the audio deviation limiter feature release time. Unit is in
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useconds. Step and range are driver-specific.
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``V4L2_CID_AUDIO_LIMITER_DEVIATION (integer)``
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Configures audio frequency deviation level in Hz. The range and step
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are driver-specific.
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``V4L2_CID_AUDIO_COMPRESSION_ENABLED (boolean)``
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Enables or disables the audio compression feature. This feature
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amplifies signals below the threshold by a fixed gain and compresses
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audio signals above the threshold by the ratio of Threshold/(Gain +
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Threshold).
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``V4L2_CID_AUDIO_COMPRESSION_GAIN (integer)``
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Sets the gain for audio compression feature. It is a dB value. The
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range and step are driver-specific.
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``V4L2_CID_AUDIO_COMPRESSION_THRESHOLD (integer)``
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Sets the threshold level for audio compression freature. It is a dB
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value. The range and step are driver-specific.
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``V4L2_CID_AUDIO_COMPRESSION_ATTACK_TIME (integer)``
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Sets the attack time for audio compression feature. It is a useconds
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value. The range and step are driver-specific.
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``V4L2_CID_AUDIO_COMPRESSION_RELEASE_TIME (integer)``
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Sets the release time for audio compression feature. It is a
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useconds value. The range and step are driver-specific.
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``V4L2_CID_PILOT_TONE_ENABLED (boolean)``
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Enables or disables the pilot tone generation feature.
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``V4L2_CID_PILOT_TONE_DEVIATION (integer)``
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Configures pilot tone frequency deviation level. Unit is in Hz. The
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range and step are driver-specific.
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``V4L2_CID_PILOT_TONE_FREQUENCY (integer)``
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Configures pilot tone frequency value. Unit is in Hz. The range and
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step are driver-specific.
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``V4L2_CID_TUNE_PREEMPHASIS``
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(enum)
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enum v4l2_preemphasis -
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Configures the pre-emphasis value for broadcasting. A pre-emphasis
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filter is applied to the broadcast to accentuate the high audio
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frequencies. Depending on the region, a time constant of either 50
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or 75 useconds is used. The enum v4l2_preemphasis defines possible
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values for pre-emphasis. Here they are:
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.. flat-table::
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:header-rows: 0
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:stub-columns: 0
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* - ``V4L2_PREEMPHASIS_DISABLED``
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- No pre-emphasis is applied.
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* - ``V4L2_PREEMPHASIS_50_uS``
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- A pre-emphasis of 50 uS is used.
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* - ``V4L2_PREEMPHASIS_75_uS``
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- A pre-emphasis of 75 uS is used.
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``V4L2_CID_TUNE_POWER_LEVEL (integer)``
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Sets the output power level for signal transmission. Unit is in
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dBuV. Range and step are driver-specific.
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``V4L2_CID_TUNE_ANTENNA_CAPACITOR (integer)``
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This selects the value of antenna tuning capacitor manually or
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automatically if set to zero. Unit, range and step are
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driver-specific.
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For more details about RDS specification, refer to :ref:`iec62106`
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document, from CENELEC.
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