1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
5 ********************************
6 FM Transmitter Control Reference
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9 The FM Transmitter (FM_TX) class includes controls for common features
10 of FM transmissions capable devices. Currently this class includes
11 parameters for audio compression, pilot tone generation, audio deviation
12 limiter, RDS transmission and tuning power features.
20 ``V4L2_CID_FM_TX_CLASS (class)``
21 The FM_TX class descriptor. Calling
22 :ref:`VIDIOC_QUERYCTRL` for this control will
23 return a description of this control class.
25 ``V4L2_CID_RDS_TX_DEVIATION (integer)``
26 Configures RDS signal frequency deviation level in Hz. The range and
27 step are driver-specific.
29 ``V4L2_CID_RDS_TX_PI (integer)``
30 Sets the RDS Programme Identification field for transmission.
32 ``V4L2_CID_RDS_TX_PTY (integer)``
33 Sets the RDS Programme Type field for transmission. This encodes up
34 to 31 pre-defined programme types.
36 ``V4L2_CID_RDS_TX_PS_NAME (string)``
37 Sets the Programme Service name (PS_NAME) for transmission. It is
38 intended for static display on a receiver. It is the primary aid to
39 listeners in programme service identification and selection. In
40 Annex E of :ref:`iec62106`, the RDS specification, there is a full
41 description of the correct character encoding for Programme Service
42 name strings. Also from RDS specification, PS is usually a single
43 eight character text. However, it is also possible to find receivers
44 which can scroll strings sized as 8 x N characters. So, this control
45 must be configured with steps of 8 characters. The result is it must
46 always contain a string with size multiple of 8.
48 ``V4L2_CID_RDS_TX_RADIO_TEXT (string)``
49 Sets the Radio Text info for transmission. It is a textual
50 description of what is being broadcasted. RDS Radio Text can be
51 applied when broadcaster wishes to transmit longer PS names,
52 programme-related information or any other text. In these cases,
53 RadioText should be used in addition to ``V4L2_CID_RDS_TX_PS_NAME``.
54 The encoding for Radio Text strings is also fully described in Annex
55 E of :ref:`iec62106`. The length of Radio Text strings depends on
56 which RDS Block is being used to transmit it, either 32 (2A block)
57 or 64 (2B block). However, it is also possible to find receivers
58 which can scroll strings sized as 32 x N or 64 x N characters. So,
59 this control must be configured with steps of 32 or 64 characters.
60 The result is it must always contain a string with size multiple of
63 ``V4L2_CID_RDS_TX_MONO_STEREO (boolean)``
64 Sets the Mono/Stereo bit of the Decoder Identification code. If set,
65 then the audio was recorded as stereo.
67 ``V4L2_CID_RDS_TX_ARTIFICIAL_HEAD (boolean)``
69 `Artificial Head <http://en.wikipedia.org/wiki/Artificial_head>`__
70 bit of the Decoder Identification code. If set, then the audio was
71 recorded using an artificial head.
73 ``V4L2_CID_RDS_TX_COMPRESSED (boolean)``
74 Sets the Compressed bit of the Decoder Identification code. If set,
75 then the audio is compressed.
77 ``V4L2_CID_RDS_TX_DYNAMIC_PTY (boolean)``
78 Sets the Dynamic PTY bit of the Decoder Identification code. If set,
79 then the PTY code is dynamically switched.
81 ``V4L2_CID_RDS_TX_TRAFFIC_ANNOUNCEMENT (boolean)``
82 If set, then a traffic announcement is in progress.
84 ``V4L2_CID_RDS_TX_TRAFFIC_PROGRAM (boolean)``
85 If set, then the tuned programme carries traffic announcements.
87 ``V4L2_CID_RDS_TX_MUSIC_SPEECH (boolean)``
88 If set, then this channel broadcasts music. If cleared, then it
89 broadcasts speech. If the transmitter doesn't make this distinction,
90 then it should be set.
92 ``V4L2_CID_RDS_TX_ALT_FREQS_ENABLE (boolean)``
93 If set, then transmit alternate frequencies.
95 ``V4L2_CID_RDS_TX_ALT_FREQS (__u32 array)``
96 The alternate frequencies in kHz units. The RDS standard allows for
97 up to 25 frequencies to be defined. Drivers may support fewer
98 frequencies so check the array size.
100 ``V4L2_CID_AUDIO_LIMITER_ENABLED (boolean)``
101 Enables or disables the audio deviation limiter feature. The limiter
102 is useful when trying to maximize the audio volume, minimize
103 receiver-generated distortion and prevent overmodulation.
105 ``V4L2_CID_AUDIO_LIMITER_RELEASE_TIME (integer)``
106 Sets the audio deviation limiter feature release time. Unit is in
107 useconds. Step and range are driver-specific.
109 ``V4L2_CID_AUDIO_LIMITER_DEVIATION (integer)``
110 Configures audio frequency deviation level in Hz. The range and step
113 ``V4L2_CID_AUDIO_COMPRESSION_ENABLED (boolean)``
114 Enables or disables the audio compression feature. This feature
115 amplifies signals below the threshold by a fixed gain and compresses
116 audio signals above the threshold by the ratio of Threshold/(Gain +
119 ``V4L2_CID_AUDIO_COMPRESSION_GAIN (integer)``
120 Sets the gain for audio compression feature. It is a dB value. The
121 range and step are driver-specific.
123 ``V4L2_CID_AUDIO_COMPRESSION_THRESHOLD (integer)``
124 Sets the threshold level for audio compression freature. It is a dB
125 value. The range and step are driver-specific.
127 ``V4L2_CID_AUDIO_COMPRESSION_ATTACK_TIME (integer)``
128 Sets the attack time for audio compression feature. It is a useconds
129 value. The range and step are driver-specific.
131 ``V4L2_CID_AUDIO_COMPRESSION_RELEASE_TIME (integer)``
132 Sets the release time for audio compression feature. It is a
133 useconds value. The range and step are driver-specific.
135 ``V4L2_CID_PILOT_TONE_ENABLED (boolean)``
136 Enables or disables the pilot tone generation feature.
138 ``V4L2_CID_PILOT_TONE_DEVIATION (integer)``
139 Configures pilot tone frequency deviation level. Unit is in Hz. The
140 range and step are driver-specific.
142 ``V4L2_CID_PILOT_TONE_FREQUENCY (integer)``
143 Configures pilot tone frequency value. Unit is in Hz. The range and
144 step are driver-specific.
146 ``V4L2_CID_TUNE_PREEMPHASIS``
149 enum v4l2_preemphasis -
150 Configures the pre-emphasis value for broadcasting. A pre-emphasis
151 filter is applied to the broadcast to accentuate the high audio
152 frequencies. Depending on the region, a time constant of either 50
153 or 75 useconds is used. The enum v4l2_preemphasis defines possible
154 values for pre-emphasis. Here they are:
162 * - ``V4L2_PREEMPHASIS_DISABLED``
163 - No pre-emphasis is applied.
164 * - ``V4L2_PREEMPHASIS_50_uS``
165 - A pre-emphasis of 50 uS is used.
166 * - ``V4L2_PREEMPHASIS_75_uS``
167 - A pre-emphasis of 75 uS is used.
171 ``V4L2_CID_TUNE_POWER_LEVEL (integer)``
172 Sets the output power level for signal transmission. Unit is in
173 dBuV. Range and step are driver-specific.
175 ``V4L2_CID_TUNE_ANTENNA_CAPACITOR (integer)``
176 This selects the value of antenna tuning capacitor manually or
177 automatically if set to zero. Unit, range and step are
180 For more details about RDS specification, refer to :ref:`iec62106`
181 document, from CENELEC.