1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2 .. c:namespace:: V4L
3
4 .. _VIDIOC_G_MODULATOR:
5
6 ********************************************
7 ioctl VIDIOC_G_MODULATOR, VIDIOC_S_MODULATOR
8 ********************************************
9
10 Name
11 ====
12
13 VIDIOC_G_MODULATOR - VIDIOC_S_MODULATOR - Get or set modulator attributes
14
15 Synopsis
16 ========
17
18 .. c:macro:: VIDIOC_G_MODULATOR
19
20 ``int ioctl(int fd, VIDIOC_G_MODULATOR, struct v4l2_modulator *argp)``
21
22 .. c:macro:: VIDIOC_S_MODULATOR
23
24 ``int ioctl(int fd, VIDIOC_S_MODULATOR, const struct v4l2_modulator *argp)``
25
26 Arguments
27 =========
28
29 ``fd``
30 File descriptor returned by :c:func:`open()`.
31
32 ``argp``
33 Pointer to struct :c:type:`v4l2_modulator`.
34
35 Description
36 ===========
37
38 To query the attributes of a modulator applications initialize the
39 ``index`` field and zero out the ``reserved`` array of a struct
40 :c:type:`v4l2_modulator` and call the
41 :ref:`VIDIOC_G_MODULATOR <VIDIOC_G_MODULATOR>` ioctl with a pointer to this structure. Drivers
42 fill the rest of the structure or return an ``EINVAL`` error code when the
43 index is out of bounds. To enumerate all modulators applications shall
44 begin at index zero, incrementing by one until the driver returns
45 EINVAL.
46
47 Modulators have two writable properties, an audio modulation set and the
48 radio frequency. To change the modulated audio subprograms, applications
49 initialize the ``index`` and ``txsubchans`` fields and the ``reserved``
50 array and call the :ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl. Drivers may choose a
51 different audio modulation if the request cannot be satisfied. However
52 this is a write-only ioctl, it does not return the actual audio
53 modulation selected.
54
55 :ref:`SDR <sdr>` specific modulator types are ``V4L2_TUNER_SDR`` and
56 ``V4L2_TUNER_RF``. For SDR devices ``txsubchans`` field must be
57 initialized to zero. The term 'modulator' means SDR transmitter in this
58 context.
59
60 To change the radio frequency the
61 :ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_FREQUENCY>` ioctl is available.
62
63 .. tabularcolumns:: |p{2.9cm}|p{2.9cm}|p{5.8cm}|p{2.9cm}|p{2.4cm}|
64
65 .. c:type:: v4l2_modulator
66
67 .. flat-table:: struct v4l2_modulator
68 :header-rows: 0
69 :stub-columns: 0
70 :widths: 1 1 2 1 1
71
72 * - __u32
73 - ``index``
74 - Identifies the modulator, set by the application.
75 * - __u8
76 - ``name``\ [32]
77 - Name of the modulator, a NUL-terminated ASCII string.
78
79 This information is intended for the user.
80 * - __u32
81 - ``capability``
82 - Modulator capability flags. No flags are defined for this field,
83 the tuner flags in struct :c:type:`v4l2_tuner` are
84 used accordingly. The audio flags indicate the ability to encode
85 audio subprograms. They will *not* change for example with the
86 current video standard.
87 * - __u32
88 - ``rangelow``
89 - The lowest tunable frequency in units of 62.5 KHz, or if the
90 ``capability`` flag ``V4L2_TUNER_CAP_LOW`` is set, in units of
91 62.5 Hz, or if the ``capability`` flag ``V4L2_TUNER_CAP_1HZ`` is
92 set, in units of 1 Hz.
93 * - __u32
94 - ``rangehigh``
95 - The highest tunable frequency in units of 62.5 KHz, or if the
96 ``capability`` flag ``V4L2_TUNER_CAP_LOW`` is set, in units of
97 62.5 Hz, or if the ``capability`` flag ``V4L2_TUNER_CAP_1HZ`` is
98 set, in units of 1 Hz.
99 * - __u32
100 - ``txsubchans``
101 - With this field applications can determine how audio sub-carriers
102 shall be modulated. It contains a set of flags as defined in
103 :ref:`modulator-txsubchans`.
104
105 .. note::
106
107 The tuner ``rxsubchans`` flags are reused, but the
108 semantics are different. Video output devices
109 are assumed to have an analog or PCM audio input with 1-3
110 channels. The ``txsubchans`` flags select one or more channels
111 for modulation, together with some audio subprogram indicator,
112 for example, a stereo pilot tone.
113 * - __u32
114 - ``type``
115 - :cspan:`2` Type of the modulator, see :c:type:`v4l2_tuner_type`.
116 * - __u32
117 - ``reserved``\ [3]
118 - Reserved for future extensions.
119
120 Drivers and applications must set the array to zero.
121
122 .. tabularcolumns:: |p{6.0cm}|p{2.0cm}|p{9.3cm}|
123
124 .. cssclass:: longtable
125
126 .. _modulator-txsubchans:
127
128 .. flat-table:: Modulator Audio Transmission Flags
129 :header-rows: 0
130 :stub-columns: 0
131 :widths: 3 1 4
132
133 * - ``V4L2_TUNER_SUB_MONO``
134 - 0x0001
135 - Modulate channel 1 as mono audio, when the input has more
136 channels, a down-mix of channel 1 and 2. This flag does not
137 combine with ``V4L2_TUNER_SUB_STEREO`` or
138 ``V4L2_TUNER_SUB_LANG1``.
139 * - ``V4L2_TUNER_SUB_STEREO``
140 - 0x0002
141 - Modulate channel 1 and 2 as left and right channel of a stereo
142 audio signal. When the input has only one channel or two channels
143 and ``V4L2_TUNER_SUB_SAP`` is also set, channel 1 is encoded as
144 left and right channel. This flag does not combine with
145 ``V4L2_TUNER_SUB_MONO`` or ``V4L2_TUNER_SUB_LANG1``. When the
146 driver does not support stereo audio it shall fall back to mono.
147 * - ``V4L2_TUNER_SUB_LANG1``
148 - 0x0008
149 - Modulate channel 1 and 2 as primary and secondary language of a
150 bilingual audio signal. When the input has only one channel it is
151 used for both languages. It is not possible to encode the primary
152 or secondary language only. This flag does not combine with
153 ``V4L2_TUNER_SUB_MONO``, ``V4L2_TUNER_SUB_STEREO`` or
154 ``V4L2_TUNER_SUB_SAP``. If the hardware does not support the
155 respective audio matrix, or the current video standard does not
156 permit bilingual audio the :ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl shall
157 return an ``EINVAL`` error code and the driver shall fall back to mono
158 or stereo mode.
159 * - ``V4L2_TUNER_SUB_LANG2``
160 - 0x0004
161 - Same effect as ``V4L2_TUNER_SUB_SAP``.
162 * - ``V4L2_TUNER_SUB_SAP``
163 - 0x0004
164 - When combined with ``V4L2_TUNER_SUB_MONO`` the first channel is
165 encoded as mono audio, the last channel as Second Audio Program.
166 When the input has only one channel it is used for both audio
167 tracks. When the input has three channels the mono track is a
168 down-mix of channel 1 and 2. When combined with
169 ``V4L2_TUNER_SUB_STEREO`` channel 1 and 2 are encoded as left and
170 right stereo audio, channel 3 as Second Audio Program. When the
171 input has only two channels, the first is encoded as left and
172 right channel and the second as SAP. When the input has only one
173 channel it is used for all audio tracks. It is not possible to
174 encode a Second Audio Program only. This flag must combine with
175 ``V4L2_TUNER_SUB_MONO`` or ``V4L2_TUNER_SUB_STEREO``. If the
176 hardware does not support the respective audio matrix, or the
177 current video standard does not permit SAP the
178 :ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl shall return an ``EINVAL`` error code and
179 driver shall fall back to mono or stereo mode.
180 * - ``V4L2_TUNER_SUB_RDS``
181 - 0x0010
182 - Enable the RDS encoder for a radio FM transmitter.
183
184 Return Value
185 ============
186
187 On success 0 is returned, on error -1 and the ``errno`` variable is set
188 appropriately. The generic error codes are described at the
189 :ref:`Generic Error Codes <gen-errors>` chapter.
190
191 EINVAL
192 The struct :c:type:`v4l2_modulator` ``index`` is
193 out of bounds.
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