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1.. Permission is granted to copy, distribute and/or modify this
2.. document under the terms of the GNU Free Documentation License,
3.. Version 1.1 or any later version published by the Free Software
4.. Foundation, with no Invariant Sections, no Front-Cover Texts
5.. and no Back-Cover Texts. A copy of the license is included at
6.. Documentation/media/uapi/fdl-appendix.rst.
7..
8.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
9
10.. _VIDIOC_G_MODULATOR:
11
12********************************************
13ioctl VIDIOC_G_MODULATOR, VIDIOC_S_MODULATOR
14********************************************
15
16Name
17====
18
19VIDIOC_G_MODULATOR - VIDIOC_S_MODULATOR - Get or set modulator attributes
20
21
22Synopsis
23========
24
25.. c:function:: int ioctl( int fd, VIDIOC_G_MODULATOR, struct v4l2_modulator *argp )
26 :name: VIDIOC_G_MODULATOR
27
28.. c:function:: int ioctl( int fd, VIDIOC_S_MODULATOR, const struct v4l2_modulator *argp )
29 :name: VIDIOC_S_MODULATOR
30
31
32Arguments
33=========
34
35``fd``
36 File descriptor returned by :ref:`open() <func-open>`.
37
38``argp``
39 Pointer to struct :c:type:`v4l2_modulator`.
40
41
42Description
43===========
44
45To query the attributes of a modulator applications initialize the
46``index`` field and zero out the ``reserved`` array of a struct
47:c:type:`v4l2_modulator` and call the
48:ref:`VIDIOC_G_MODULATOR <VIDIOC_G_MODULATOR>` ioctl with a pointer to this structure. Drivers
49fill the rest of the structure or return an ``EINVAL`` error code when the
50index is out of bounds. To enumerate all modulators applications shall
51begin at index zero, incrementing by one until the driver returns
52EINVAL.
53
54Modulators have two writable properties, an audio modulation set and the
55radio frequency. To change the modulated audio subprograms, applications
56initialize the ``index`` and ``txsubchans`` fields and the ``reserved``
57array and call the :ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl. Drivers may choose a
58different audio modulation if the request cannot be satisfied. However
59this is a write-only ioctl, it does not return the actual audio
60modulation selected.
61
62:ref:`SDR <sdr>` specific modulator types are ``V4L2_TUNER_SDR`` and
63``V4L2_TUNER_RF``. For SDR devices ``txsubchans`` field must be
64initialized to zero. The term 'modulator' means SDR transmitter in this
65context.
66
67To change the radio frequency the
68:ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_FREQUENCY>` ioctl is available.
69
70
71.. tabularcolumns:: |p{2.9cm}|p{2.9cm}|p{5.8cm}|p{2.9cm}|p{3.0cm}|
72
73.. c:type:: v4l2_modulator
74
75.. flat-table:: struct v4l2_modulator
76 :header-rows: 0
77 :stub-columns: 0
78 :widths: 1 1 2 1 1
79
80 * - __u32
81 - ``index``
82 - Identifies the modulator, set by the application.
83 * - __u8
84 - ``name``\ [32]
85 - Name of the modulator, a NUL-terminated ASCII string.
86
87 This information is intended for the user.
88 * - __u32
89 - ``capability``
90 - Modulator capability flags. No flags are defined for this field,
91 the tuner flags in struct :c:type:`v4l2_tuner` are
92 used accordingly. The audio flags indicate the ability to encode
93 audio subprograms. They will *not* change for example with the
94 current video standard.
95 * - __u32
96 - ``rangelow``
97 - The lowest tunable frequency in units of 62.5 KHz, or if the
98 ``capability`` flag ``V4L2_TUNER_CAP_LOW`` is set, in units of
99 62.5 Hz, or if the ``capability`` flag ``V4L2_TUNER_CAP_1HZ`` is
100 set, in units of 1 Hz.
101 * - __u32
102 - ``rangehigh``
103 - The highest tunable frequency in units of 62.5 KHz, or if the
104 ``capability`` flag ``V4L2_TUNER_CAP_LOW`` is set, in units of
105 62.5 Hz, or if the ``capability`` flag ``V4L2_TUNER_CAP_1HZ`` is
106 set, in units of 1 Hz.
107 * - __u32
108 - ``txsubchans``
109 - With this field applications can determine how audio sub-carriers
110 shall be modulated. It contains a set of flags as defined in
111 :ref:`modulator-txsubchans`.
112
113 .. note::
114
115 The tuner ``rxsubchans`` flags are reused, but the
116 semantics are different. Video output devices
117 are assumed to have an analog or PCM audio input with 1-3
118 channels. The ``txsubchans`` flags select one or more channels
119 for modulation, together with some audio subprogram indicator,
120 for example, a stereo pilot tone.
121 * - __u32
122 - ``type``
123 - :cspan:`2` Type of the modulator, see :c:type:`v4l2_tuner_type`.
124 * - __u32
125 - ``reserved``\ [3]
126 - Reserved for future extensions.
127
128 Drivers and applications must set the array to zero.
129
130
131
132.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
133
134.. _modulator-txsubchans:
135
136.. flat-table:: Modulator Audio Transmission Flags
137 :header-rows: 0
138 :stub-columns: 0
139 :widths: 3 1 4
140
141 * - ``V4L2_TUNER_SUB_MONO``
142 - 0x0001
143 - Modulate channel 1 as mono audio, when the input has more
144 channels, a down-mix of channel 1 and 2. This flag does not
145 combine with ``V4L2_TUNER_SUB_STEREO`` or
146 ``V4L2_TUNER_SUB_LANG1``.
147 * - ``V4L2_TUNER_SUB_STEREO``
148 - 0x0002
149 - Modulate channel 1 and 2 as left and right channel of a stereo
150 audio signal. When the input has only one channel or two channels
151 and ``V4L2_TUNER_SUB_SAP`` is also set, channel 1 is encoded as
152 left and right channel. This flag does not combine with
153 ``V4L2_TUNER_SUB_MONO`` or ``V4L2_TUNER_SUB_LANG1``. When the
154 driver does not support stereo audio it shall fall back to mono.
155 * - ``V4L2_TUNER_SUB_LANG1``
156 - 0x0008
157 - Modulate channel 1 and 2 as primary and secondary language of a
158 bilingual audio signal. When the input has only one channel it is
159 used for both languages. It is not possible to encode the primary
160 or secondary language only. This flag does not combine with
161 ``V4L2_TUNER_SUB_MONO``, ``V4L2_TUNER_SUB_STEREO`` or
162 ``V4L2_TUNER_SUB_SAP``. If the hardware does not support the
163 respective audio matrix, or the current video standard does not
164 permit bilingual audio the :ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl shall
165 return an ``EINVAL`` error code and the driver shall fall back to mono
166 or stereo mode.
167 * - ``V4L2_TUNER_SUB_LANG2``
168 - 0x0004
169 - Same effect as ``V4L2_TUNER_SUB_SAP``.
170 * - ``V4L2_TUNER_SUB_SAP``
171 - 0x0004
172 - When combined with ``V4L2_TUNER_SUB_MONO`` the first channel is
173 encoded as mono audio, the last channel as Second Audio Program.
174 When the input has only one channel it is used for both audio
175 tracks. When the input has three channels the mono track is a
176 down-mix of channel 1 and 2. When combined with
177 ``V4L2_TUNER_SUB_STEREO`` channel 1 and 2 are encoded as left and
178 right stereo audio, channel 3 as Second Audio Program. When the
179 input has only two channels, the first is encoded as left and
180 right channel and the second as SAP. When the input has only one
181 channel it is used for all audio tracks. It is not possible to
182 encode a Second Audio Program only. This flag must combine with
183 ``V4L2_TUNER_SUB_MONO`` or ``V4L2_TUNER_SUB_STEREO``. If the
184 hardware does not support the respective audio matrix, or the
185 current video standard does not permit SAP the
186 :ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl shall return an ``EINVAL`` error code and
187 driver shall fall back to mono or stereo mode.
188 * - ``V4L2_TUNER_SUB_RDS``
189 - 0x0010
190 - Enable the RDS encoder for a radio FM transmitter.
191
192
193Return Value
194============
195
196On success 0 is returned, on error -1 and the ``errno`` variable is set
197appropriately. The generic error codes are described at the
198:ref:`Generic Error Codes <gen-errors>` chapter.
199
200EINVAL
201 The struct :c:type:`v4l2_modulator` ``index`` is
202 out of bounds.