1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2.. c:namespace:: V4L
3
4.. _VIDIOC_G_MODULATOR:
5
6********************************************
7ioctl VIDIOC_G_MODULATOR, VIDIOC_S_MODULATOR
8********************************************
9
10Name
11====
12
13VIDIOC_G_MODULATOR - VIDIOC_S_MODULATOR - Get or set modulator attributes
14
15Synopsis
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
26Arguments
27=========
28
29``fd``
30    File descriptor returned by :c:func:`open()`.
31
32``argp``
33    Pointer to struct :c:type:`v4l2_modulator`.
34
35Description
36===========
37
38To 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
42fill the rest of the structure or return an ``EINVAL`` error code when the
43index is out of bounds. To enumerate all modulators applications shall
44begin at index zero, incrementing by one until the driver returns
45EINVAL.
46
47Modulators have two writable properties, an audio modulation set and the
48radio frequency. To change the modulated audio subprograms, applications
49initialize the ``index`` and ``txsubchans`` fields and the ``reserved``
50array and call the :ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl. Drivers may choose a
51different audio modulation if the request cannot be satisfied. However
52this is a write-only ioctl, it does not return the actual audio
53modulation 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
57initialized to zero. The term 'modulator' means SDR transmitter in this
58context.
59
60To 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{3.0cm}|
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
123.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
124
125.. _modulator-txsubchans:
126
127.. flat-table:: Modulator Audio Transmission Flags
128    :header-rows:  0
129    :stub-columns: 0
130    :widths:       3 1 4
131
132    * - ``V4L2_TUNER_SUB_MONO``
133      - 0x0001
134      - Modulate channel 1 as mono audio, when the input has more
135	channels, a down-mix of channel 1 and 2. This flag does not
136	combine with ``V4L2_TUNER_SUB_STEREO`` or
137	``V4L2_TUNER_SUB_LANG1``.
138    * - ``V4L2_TUNER_SUB_STEREO``
139      - 0x0002
140      - Modulate channel 1 and 2 as left and right channel of a stereo
141	audio signal. When the input has only one channel or two channels
142	and ``V4L2_TUNER_SUB_SAP`` is also set, channel 1 is encoded as
143	left and right channel. This flag does not combine with
144	``V4L2_TUNER_SUB_MONO`` or ``V4L2_TUNER_SUB_LANG1``. When the
145	driver does not support stereo audio it shall fall back to mono.
146    * - ``V4L2_TUNER_SUB_LANG1``
147      - 0x0008
148      - Modulate channel 1 and 2 as primary and secondary language of a
149	bilingual audio signal. When the input has only one channel it is
150	used for both languages. It is not possible to encode the primary
151	or secondary language only. This flag does not combine with
152	``V4L2_TUNER_SUB_MONO``, ``V4L2_TUNER_SUB_STEREO`` or
153	``V4L2_TUNER_SUB_SAP``. If the hardware does not support the
154	respective audio matrix, or the current video standard does not
155	permit bilingual audio the :ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl shall
156	return an ``EINVAL`` error code and the driver shall fall back to mono
157	or stereo mode.
158    * - ``V4L2_TUNER_SUB_LANG2``
159      - 0x0004
160      - Same effect as ``V4L2_TUNER_SUB_SAP``.
161    * - ``V4L2_TUNER_SUB_SAP``
162      - 0x0004
163      - When combined with ``V4L2_TUNER_SUB_MONO`` the first channel is
164	encoded as mono audio, the last channel as Second Audio Program.
165	When the input has only one channel it is used for both audio
166	tracks. When the input has three channels the mono track is a
167	down-mix of channel 1 and 2. When combined with
168	``V4L2_TUNER_SUB_STEREO`` channel 1 and 2 are encoded as left and
169	right stereo audio, channel 3 as Second Audio Program. When the
170	input has only two channels, the first is encoded as left and
171	right channel and the second as SAP. When the input has only one
172	channel it is used for all audio tracks. It is not possible to
173	encode a Second Audio Program only. This flag must combine with
174	``V4L2_TUNER_SUB_MONO`` or ``V4L2_TUNER_SUB_STEREO``. If the
175	hardware does not support the respective audio matrix, or the
176	current video standard does not permit SAP the
177	:ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl shall return an ``EINVAL`` error code and
178	driver shall fall back to mono or stereo mode.
179    * - ``V4L2_TUNER_SUB_RDS``
180      - 0x0010
181      - Enable the RDS encoder for a radio FM transmitter.
182
183Return Value
184============
185
186On success 0 is returned, on error -1 and the ``errno`` variable is set
187appropriately. The generic error codes are described at the
188:ref:`Generic Error Codes <gen-errors>` chapter.
189
190EINVAL
191    The struct :c:type:`v4l2_modulator` ``index`` is
192    out of bounds.
193