vidioc-g-modulator.rst

  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{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
184Return Value
185============
186
187On success 0 is returned, on error -1 and the ``errno`` variable is set
188appropriately. The generic error codes are described at the
189:ref:`Generic Error Codes <gen-errors>` chapter.
190
191EINVAL
192    The struct :c:type:`v4l2_modulator` ``index`` is
193    out of bounds.