1 .. -*- coding: utf-8; mode: rst -*-
3 .. _VIDIOC_G_MODULATOR:
5 ********************************************
6 ioctl VIDIOC_G_MODULATOR, VIDIOC_S_MODULATOR
7 ********************************************
12 VIDIOC_G_MODULATOR - VIDIOC_S_MODULATOR - Get or set modulator attributes
18 .. c:function:: int ioctl( int fd, VIDIOC_G_MODULATOR, struct v4l2_modulator *argp )
19 :name: VIDIOC_G_MODULATOR
21 .. c:function:: int ioctl( int fd, VIDIOC_S_MODULATOR, const struct v4l2_modulator *argp )
22 :name: VIDIOC_S_MODULATOR
29 File descriptor returned by :ref:`open() <func-open>`.
37 To query the attributes of a modulator applications initialize the
38 ``index`` field and zero out the ``reserved`` array of a struct
39 :ref:`v4l2_modulator <v4l2-modulator>` and call the
40 :ref:`VIDIOC_G_MODULATOR <VIDIOC_G_MODULATOR>` ioctl with a pointer to this structure. Drivers
41 fill the rest of the structure or return an ``EINVAL`` error code when the
42 index is out of bounds. To enumerate all modulators applications shall
43 begin at index zero, incrementing by one until the driver returns
46 Modulators have two writable properties, an audio modulation set and the
47 radio frequency. To change the modulated audio subprograms, applications
48 initialize the ``index`` and ``txsubchans`` fields and the ``reserved``
49 array and call the :ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl. Drivers may choose a
50 different audio modulation if the request cannot be satisfied. However
51 this is a write-only ioctl, it does not return the actual audio
54 :ref:`SDR <sdr>` specific modulator types are ``V4L2_TUNER_SDR`` and
55 ``V4L2_TUNER_RF``. For SDR devices ``txsubchans`` field must be
56 initialized to zero. The term 'modulator' means SDR transmitter in this
59 To change the radio frequency the
60 :ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_FREQUENCY>` ioctl is available.
63 .. tabularcolumns:: |p{2.9cm}|p{2.9cm}|p{5.8cm}|p{2.9cm}|p{3.0cm}|
67 .. flat-table:: struct v4l2_modulator
79 - Identifies the modulator, set by the application.
87 - Name of the modulator, a NUL-terminated ASCII string.
89 This information is intended for the user.
97 - Modulator capability flags. No flags are defined for this field,
98 the tuner flags in struct :ref:`v4l2_tuner <v4l2-tuner>` are
99 used accordingly. The audio flags indicate the ability to encode
100 audio subprograms. They will *not* change for example with the
101 current video standard.
109 - The lowest tunable frequency in units of 62.5 KHz, or if the
110 ``capability`` flag ``V4L2_TUNER_CAP_LOW`` is set, in units of
111 62.5 Hz, or if the ``capability`` flag ``V4L2_TUNER_CAP_1HZ`` is
112 set, in units of 1 Hz.
120 - The highest tunable frequency in units of 62.5 KHz, or if the
121 ``capability`` flag ``V4L2_TUNER_CAP_LOW`` is set, in units of
122 62.5 Hz, or if the ``capability`` flag ``V4L2_TUNER_CAP_1HZ`` is
123 set, in units of 1 Hz.
131 - With this field applications can determine how audio sub-carriers
132 shall be modulated. It contains a set of flags as defined in
133 :ref:`modulator-txsubchans`.
137 The tuner ``rxsubchans`` flags are reused, but the
138 semantics are different. Video output devices
139 are assumed to have an analog or PCM audio input with 1-3
140 channels. The ``txsubchans`` flags select one or more channels
141 for modulation, together with some audio subprogram indicator,
142 for example, a stereo pilot tone.
150 - :cspan:`2` Type of the modulator, see :ref:`v4l2-tuner-type`.
158 - Reserved for future extensions.
160 Drivers and applications must set the array to zero.
164 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
166 .. _modulator-txsubchans:
168 .. flat-table:: Modulator Audio Transmission Flags
176 - ``V4L2_TUNER_SUB_MONO``
180 - Modulate channel 1 as mono audio, when the input has more
181 channels, a down-mix of channel 1 and 2. This flag does not
182 combine with ``V4L2_TUNER_SUB_STEREO`` or
183 ``V4L2_TUNER_SUB_LANG1``.
187 - ``V4L2_TUNER_SUB_STEREO``
191 - Modulate channel 1 and 2 as left and right channel of a stereo
192 audio signal. When the input has only one channel or two channels
193 and ``V4L2_TUNER_SUB_SAP`` is also set, channel 1 is encoded as
194 left and right channel. This flag does not combine with
195 ``V4L2_TUNER_SUB_MONO`` or ``V4L2_TUNER_SUB_LANG1``. When the
196 driver does not support stereo audio it shall fall back to mono.
200 - ``V4L2_TUNER_SUB_LANG1``
204 - Modulate channel 1 and 2 as primary and secondary language of a
205 bilingual audio signal. When the input has only one channel it is
206 used for both languages. It is not possible to encode the primary
207 or secondary language only. This flag does not combine with
208 ``V4L2_TUNER_SUB_MONO``, ``V4L2_TUNER_SUB_STEREO`` or
209 ``V4L2_TUNER_SUB_SAP``. If the hardware does not support the
210 respective audio matrix, or the current video standard does not
211 permit bilingual audio the :ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl shall
212 return an ``EINVAL`` error code and the driver shall fall back to mono
217 - ``V4L2_TUNER_SUB_LANG2``
221 - Same effect as ``V4L2_TUNER_SUB_SAP``.
225 - ``V4L2_TUNER_SUB_SAP``
229 - When combined with ``V4L2_TUNER_SUB_MONO`` the first channel is
230 encoded as mono audio, the last channel as Second Audio Program.
231 When the input has only one channel it is used for both audio
232 tracks. When the input has three channels the mono track is a
233 down-mix of channel 1 and 2. When combined with
234 ``V4L2_TUNER_SUB_STEREO`` channel 1 and 2 are encoded as left and
235 right stereo audio, channel 3 as Second Audio Program. When the
236 input has only two channels, the first is encoded as left and
237 right channel and the second as SAP. When the input has only one
238 channel it is used for all audio tracks. It is not possible to
239 encode a Second Audio Program only. This flag must combine with
240 ``V4L2_TUNER_SUB_MONO`` or ``V4L2_TUNER_SUB_STEREO``. If the
241 hardware does not support the respective audio matrix, or the
242 current video standard does not permit SAP the
243 :ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl shall return an ``EINVAL`` error code and
244 driver shall fall back to mono or stereo mode.
248 - ``V4L2_TUNER_SUB_RDS``
252 - Enable the RDS encoder for a radio FM transmitter.
258 On success 0 is returned, on error -1 and the ``errno`` variable is set
259 appropriately. The generic error codes are described at the
260 :ref:`Generic Error Codes <gen-errors>` chapter.
263 The struct :ref:`v4l2_modulator <v4l2-modulator>` ``index`` is