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 .. cpp:function:: int ioctl( int fd, int request, struct v4l2_modulator *argp )
20 .. cpp:function:: int ioctl( int fd, int request, const struct v4l2_modulator *argp )
27 File descriptor returned by :ref:`open() <func-open>`.
30 VIDIOC_G_MODULATOR, VIDIOC_S_MODULATOR
38 To query the attributes of a modulator applications initialize the
39 ``index`` field and zero out the ``reserved`` array of a struct
40 :ref:`v4l2_modulator <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
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
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
60 To change the radio frequency the
61 :ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_FREQUENCY>` ioctl is available.
66 .. flat-table:: struct v4l2_modulator
78 - Identifies the modulator, set by the application.
86 - Name of the modulator, a NUL-terminated ASCII string. This
87 information is intended for the user.
95 - Modulator capability flags. No flags are defined for this field,
96 the tuner flags in struct :ref:`v4l2_tuner <v4l2-tuner>` are
97 used accordingly. The audio flags indicate the ability to encode
98 audio subprograms. They will *not* change for example with the
99 current video standard.
107 - The lowest tunable frequency in units of 62.5 KHz, or if the
108 ``capability`` flag ``V4L2_TUNER_CAP_LOW`` is set, in units of
109 62.5 Hz, or if the ``capability`` flag ``V4L2_TUNER_CAP_1HZ`` is
110 set, in units of 1 Hz.
118 - The highest tunable frequency in units of 62.5 KHz, or if the
119 ``capability`` flag ``V4L2_TUNER_CAP_LOW`` is set, in units of
120 62.5 Hz, or if the ``capability`` flag ``V4L2_TUNER_CAP_1HZ`` is
121 set, in units of 1 Hz.
129 - With this field applications can determine how audio sub-carriers
130 shall be modulated. It contains a set of flags as defined in
131 :ref:`modulator-txsubchans`. Note the tuner ``rxsubchans`` flags
132 are reused, but the semantics are different. Video output devices
133 are assumed to have an analog or PCM audio input with 1-3
134 channels. The ``txsubchans`` flags select one or more channels for
135 modulation, together with some audio subprogram indicator, for
136 example a stereo pilot tone.
144 - :cspan:`2` Type of the modulator, see :ref:`v4l2-tuner-type`.
152 - Reserved for future extensions. Drivers and applications must set
157 .. _modulator-txsubchans:
159 .. flat-table:: Modulator Audio Transmission Flags
167 - ``V4L2_TUNER_SUB_MONO``
171 - Modulate channel 1 as mono audio, when the input has more
172 channels, a down-mix of channel 1 and 2. This flag does not
173 combine with ``V4L2_TUNER_SUB_STEREO`` or
174 ``V4L2_TUNER_SUB_LANG1``.
178 - ``V4L2_TUNER_SUB_STEREO``
182 - Modulate channel 1 and 2 as left and right channel of a stereo
183 audio signal. When the input has only one channel or two channels
184 and ``V4L2_TUNER_SUB_SAP`` is also set, channel 1 is encoded as
185 left and right channel. This flag does not combine with
186 ``V4L2_TUNER_SUB_MONO`` or ``V4L2_TUNER_SUB_LANG1``. When the
187 driver does not support stereo audio it shall fall back to mono.
191 - ``V4L2_TUNER_SUB_LANG1``
195 - Modulate channel 1 and 2 as primary and secondary language of a
196 bilingual audio signal. When the input has only one channel it is
197 used for both languages. It is not possible to encode the primary
198 or secondary language only. This flag does not combine with
199 ``V4L2_TUNER_SUB_MONO``, ``V4L2_TUNER_SUB_STEREO`` or
200 ``V4L2_TUNER_SUB_SAP``. If the hardware does not support the
201 respective audio matrix, or the current video standard does not
202 permit bilingual audio the :ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl shall
203 return an ``EINVAL`` error code and the driver shall fall back to mono
208 - ``V4L2_TUNER_SUB_LANG2``
212 - Same effect as ``V4L2_TUNER_SUB_SAP``.
216 - ``V4L2_TUNER_SUB_SAP``
220 - When combined with ``V4L2_TUNER_SUB_MONO`` the first channel is
221 encoded as mono audio, the last channel as Second Audio Program.
222 When the input has only one channel it is used for both audio
223 tracks. When the input has three channels the mono track is a
224 down-mix of channel 1 and 2. When combined with
225 ``V4L2_TUNER_SUB_STEREO`` channel 1 and 2 are encoded as left and
226 right stereo audio, channel 3 as Second Audio Program. When the
227 input has only two channels, the first is encoded as left and
228 right channel and the second as SAP. When the input has only one
229 channel it is used for all audio tracks. It is not possible to
230 encode a Second Audio Program only. This flag must combine with
231 ``V4L2_TUNER_SUB_MONO`` or ``V4L2_TUNER_SUB_STEREO``. If the
232 hardware does not support the respective audio matrix, or the
233 current video standard does not permit SAP the
234 :ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl shall return an ``EINVAL`` error code and
235 driver shall fall back to mono or stereo mode.
239 - ``V4L2_TUNER_SUB_RDS``
243 - Enable the RDS encoder for a radio FM transmitter.
249 On success 0 is returned, on error -1 and the ``errno`` variable is set
250 appropriately. The generic error codes are described at the
251 :ref:`Generic Error Codes <gen-errors>` chapter.
254 The struct :ref:`v4l2_modulator <v4l2-modulator>` ``index`` is