Documentation/linux_tv/media/v4l/vidioc-g-modulator.rst

   1 .. -*- coding: utf-8; mode: rst -*-
   2
   3 .. _VIDIOC_G_MODULATOR:
   4
   5 ********************************************
   6 ioctl VIDIOC_G_MODULATOR, VIDIOC_S_MODULATOR
   7 ********************************************
   8
   9 Name
  10 ====
  11
  12 VIDIOC_G_MODULATOR - VIDIOC_S_MODULATOR - Get or set modulator attributes
  13
  14
  15 Synopsis
  16 ========
  17
  18 .. cpp:function:: int ioctl( int fd, int request, struct v4l2_modulator *argp )
  19
  20 .. cpp:function:: int ioctl( int fd, int request, const struct v4l2_modulator *argp )
  21
  22
  23 Arguments
  24 =========
  25
  26 ``fd``
  27     File descriptor returned by :ref:`open() <func-open>`.
  28
  29 ``request``
  30     VIDIOC_G_MODULATOR, VIDIOC_S_MODULATOR
  31
  32 ``argp``
  33
  34
  35 Description
  36 ===========
  37
  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
  45 EINVAL.
  46
  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
  53 modulation 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
  57 initialized to zero. The term 'modulator' means SDR transmitter in this
  58 context.
  59
  60 To change the radio frequency the
  61 :ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_FREQUENCY>` ioctl is available.
  62
  63
  64 .. _v4l2-modulator:
  65
  66 .. flat-table:: struct v4l2_modulator
  67     :header-rows:  0
  68     :stub-columns: 0
  69     :widths:       1 1 2 1 1
  70
  71
  72     -  .. row 1
  73
  74        -  __u32
  75
  76        -  ``index``
  77
  78        -  Identifies the modulator, set by the application.
  79
  80     -  .. row 2
  81
  82        -  __u8
  83
  84        -  ``name``\ [32]
  85
  86        -  Name of the modulator, a NUL-terminated ASCII string. This
  87           information is intended for the user.
  88
  89     -  .. row 3
  90
  91        -  __u32
  92
  93        -  ``capability``
  94
  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.
 100
 101     -  .. row 4
 102
 103        -  __u32
 104
 105        -  ``rangelow``
 106
 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.
 111
 112     -  .. row 5
 113
 114        -  __u32
 115
 116        -  ``rangehigh``
 117
 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.
 122
 123     -  .. row 6
 124
 125        -  __u32
 126
 127        -  ``txsubchans``
 128
 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.
 137
 138     -  .. row 7
 139
 140        -  __u32
 141
 142        -  ``type``
 143
 144        -  :cspan:`2` Type of the modulator, see :ref:`v4l2-tuner-type`.
 145
 146     -  .. row 8
 147
 148        -  __u32
 149
 150        -  ``reserved``\ [3]
 151
 152        -  Reserved for future extensions. Drivers and applications must set
 153           the array to zero.
 154
 155
 156
 157 .. _modulator-txsubchans:
 158
 159 .. flat-table:: Modulator Audio Transmission Flags
 160     :header-rows:  0
 161     :stub-columns: 0
 162     :widths:       3 1 4
 163
 164
 165     -  .. row 1
 166
 167        -  ``V4L2_TUNER_SUB_MONO``
 168
 169        -  0x0001
 170
 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``.
 175
 176     -  .. row 2
 177
 178        -  ``V4L2_TUNER_SUB_STEREO``
 179
 180        -  0x0002
 181
 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.
 188
 189     -  .. row 3
 190
 191        -  ``V4L2_TUNER_SUB_LANG1``
 192
 193        -  0x0008
 194
 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
 204           or stereo mode.
 205
 206     -  .. row 4
 207
 208        -  ``V4L2_TUNER_SUB_LANG2``
 209
 210        -  0x0004
 211
 212        -  Same effect as ``V4L2_TUNER_SUB_SAP``.
 213
 214     -  .. row 5
 215
 216        -  ``V4L2_TUNER_SUB_SAP``
 217
 218        -  0x0004
 219
 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.
 236
 237     -  .. row 6
 238
 239        -  ``V4L2_TUNER_SUB_RDS``
 240
 241        -  0x0010
 242
 243        -  Enable the RDS encoder for a radio FM transmitter.
 244
 245
 246 Return Value
 247 ============
 248
 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.
 252
 253 EINVAL
 254     The struct :ref:`v4l2_modulator <v4l2-modulator>` ``index`` is
 255     out of bounds.