Documentation/linux_tv/media/v4l/tuner.rst

   1 .. -*- coding: utf-8; mode: rst -*-
   2
   3 .. _tuner:
   4
   5 *********************
   6 Tuners and Modulators
   7 *********************
   8
   9
  10 Tuners
  11 ======
  12
  13 Video input devices can have one or more tuners demodulating a RF
  14 signal. Each tuner is associated with one or more video inputs,
  15 depending on the number of RF connectors on the tuner. The ``type``
  16 field of the respective struct :ref:`v4l2_input <v4l2-input>`
  17 returned by the :ref:`VIDIOC_ENUMINPUT <VIDIOC_ENUMINPUT>` ioctl is
  18 set to ``V4L2_INPUT_TYPE_TUNER`` and its ``tuner`` field contains the
  19 index number of the tuner.
  20
  21 Radio input devices have exactly one tuner with index zero, no video
  22 inputs.
  23
  24 To query and change tuner properties applications use the
  25 :ref:`VIDIOC_G_TUNER <VIDIOC_G_TUNER>` and
  26 :ref:`VIDIOC_S_TUNER <VIDIOC_G_TUNER>` ioctls, respectively. The
  27 struct :ref:`v4l2_tuner <v4l2-tuner>` returned by ``VIDIOC_G_TUNER``
  28 also contains signal status information applicable when the tuner of the
  29 current video or radio input is queried. Note that ``VIDIOC_S_TUNER``
  30 does not switch the current tuner, when there is more than one at all.
  31 The tuner is solely determined by the current video input. Drivers must
  32 support both ioctls and set the ``V4L2_CAP_TUNER`` flag in the struct
  33 :ref:`v4l2_capability <v4l2-capability>` returned by the
  34 :ref:`VIDIOC_QUERYCAP <VIDIOC_QUERYCAP>` ioctl when the device has
  35 one or more tuners.
  36
  37
  38 Modulators
  39 ==========
  40
  41 Video output devices can have one or more modulators, uh, modulating a
  42 video signal for radiation or connection to the antenna input of a TV
  43 set or video recorder. Each modulator is associated with one or more
  44 video outputs, depending on the number of RF connectors on the
  45 modulator. The ``type`` field of the respective struct
  46 :ref:`v4l2_output <v4l2-output>` returned by the
  47 :ref:`VIDIOC_ENUMOUTPUT <VIDIOC_ENUMOUTPUT>` ioctl is set to
  48 ``V4L2_OUTPUT_TYPE_MODULATOR`` and its ``modulator`` field contains the
  49 index number of the modulator.
  50
  51 Radio output devices have exactly one modulator with index zero, no
  52 video outputs.
  53
  54 A video or radio device cannot support both a tuner and a modulator. Two
  55 separate device nodes will have to be used for such hardware, one that
  56 supports the tuner functionality and one that supports the modulator
  57 functionality. The reason is a limitation with the
  58 :ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_FREQUENCY>` ioctl where you
  59 cannot specify whether the frequency is for a tuner or a modulator.
  60
  61 To query and change modulator properties applications use the
  62 :ref:`VIDIOC_G_MODULATOR <VIDIOC_G_MODULATOR>` and
  63 :ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl. Note that
  64 ``VIDIOC_S_MODULATOR`` does not switch the current modulator, when there
  65 is more than one at all. The modulator is solely determined by the
  66 current video output. Drivers must support both ioctls and set the
  67 ``V4L2_CAP_MODULATOR`` flag in the struct
  68 :ref:`v4l2_capability <v4l2-capability>` returned by the
  69 :ref:`VIDIOC_QUERYCAP <VIDIOC_QUERYCAP>` ioctl when the device has
  70 one or more modulators.
  71
  72
  73 Radio Frequency
  74 ===============
  75
  76 To get and set the tuner or modulator radio frequency applications use
  77 the :ref:`VIDIOC_G_FREQUENCY <VIDIOC_G_FREQUENCY>` and
  78 :ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_FREQUENCY>` ioctl which both take
  79 a pointer to a struct :ref:`v4l2_frequency <v4l2-frequency>`. These
  80 ioctls are used for TV and radio devices alike. Drivers must support
  81 both ioctls when the tuner or modulator ioctls are supported, or when
  82 the device is a radio device.
  83
  84
  85 .. ------------------------------------------------------------------------------
  86 .. This file was automatically converted from DocBook-XML with the dbxml
  87 .. library (https://github.com/return42/sphkerneldoc). The origin XML comes
  88 .. from the linux kernel, refer to:
  89 ..
  90 .. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook
  91 .. ------------------------------------------------------------------------------