706f8a9975
There are several notes and warning mesages in the middle of the media docbook. Use the ReST tags for that, as it makes them visually better and hightlights them. While here, modify a few ones to make them clearer. Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
84 lines
3.4 KiB
ReStructuredText
84 lines
3.4 KiB
ReStructuredText
.. -*- coding: utf-8; mode: rst -*-
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.. _tuner:
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*********************
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Tuners and Modulators
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*********************
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Tuners
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======
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Video input devices can have one or more tuners demodulating a RF
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signal. Each tuner is associated with one or more video inputs,
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depending on the number of RF connectors on the tuner. The ``type``
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field of the respective struct :ref:`v4l2_input <v4l2-input>`
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returned by the :ref:`VIDIOC_ENUMINPUT` ioctl is
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set to ``V4L2_INPUT_TYPE_TUNER`` and its ``tuner`` field contains the
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index number of the tuner.
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Radio input devices have exactly one tuner with index zero, no video
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inputs.
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To query and change tuner properties applications use the
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:ref:`VIDIOC_G_TUNER <VIDIOC_G_TUNER>` and
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:ref:`VIDIOC_S_TUNER <VIDIOC_G_TUNER>` ioctls, respectively. The
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struct :ref:`v4l2_tuner <v4l2-tuner>` returned by :ref:`VIDIOC_G_TUNER <VIDIOC_G_TUNER>`
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also contains signal status information applicable when the tuner of the
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current video or radio input is queried.
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.. note:: :ref:`VIDIOC_S_TUNER <VIDIOC_G_TUNER>` does not switch the
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current tuner, when there is more than one at all. The tuner is solely
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determined by the current video input. Drivers must support both ioctls
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and set the ``V4L2_CAP_TUNER`` flag in the struct :ref:`v4l2_capability
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<v4l2-capability>` returned by the :ref:`VIDIOC_QUERYCAP` ioctl when the
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device has one or more tuners.
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Modulators
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==========
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Video output devices can have one or more modulators, uh, modulating a
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video signal for radiation or connection to the antenna input of a TV
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set or video recorder. Each modulator is associated with one or more
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video outputs, depending on the number of RF connectors on the
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modulator. The ``type`` field of the respective struct
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:ref:`v4l2_output <v4l2-output>` returned by the
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:ref:`VIDIOC_ENUMOUTPUT` ioctl is set to
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``V4L2_OUTPUT_TYPE_MODULATOR`` and its ``modulator`` field contains the
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index number of the modulator.
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Radio output devices have exactly one modulator with index zero, no
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video outputs.
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A video or radio device cannot support both a tuner and a modulator. Two
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separate device nodes will have to be used for such hardware, one that
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supports the tuner functionality and one that supports the modulator
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functionality. The reason is a limitation with the
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:ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_FREQUENCY>` ioctl where you
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cannot specify whether the frequency is for a tuner or a modulator.
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To query and change modulator properties applications use the
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:ref:`VIDIOC_G_MODULATOR <VIDIOC_G_MODULATOR>` and
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:ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl. Note that
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:ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` does not switch the current modulator, when there
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is more than one at all. The modulator is solely determined by the
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current video output. Drivers must support both ioctls and set the
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``V4L2_CAP_MODULATOR`` flag in the struct
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:ref:`v4l2_capability <v4l2-capability>` returned by the
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:ref:`VIDIOC_QUERYCAP` ioctl when the device has
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one or more modulators.
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Radio Frequency
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===============
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To get and set the tuner or modulator radio frequency applications use
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the :ref:`VIDIOC_G_FREQUENCY <VIDIOC_G_FREQUENCY>` and
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:ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_FREQUENCY>` ioctl which both take
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a pointer to a struct :ref:`v4l2_frequency <v4l2-frequency>`. These
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ioctls are used for TV and radio devices alike. Drivers must support
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both ioctls when the tuner or modulator ioctls are supported, or when
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the device is a radio device.
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