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.. -*- coding: utf-8; mode: rst -*-
.. _tuner:
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Tuners and Modulators
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Tuners
======
Video input devices can have one or more tuners demodulating a RF
signal. Each tuner is associated with one or more video inputs,
depending on the number of RF connectors on the tuner. The `` type ``
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field of the respective struct :c:type: `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
index number of the tuner.
Radio input devices have exactly one tuner with index zero, no video
inputs.
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 :c:type: `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
determined by the current video input. Drivers must support both ioctls
[media] docs-rst: fix cross-references for videodev2.h
There are several broken references there, due to the conversion to
C domain. Fix them using this shell script and manually adjust what's
broken:
# funcs is a file with the broken functions/references
for i in $(cat funcs|sort|uniq|perl -ne 'print "$1\n" if (m/(\S+)$/)'); do
i=${i//-/_}
echo $i
j=${i//_/-}
for k in $(git grep -l "_$j:" Documentation/); do
sed s,\_$j\:,"c\:type\:\: $i", <$k >a && mv a $k
done
for k in $(git grep -l "$j" Documentation/media/*.exceptions); do
sed s,$j,":c\:type\:\`$i\`", <$k >a && mv a $k
done
for k in $(git grep -l "$j" Documentation/); do
sed "s,:ref:\`$i <$j>\`,:c:type:\`$i\`," <$k >a && mv a $k
sed "s,:ref:\`$j\`,:c:type:\`$i\`," <$k >a && mv a $k
sed -E "s,:ref:\`(.*)<$j>\`,:c:type:\`\1<$i>\`," <$k >a && mv a $k
done
for k in $(git grep -l "<$j>" include/media); do
sed -E "s,:ref:\`(.*)<$j>\`,enum \&$i," <$k >a && mv a $k
done
done
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
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and set the `` V4L2_CAP_TUNER `` flag in the struct :c:type: `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
==========
Video output devices can have one or more modulators, uh, modulating a
video signal for radiation or connection to the antenna input of a TV
set or video recorder. Each modulator is associated with one or more
video outputs, depending on the number of RF connectors on the
modulator. The `` type `` field of the respective struct
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:c:type: `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
index number of the modulator.
Radio output devices have exactly one modulator with index zero, no
video outputs.
A video or radio device cannot support both a tuner and a modulator. Two
separate device nodes will have to be used for such hardware, one that
supports the tuner functionality and one that supports the modulator
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.
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
current video output. Drivers must support both ioctls and set the
`` V4L2_CAP_MODULATOR `` flag in the struct
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:c:type: `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.
Radio Frequency
===============
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 :c:type: `v4l2_frequency` . These
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ioctls are used for TV and radio devices alike. Drivers must support
both ioctls when the tuner or modulator ioctls are supported, or when
the device is a radio device.
