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author | Mauro Carvalho Chehab <mchehab@s-opensource.com> | 2016-07-08 11:40:06 -0300 |
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committer | Mauro Carvalho Chehab <mchehab@s-opensource.com> | 2016-07-08 11:59:40 -0300 |
commit | 60c2820d0f6d3497975b6488e2599f8f611d8b95 (patch) | |
tree | b3b03707c6438ea9b99cc57e847ebf517f968ab1 /Documentation/media/uapi/v4l/tuner.rst | |
parent | a97369b5e21ea9b8b5fef7c0f4f48bbe60c07ca3 (diff) | |
download | linux-60c2820d0f6d3497975b6488e2599f8f611d8b95.tar.bz2 |
doc_rst: rename the media Sphinx suff to Documentation/media
The name of the subsystem is "media", and not "linux_tv". Also,
as we plan to add other stuff there in the future, let's
rename also the media uAPI book to media_uapi, to make it
clearer.
No functional changes.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Diffstat (limited to 'Documentation/media/uapi/v4l/tuner.rst')
-rw-r--r-- | Documentation/media/uapi/v4l/tuner.rst | 82 |
1 files changed, 82 insertions, 0 deletions
diff --git a/Documentation/media/uapi/v4l/tuner.rst b/Documentation/media/uapi/v4l/tuner.rst new file mode 100644 index 000000000000..23d0e00aefdd --- /dev/null +++ b/Documentation/media/uapi/v4l/tuner.rst @@ -0,0 +1,82 @@ +.. -*- coding: utf-8; mode: rst -*- + +.. _tuner: + +********************* +Tuners and Modulators +********************* + + +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`` +field of the respective struct :ref:`v4l2_input <v4l2-input>` +returned by the :ref:`VIDIOC_ENUMINPUT` ioctl is +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 +:ref:`VIDIOC_G_TUNER <VIDIOC_G_TUNER>` and +:ref:`VIDIOC_S_TUNER <VIDIOC_G_TUNER>` ioctls, respectively. The +struct :ref:`v4l2_tuner <v4l2-tuner>` returned by :ref:`VIDIOC_G_TUNER <VIDIOC_G_TUNER>` +also contains signal status information applicable when the tuner of the +current video or radio input is queried. Note that :ref:`VIDIOC_S_TUNER <VIDIOC_G_TUNER>` +does not switch the 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 and set the ``V4L2_CAP_TUNER`` flag in the struct +:ref:`v4l2_capability <v4l2-capability>` returned by the +:ref:`VIDIOC_QUERYCAP` ioctl when the device has +one or more tuners. + + +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 +:ref:`v4l2_output <v4l2-output>` returned by the +:ref:`VIDIOC_ENUMOUTPUT` ioctl is set to +``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 +:ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_FREQUENCY>` ioctl where you +cannot specify whether the frequency is for a tuner or a modulator. + +To query and change modulator properties applications use the +:ref:`VIDIOC_G_MODULATOR <VIDIOC_G_MODULATOR>` and +:ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl. Note that +:ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` does not switch the current modulator, when there +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 +:ref:`v4l2_capability <v4l2-capability>` returned by the +:ref:`VIDIOC_QUERYCAP` ioctl when the device has +one or more modulators. + + +Radio Frequency +=============== + +To get and set the tuner or modulator radio frequency applications use +the :ref:`VIDIOC_G_FREQUENCY <VIDIOC_G_FREQUENCY>` and +:ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_FREQUENCY>` ioctl which both take +a pointer to a struct :ref:`v4l2_frequency <v4l2-frequency>`. These +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. |