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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>
32 lines
1.4 KiB
ReStructuredText
32 lines
1.4 KiB
ReStructuredText
.. _cec-intro:
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Introduction
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============
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.. note:: This documents the proposed CEC API. This API is not yet finalized
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and is currently only available as a staging kernel module.
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HDMI connectors provide a single pin for use by the Consumer Electronics
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Control protocol. This protocol allows different devices connected by an
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HDMI cable to communicate. The protocol for CEC version 1.4 is defined
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in supplements 1 (CEC) and 2 (HEAC or HDMI Ethernet and Audio Return
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Channel) of the HDMI 1.4a (:ref:`hdmi`) specification and the
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extensions added to CEC version 2.0 are defined in chapter 11 of the
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HDMI 2.0 (:ref:`hdmi2`) specification.
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The bitrate is very slow (effectively no more than 36 bytes per second)
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and is based on the ancient AV.link protocol used in old SCART
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connectors. The protocol closely resembles a crazy Rube Goldberg
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contraption and is an unholy mix of low and high level messages. Some
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messages, especially those part of the HEAC protocol layered on top of
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CEC, need to be handled by the kernel, others can be handled either by
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the kernel or by userspace.
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In addition, CEC can be implemented in HDMI receivers, transmitters and
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in USB devices that have an HDMI input and an HDMI output and that
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control just the CEC pin.
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Drivers that support CEC will create a CEC device node (/dev/cecX) to
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give userspace access to the CEC adapter. The
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:ref:`CEC_ADAP_G_CAPS` ioctl will tell userspace what it is allowed to do.
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