c7169ad561
Add DocBook documentation for the CEC API. Signed-off-by: Hans Verkuil <hansverk@cisco.com> [k.debski@samsung.com: add documentation for passthrough mode] [k.debski@samsung.com: minor fixes and change of reserved field sizes] Signed-off-by: Kamil Debski <kamil@wypas.org> Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
76 lines
2.7 KiB
XML
76 lines
2.7 KiB
XML
<partinfo>
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<authorgroup>
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<author>
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<firstname>Hans</firstname>
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<surname>Verkuil</surname>
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<affiliation><address><email>hans.verkuil@cisco.com</email></address></affiliation>
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<contrib>Initial version.</contrib>
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</author>
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</authorgroup>
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<copyright>
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<year>2016</year>
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<holder>Hans Verkuil</holder>
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</copyright>
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<revhistory>
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<!-- Put document revisions here, newest first. -->
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<revision>
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<revnumber>1.0.0</revnumber>
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<date>2016-03-17</date>
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<authorinitials>hv</authorinitials>
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<revremark>Initial revision</revremark>
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</revision>
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</revhistory>
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</partinfo>
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<title>CEC API</title>
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<chapter id="cec-api">
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<title>CEC: Consumer Electronics Control</title>
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<section id="cec-intro">
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<title>Introduction</title>
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<para>
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Note: this documents the proposed CEC API. This API is not yet finalized and
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is currently only available as a staging kernel module.
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</para>
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<para>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 HDMI cable
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to communicate. The protocol for CEC version 1.4 is defined in supplements 1 (CEC)
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and 2 (HEAC or HDMI Ethernet and Audio Return Channel) of the HDMI 1.4a
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(<xref linkend="hdmi" />) specification and the extensions added to CEC version 2.0
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are defined in chapter 11 of the HDMI 2.0 (<xref linkend="hdmi2" />) specification.
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</para>
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<para>The bitrate is very slow (effectively no more than 36 bytes per second) and
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is based on the ancient AV.link protocol used in old SCART connectors. The protocol
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closely resembles a crazy Rube Goldberg contraption and is an unholy mix of low and
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high level messages. Some messages, especially those part of the HEAC protocol layered
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on top of CEC, need to be handled by the kernel, others can be handled either by the
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kernel or by userspace.</para>
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<para>In addition, CEC can be implemented in HDMI receivers, transmitters and in USB
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devices that have an HDMI input and an HDMI output and that control just the CEC pin.</para>
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<para>Drivers that support CEC will create a CEC device node (/dev/cecX)
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to give userspace access to the CEC adapter. The &CEC-ADAP-G-CAPS; ioctl will tell userspace
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what it is allowed to do.</para>
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</section>
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</chapter>
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<appendix id="cec-user-func">
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<title>Function Reference</title>
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<!-- Keep this alphabetically sorted. -->
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&sub-cec-func-open;
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&sub-cec-func-close;
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&sub-cec-func-ioctl;
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&sub-cec-func-poll;
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<!-- All ioctls go here. -->
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&sub-cec-ioc-adap-g-caps;
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&sub-cec-ioc-adap-g-log-addrs;
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&sub-cec-ioc-adap-g-phys-addr;
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&sub-cec-ioc-dqevent;
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&sub-cec-ioc-g-mode;
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&sub-cec-ioc-receive;
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</appendix>
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