Documentation/userspace-api/media/cec/cec-intro.rst - linux - Git at Google

 .. Permission is granted to copy, distribute and/or modify this
 .. document under the terms of the GNU Free Documentation License,
 .. Version 1.1 or any later version published by the Free Software
 .. Foundation, with no Invariant Sections, no Front-Cover Texts
 .. and no Back-Cover Texts. A copy of the license is included at
 .. Documentation/userspace-api/media/fdl-appendix.rst.
 ..
 .. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections

 .. _cec-intro:

 Introduction
 ============

 HDMI connectors provide a single pin for use by the Consumer Electronics
 Control protocol. This protocol allows different devices connected by an
 HDMI cable to communicate. The protocol for CEC version 1.4 is defined
 in supplements 1 (CEC) and 2 (HEAC or HDMI Ethernet and Audio Return
 Channel) of the HDMI 1.4a (:ref:`hdmi`) specification and the
 extensions added to CEC version 2.0 are defined in chapter 11 of the
 HDMI 2.0 (:ref:`hdmi2`) specification.

 The bitrate is very slow (effectively no more than 36 bytes per second)
 and is based on the ancient AV.link protocol used in old SCART
 connectors. The protocol closely resembles a crazy Rube Goldberg
 contraption and is an unholy mix of low and high level messages. Some
 messages, especially those part of the HEAC protocol layered on top of
 CEC, need to be handled by the kernel, others can be handled either by
 the kernel or by userspace.

 In addition, CEC can be implemented in HDMI receivers, transmitters and
 in USB devices that have an HDMI input and an HDMI output and that
 control just the CEC pin.

 Drivers that support CEC will create a CEC device node (/dev/cecX) to
 give userspace access to the CEC adapter. The
 :ref:`CEC_ADAP_G_CAPS` ioctl will tell userspace what it is allowed to do.

 In order to check the support and test it, it is suggested to download
 the `v4l-utils <https://git.linuxtv.org/v4l-utils.git/>`_ package. It
 provides three tools to handle CEC:

 - cec-ctl: the Swiss army knife of CEC. Allows you to configure, transmit
   and monitor CEC messages.

 - cec-compliance: does a CEC compliance test of a remote CEC device to
   determine how compliant the CEC implementation is.

 - cec-follower: emulates a CEC follower.
	.. Permission is granted to copy, distribute and/or modify this
	.. document under the terms of the GNU Free Documentation License,
	.. Version 1.1 or any later version published by the Free Software
	.. Foundation, with no Invariant Sections, no Front-Cover Texts
	.. and no Back-Cover Texts. A copy of the license is included at
	.. Documentation/userspace-api/media/fdl-appendix.rst.
	..
	.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections

	.. _cec-intro:

	Introduction
	============

	HDMI connectors provide a single pin for use by the Consumer Electronics
	Control protocol. This protocol allows different devices connected by an
	HDMI cable to communicate. The protocol for CEC version 1.4 is defined
	in supplements 1 (CEC) and 2 (HEAC or HDMI Ethernet and Audio Return
	Channel) of the HDMI 1.4a (:ref:`hdmi`) specification and the
	extensions added to CEC version 2.0 are defined in chapter 11 of the
	HDMI 2.0 (:ref:`hdmi2`) specification.

	The bitrate is very slow (effectively no more than 36 bytes per second)
	and is based on the ancient AV.link protocol used in old SCART
	connectors. The protocol closely resembles a crazy Rube Goldberg
	contraption and is an unholy mix of low and high level messages. Some
	messages, especially those part of the HEAC protocol layered on top of
	CEC, need to be handled by the kernel, others can be handled either by
	the kernel or by userspace.

	In addition, CEC can be implemented in HDMI receivers, transmitters and
	in USB devices that have an HDMI input and an HDMI output and that
	control just the CEC pin.

	Drivers that support CEC will create a CEC device node (/dev/cecX) to
	give userspace access to the CEC adapter. The
	:ref:`CEC_ADAP_G_CAPS` ioctl will tell userspace what it is allowed to do.

	In order to check the support and test it, it is suggested to download
	the `v4l-utils <https://git.linuxtv.org/v4l-utils.git/>`_ package. It
	provides three tools to handle CEC:

	- cec-ctl: the Swiss army knife of CEC. Allows you to configure, transmit
	and monitor CEC messages.

	- cec-compliance: does a CEC compliance test of a remote CEC device to
	determine how compliant the CEC implementation is.

	- cec-follower: emulates a CEC follower.