From 2c3c1048746a4622d8c89a29670120dc8fab93c4 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sun, 7 Apr 2024 20:49:45 +0200 Subject: Adding upstream version 6.1.76. Signed-off-by: Daniel Baumann --- .../userspace-api/media/cec/cec-intro.rst | 42 ++++++++++++++++++++++ 1 file changed, 42 insertions(+) create mode 100644 Documentation/userspace-api/media/cec/cec-intro.rst (limited to 'Documentation/userspace-api/media/cec/cec-intro.rst') diff --git a/Documentation/userspace-api/media/cec/cec-intro.rst b/Documentation/userspace-api/media/cec/cec-intro.rst new file mode 100644 index 000000000..1884ea090 --- /dev/null +++ b/Documentation/userspace-api/media/cec/cec-intro.rst @@ -0,0 +1,42 @@ +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later + +.. _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 `_ 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. -- cgit v1.2.3