summaryrefslogtreecommitdiff
path: root/Documentation/userspace-api/media/cec/cec-intro.rst
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/userspace-api/media/cec/cec-intro.rst')
-rw-r--r--Documentation/userspace-api/media/cec/cec-intro.rst49
1 files changed, 49 insertions, 0 deletions
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 000000000000..a4db82388202
--- /dev/null
+++ b/Documentation/userspace-api/media/cec/cec-intro.rst
@@ -0,0 +1,49 @@
+.. 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.