diff options
Diffstat (limited to 'Documentation/media/uapi/cec/cec-intro.rst')
| -rw-r--r-- | Documentation/media/uapi/cec/cec-intro.rst | 31 |
1 files changed, 31 insertions, 0 deletions
diff --git a/Documentation/media/uapi/cec/cec-intro.rst b/Documentation/media/uapi/cec/cec-intro.rst new file mode 100644 index 000000000000..d6a878866b3f --- /dev/null +++ b/Documentation/media/uapi/cec/cec-intro.rst @@ -0,0 +1,31 @@ +.. _cec-intro: + +Introduction +============ + +Note: this documents the proposed CEC API. This API is not yet finalized +and is currently only available as a staging kernel module. + +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. |