Protocol decoder:cec

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cec
HDMI Connector Pinout.svg
Name HDMI-CEC
Description HDMI Consumer Electronics Control (CEC) protocol.
Status supported
License GPLv2+
Source code decoders/cec
Input logic
Output
Probes cec
Optional probes
Options

The cec protocol decoder decodes the Consumer Electronics Control (CEC) protocol, a feature of HDMI designed to allow users to command and control devices connected through HDMI.

Hardware

CEC Bus can be found in pin 13 of the HDMI connector:

HDMI Connector Pinout.svg

Protocol

It is a one-wire, bidirectional, serial bus that is based on the CENELEC standard AV.link protocol to perform remote control functions.

CEC is a separate electrical signal from the other HDMI signals. This allows a device to disable its high-speed HDMI circuitry in sleep mode, but be woken up by CEC. It is a single shared bus, which is directly connected between all HDMI ports on a device, so it can flow through a device which is completely powered off (not just asleep).

The bus is electrically identical to the AV.link protocol, but CEC adds a detailed higher-level message protocol.

The bus is an open-collector line, somewhat like I²C, passively pulled up to +3.3 V, and driven low to transmit a bit.

PulseView screenshots

Usage examples

Print all annotations (very verbose):

 $ sigrok-cli -i data.sr -P cec:CEC=CEC
 cec-1: ST
 cec-1: 0
 cec-1: 0
 cec-1: 1
 cec-1: 1
 cec-1: 0
 cec-1: 0
 cec-1: 0
 cec-1: 0
 cec-1: 0x30
 cec-1: EOM=N
 cec-1: ACK
 cec-1: 0
 cec-1: 0
 cec-1: 0
 cec-1: 0
 cec-1: 0
 cec-1: 1
 cec-1: 0
 cec-1: 0
 cec-1: 0x04
 cec-1: EOM=Y
 cec-1: ACK
 cec-1: 30:04
 cec-1: HDR: Tuner_1, TV | OPC: IMAGE_VIEW_ON | R: ACK

Print frames only:

 $ sigrok-cli -i data.sr -P cec:CEC=CEC -A cec=frames
 cec-1: 30:04
 cec-1: 35
 cec-1: 35
 cec-1: 3f:82:10:00
 cec-1: 30:8f
 cec-1: 03:90:01
 cec-1: 30:44:6d
 cec-1: 35
 cec-1: 35
 cec-1: 30:04
 cec-1: 35
 cec-1: 35
 cec-1: 30:0d
 cec-1: 35
 cec-1: 35
 cec-1: 35
 cec-1: 35
 cec-1: 30:04
 cec-1: 35
 cec-1: 35
 cec-1: 30:8f
 cec-1: 03:90:01
 cec-1: 35
 cec-1: 35
 cec-1: 35
 cec-1: 35
 cec-1: 35
 cec-1: 35
 cec-1: 30:04

Print sections only:

 $ sigrok-cli -i data.sr -P cec:CEC=CEC -A cec=sections
 cec-1: HDR: Tuner_1, TV | OPC: IMAGE_VIEW_ON | R: ACK
 cec-1: HDR: Tuner_1, AudioSystem | OPC: PING | R: NACK
 cec-1: HDR: Tuner_1, AudioSystem | OPC: PING | R: NACK
 cec-1: HDR: Tuner_1, Broadcast | OPC: ACTIVE_SOURCE | OPS: 0x10, 0x00 | R: ACK
 cec-1: HDR: Tuner_1, TV | OPC: GIVE_DEVICE_POWER_STATUS | R: ACK
 cec-1: HDR: TV, Tuner_1 | OPC: REPORT_POWER_STATUS | OPS: 0x01 | R: ACK
 cec-1: HDR: Tuner_1, TV | OPC: USER_CONTROL_PRESSED | OPS: 0x6d | R: ACK
 cec-1: HDR: Tuner_1, AudioSystem | OPC: PING | R: NACK
 cec-1: HDR: Tuner_1, AudioSystem | OPC: PING | R: NACK
 cec-1: HDR: Tuner_1, TV | OPC: IMAGE_VIEW_ON | R: ACK
 cec-1: HDR: Tuner_1, AudioSystem | OPC: PING | R: NACK
 cec-1: HDR: Tuner_1, AudioSystem | OPC: PING | R: NACK
 cec-1: HDR: Tuner_1, TV | OPC: TEXT_VIEW_ON | R: ACK
 cec-1: HDR: Tuner_1, AudioSystem | OPC: PING | R: NACK
 cec-1: HDR: Tuner_1, AudioSystem | OPC: PING | R: NACK
 cec-1: HDR: Tuner_1, AudioSystem | OPC: PING | R: NACK
 cec-1: HDR: Tuner_1, AudioSystem | OPC: PING | R: NACK
 cec-1: HDR: Tuner_1, TV | OPC: IMAGE_VIEW_ON | R: ACK
 cec-1: HDR: Tuner_1, AudioSystem | OPC: PING | R: NACK
 cec-1: HDR: Tuner_1, AudioSystem | OPC: PING | R: NACK
 cec-1: HDR: Tuner_1, TV | OPC: GIVE_DEVICE_POWER_STATUS | R: ACK
 cec-1: HDR: TV, Tuner_1 | OPC: REPORT_POWER_STATUS | OPS: 0x01 | R: ACK
 cec-1: HDR: Tuner_1, AudioSystem | OPC: PING | R: NACK
 cec-1: HDR: Tuner_1, AudioSystem | OPC: PING | R: NACK
 cec-1: HDR: Tuner_1, AudioSystem | OPC: PING | R: NACK
 cec-1: HDR: Tuner_1, AudioSystem | OPC: PING | R: NACK
 cec-1: HDR: Tuner_1, AudioSystem | OPC: PING | R: NACK
 cec-1: HDR: Tuner_1, AudioSystem | OPC: PING | R: NACK
 cec-1: HDR: Tuner_1, TV | OPC: IMAGE_VIEW_ON | R: ACK
 cec-1: HDR: Tuner_1, AudioSystem | OPC: PING | R: NACK
 cec-1: HDR: Tuner_1, AudioSystem | OPC: PING | R: NACK
 cec-1: HDR: Tuner_1, TV | OPC: GIVE_DEVICE_POWER_STATUS | R: ACK
 cec-1: HDR: TV, Tuner_1 | OPC: REPORT_POWER_STATUS | OPS: 0x01 | R: ACK

Current status

The CEC protocol decoder is capable of the following:

  • Decoding all low level parts: START, BITs, EOM, ACK / NACK
  • Resolve names of all logical addresses
  • Resolve names of all opcodes
  • Detect (and warn) timing errors
  • Detect (and warn) misplaced bits, etc.

Not implemented:

  • Operands of the opcodes are not parsed, only printed.