Protocol decoder:cec
 | |
| 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:
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
Ping (poll) frames
Vendor command frame
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.