Apparently, CEC-wiring is mandatory in HDMI but product implementation voluntary.
According to Wikipedia different trade names for the IMPLEMENTED CEC are:
Anynet (Samsung); Aquos Link (Sharp); BRAVIA Sync (Sony); HDMI-CEC (Hitachi); Kuro Link (Pioneer); CE-Link and Regza Link (Toshiba); RIHD (Remote Interactive over HDMI) (Onkyo); SimpLink (LG); HDAVI Control, EZ-Sync, VIERA Link (Panasonic); EasyLink (Philips); and NetCommand for HDMI (Mitsubishi).Source: http://en.wikipedia.org/wiki/HDMI#CEC
The specification is built on AV.Link, which is used in SCART.
You can download the HDMI 1.3a specification for free by filling in the form here: http://www.hdmi.org/manufacturer/specification.aspx
It exists a HDMI-CEC to USB and RS-232 bridge/converter
as featured on Hackaday
. This guy Valkyriemt made it work for him: Controlling Volume… Look Ma, no extra Wires!
A white paper on what this device does and how to use it can be downloaded here: PDF
Rainshadowtech.com which makes the device writes:
(HDMI-CEC to USB and RS-232 converter) device has been demonstrated to work with TVs from Samsung, Sharp, Sony, Toshiba, LG, Panasonic, and Mitsubishi. TV CEC capabilities vary widely. Many recent models can be powered on, off, and have the external HDMI input source chosen via CEC.
This device could be connected into the HDMI cable between the TV and the PC, but that is not necessary. Because the CEC bus is a single wire bus between all components, the device can be plugged into any HDMI input in the Home Theater system. The advantage of this approach is that the integrity of the cable (and therefore the quality of the signal) between the TV and the PC does not need to compromised by adding this device to it.
As far as I understand it having merely looked at the HDMI specs, the specification allows for pass-thru signalling; meaning one sleeping device will still pass through messages (such as SHUT DOWN) to other connected devices that are on or off. In other words, HDMI cables can become an extension of the network cabling for LinuxMCE to talk to devices directly the last-three-feet.
I personally have a Toshiba REGZA 42" (42XV550P) Television that I bought a couple of years back, and it doesn't have a serial RS232 controller. It does have 3 HDMI connectors though. I am not much of an electronics guy either, but I think we should be able to wing it.
The remote control for my Toshiba REGZA 42" has its own REGZA Link mode, which is Toshiba's implementation of HDMI's CEC, though sending them using IR. Showcase: http://www.regza-asia.com/technology/technology_regzalink.asp?cat=sc4
If I can record the IR signals sent to the television in REGZA Link mode, I should be able to send the same signals from a computer to the television (and other CEC devices), given I have a way to interface with HDMI with on the command-line and a HDMI controller on the computer. From this it should be possible to create a device template or "device class template" (e.g. REGZA-device), no?
The CEC specification has its own addressing scheme (think DHCP) with logical addresses 4, 8 and 11 reserved for playback devices.
The CEC wiring IS MANDATORY so you would not need more than one HDMI cable between computer and television, since the wiring for the CEC signalling is already inside the cable (in other words, HDMI cables send CEC along with VIDEO and AUDIO). But I don't know exactly what tty you could use (if any).. Just some thoughts on the matter..