This is a Consumer Electronics Control (CEC) implementation for LG TVs that lack CEC support. It's meant to run on an Atmel ATtiny-45 AVR. The code includes support for decoding IR commands from an NEC protocol remote, sending and receiving commands to the TV via the RS-232 management port, and sending and receiving CEC commands.
The code is currently somewhat customized for a single given configuration, the one I have. Some limitations are that it passes through all remote keys except power, mute, and volume up/down to the current CEC device rather than to the TV. Additionally, the firmware only supports inputs that identify as CEC devices.
The IR interface is compatible with the NEC IR protocol:
http://www.sbprojects.com/knowledge/ir/nec.php
Support is implemented via as assembly interrupt service routine. An IR decoder should be connected to INT0. The handler uses the jiffies value generated by the UART code.
LG TVs have a 9600 baud management port. This port can be used to get TV status, send remote control codes, and send commands. Because the firmware must also implement CEC and IR support, UART support is offloaded to the USI hardware. USI runs at 4 times the serial rate which allows the receive side to properly align with the incoming asyncrounous signal. This allows up to 4 serial bit times between interrupt handler routines.
CEC support is provided by the AVR-CEC library using the PWM transmit mode and the software receive mode. The firmware sends appropriate keys (PLAY, PAUSE, etc) as deck control commands and all others as CEC UI commands according to a keymap stored in the EEPROM. The internal CEC logic supports one touch play (remote device turns on TV and selects input), choosing a new source when an inactive source message is received, processing routing changes, and responding to active source messages.
Sending a 16 byte vendor command with the final byte as 0xb1 causes the firmware to enter bootloader mode. In this mode new firmware can be programmed over the CEC bus via the cec_flash.py script.
A keymap between LG TV remote keys and CEC UI key codes is stored in the EEPROM. Reflashing of the EEPROM can either be done through the programming pins or via a special hexfile that embeds the keymap and programs it. After running this hexfile, the device re-enters bootloader mode and the original hexfile must be reloaded.