Code for an ATTINY4313 to operate a motorized volume potentiometer in response
to HDMI CEC volume commands sent from a TV.  It might be useful as a reference
for someone implementing the CEC protocol on an AVR.

This was part of a project to add remote volume control to a Pioneer SX-950
receiver.  The project is described in more detail at
https://blog.ldtlb.com/2020/10/14/pioneer-sx950-hdmi-cec-volume.html

See schematic.svg for the hardware configuration.

It has only been tested with an LG OLED65B6P.