Does anybody know what changes need to be done on the firmware for OpenEVSE to work on the ATMEGA 644 chip instead of an ATMEGA 328?
You will have to put the 2 processor data sheets side by side and see if all the needed hardware from the 328 is also available on the 644 and then update the firmware for the differences.
If you wish to run OpenEVSE using an ATMEGA 644 chip instead of an ATMEGA 328 chip, some modifications must be made to its firmware code in order to accommodate these differences in memory and pin count between both chips. You'll have to update pin assignments, memory usage and references specific to an ATMEGA 328 as they differ; though this process might seem daunting at first, don't give up; double-check all pin configurations before moving forward!
thanks and regards