This is a port of the FlexiHal improvements back to the good'ol GRBLHAL2k board. Switching to a recent grblhal build fixed the modbus communication issues I had where everything stalled.
It's specific to my machine, e.g. if you use another spindle you probably have to edit my_machine.h
Also it uses a more recent grblhal build than the FlexiHal build while writing this readme.