Sorry I meant to answer this topic when Ed prompted me but it slipped my mind.
You shouldn't need all of those COP calls to be implemented - I think the BBC Micro build and shim only do a handful
There's documentation of most of the Communictor OS here
https://github.com/dominicbeesley/Commu ... e/main/doc and that git contains my disassembly of the Communicator's OS which has a many of the calls documented too. There's a html version here
https://raw.githack.com/dominicbeesley/ ... LLK-COP_00 other modules of the OS are available in the git repository.
It has been a while since I looked at this but I think possibly the way to proceed would be to go with bas816new.asm file and go through and copy the IFDEF MOS sections and make new IFDEF GREGORIO sections
Then you'll need to set up the BASIC environment by making a customised init sequence (around line 767) where you setup a private direct page for BASIC and set up the memory location and size that BASIC uses to store its program.
A minimal first boot of BASIC will probably need simple implementations of OSRDCH, OSWORD (0) - read a line, OSWRCH/OSASCI to write a character. You could start by implementing the communicator COP calls but they are complicated with a load of stuff for setting up multi-tasking.
D