The system fit in two 16KB EPROMS for a total of 32KB, but only one of the 16KB ROMS could be mapped into the address space at a time.
The way this worked was that the compiler was self-hosted (i.e. written in ISO Pascal and compiled itself) and generated our own stack-based virtual machine code which we referred to as BL-code based on our own initials.
One of the 16K ROMS contained the BL-code of the self-compiled compiler... which only fit after a considerable amount of effort, including a few "macro" BL-codes designed for the purpose. Remember this was full BSI-certified ISO-Pascal, plus Acorn extensions for graphics etc, not some toy subset.
The other 16K ROM contained everything else, meaning the BL-code interpreter, screen editor, run-time libraries (floating point - which we copied from BBC basic, Pascal I/O, heap, etc), and command line interpreter. The editor, which I wrote, was around 4KB and fairly sophisticated for the time, including full regex global replace.
One interesting tidbit is how the system actually ran given that the compiler was in one ROM, and the interpreter needed to run it in the other ROM, with only one ROM able to be mapped into the address space at a time... The way we handled this was to relocate the interpreter into RAM in order to run the compiler (but run from ROM when running user programs), so the interpreter was organized into pure code, pure data and relocatable address tables to make this possible.
Getting the whole system to fit into those two 16K ROMS was a heck of a challenge!
Having grown up in Brazil, I never had contact with the BBC micros until I became interested in retro computing. What you folks accomplished is not appreciated enough on the other side of the Atlantic.
I was co-author of Acorn ISO Pascal.
The system fit in two 16KB EPROMS for a total of 32KB, but only one of the 16KB ROMS could be mapped into the address space at a time.
The way this worked was that the compiler was self-hosted (i.e. written in ISO Pascal and compiled itself) and generated our own stack-based virtual machine code which we referred to as BL-code based on our own initials.
One of the 16K ROMS contained the BL-code of the self-compiled compiler... which only fit after a considerable amount of effort, including a few "macro" BL-codes designed for the purpose. Remember this was full BSI-certified ISO-Pascal, plus Acorn extensions for graphics etc, not some toy subset.
The other 16K ROM contained everything else, meaning the BL-code interpreter, screen editor, run-time libraries (floating point - which we copied from BBC basic, Pascal I/O, heap, etc), and command line interpreter. The editor, which I wrote, was around 4KB and fairly sophisticated for the time, including full regex global replace.
One interesting tidbit is how the system actually ran given that the compiler was in one ROM, and the interpreter needed to run it in the other ROM, with only one ROM able to be mapped into the address space at a time... The way we handled this was to relocate the interpreter into RAM in order to run the compiler (but run from ROM when running user programs), so the interpreter was organized into pure code, pure data and relocatable address tables to make this possible.
Getting the whole system to fit into those two 16K ROMS was a heck of a challenge!