Complete and useful CPUs can work without registers as part of the machine instructions. Once instance is the Zylin CPU core, which is a tiny 32-bit processor designed to be synthesized into FPGAs with complete support by the GCC compiler. It's stack based.

A nice overview is given here: http ...

Okay, tinyload is now 962 bytes. I think that's enough to not reach into the the I/O region starting at 0xffd0. So a 63K RAM + 1K ROM configuration is possible for the MULTICOMP.

Okay, am now down to 1019 bytes and I can quite possibly chew off some additional bytes. If I manage to get it small enough to clear the I/O-area (which overlaps ROM on MULTICOMP) and the reset/irq vectors one can squeeze it into a 1K ROM, making 63K of RAM available.

As for preloading into RAM ...

I forked a new code base for the "small bootloader with FAT-support" idea, called "tinyload". The source is over at https://github.com/maikmerten/tinyload

I'm currently down to 1237 bytes, so 2K of ROM indeed is plenty. I'm sure I can shave off even more, but getting this into 1K may prove ...

Thanks for your kind comment! I hesitate to call it a "real system", but at least it makes getting software to the MULTICOMP a bit easier ;)

I noticed I did no attach a binary for easy experimentation, so here's a random up-to-date version.

The code currently occupies approximately 4K (of the 8K ...

Hello there,

some time ago I stumbled over Grant Searle's MULTICOMP pick-and-mix FPGA computer over at http://searle.hostei.com/grant/Multicomp/

My favorite flavor is the 6502 version (having had some previous adventures with C64 programming). By default MULTICOMP has a Microsoft Basic in ROM ...