I've been coding 6502-assembler for a while now, working on the system code. It's interesting to plan all the bits, and see how it works out in reality. So far so good.
Latest functionality I made was an S19-loader so it is easier to start new threads without juggling with the SD-card. The S19 format is surprisingly powerful, but can also be implemented VERY compactly if corners are cut. I'll have to revisit this in the future, to add the corners.
Focus now is on making os-code to be able to load/start/stop/manipulate threads. I've decided the commands for this will be available from Basic, bringing a truly 80's retro vibe. It's also quite usable. Beginnings of re-entrant os routines have been coded, but are not fully tested.
Basic will run as thread 0 and it will be possible to run more threads. Only zero page memory and cpu-cycles are limiting the number of practically usable threads.
In a weak moment I was thinking about trying out cc65 to write code in C. That idea is postponed since I started this project to code 6502 assembler.