I’ve done this sort of backwards. I’m now looking at Ben Eater’s fantastic 6502 videos, after having built my own Planck SBC. In one of them, Ben discusses how to port Wozmon, the legendary Apple-I machine monitor written by Steve Jobs, to Eater’s 6502 computer. I decided to adapt it to run on the Planck and it’s been a great introduction to ca65, ld65, assembly, and a bunch of other topics, like ACIA delay timings, etc.
Anyway, I now have a working Wozmon monitor for the Planck, along with a couple of primitive build files. I have not yet been able to fit it into 255 bytes, like Ben’s or like the original Wozmon. Going all the way back to basics with burning new ROMs with just the absolute minimum software to get the computer to run has been a really excellent learning experience for me.
Thanks again for creating the Planck single board computer.