I've been trying to learn more about the AppleNet networking cards by peering at ROM disassemblies. There are two to choose from: the boot ROM that tells the Lisa how to boot from AppleNet, and the Z8 ROM for the AppleNet card's MCU. It's likely that a full understanding will require a careful analysis of both,* but I know 68k assembly best
So, I've had a good look through the boot ROM, and while I hardly understand everything, I may have found enough organisation for other people to delve if they're feeling curious. My commentary is here, alongside some reverse-engineered schematics I'd derived earlier:
https://github.com/stepleton/applenet/blob/master/applenet_boot_rom.txtThere are plenty of mysteries, including why the boot program overwrites $110 (the place where the Lisa's own boot ROM stores a pointer to the bitmap display RAM) and, well, anything at all about what the routine at disassembly address $3B2 is doing.
Have a look if you like a puzzle. If it's of interest, Bitsavers has the
Z8 ROM disassembly as well, albeit without commentary---I've only begun looking at this code and know very little.
(Oh, and: the thread title says "attempts" --- I'd imagined that discussions of the Z8 disassembly might appear here too someday.)
* An additional item to disentangle is the PAL chip---the equations for it live
on Bitsavers, but it's a bit too hard for me to understand on its own. It'll probably be useful to interpret what it does from the point of view of the Z8, which manipulates some of its inputs.
