In the end it took quite some hacking, but the result is nice enough: I can play
Zork on an AVR!
It's... not really quick, though. The time from bootup to where I took this screenshot is about 30 seconds. Ofcourse, stuff like memory and SD-card-access could be optimized a bit more by e.g. adding a bit of cache, but I'll never get the same speed as the original: the AVR is just too slow to handle the realtime emulation needed, just as expected.
The emulation isn't completely 100% either: some programs tend to crash or act up, most of the Z80-specific instructions aren't emulated yet and the BIOS still bugs now and then. I was actually thinking of solving these problems and including more functionality like an integrated VGA-out and keyboard in, and maybe using disk-images instead of raw SD-cards... but then I stepped back and remembered I was writing a proof-of-concept emulator for a system that's already emulated a hundred times better and faster on a random PC.
Anyway, in case you want to build this curiosity by yourself or just want to see the sources: as usual, it's all licensed under the GPLv3 and downloadable here. I'd, as always, appreciate a message or email if you actually manage to do something useful with them.