Need some advice on threading on a Z80

[brucehoult]

I don't know why it should be impossible. Adding external MMU was common on all such CPUs, even if only for bank switching (but it's the same thing). Preventing access to some banks is not hard. The only hard thing is being able to recover from an illegal access, make it legal, and continue the program. Some early 68000 machines with MMU had two chips with one running a couple of clock cycles behind the other so it could be halted before hitting the exception the first CPU hit.

[RoGeorge]

If you're envisioning some kind of memory protection, you can watch this:
video
(although the title is a bit "catchy", you may find a couple ideas in this.)

That video was discussed 2 years ago in another topic, it's a clickbait, and no Z80 feature discovery.

My conclusion from the other thread, after watching the video back in 2022:

Not a clickbait title, it's a lying title.

To spare others' time, no Z80 secret feature was discovered.  He wants to emulate protected mode in software, after adding some external hardware, then starts to fantasize about generic advantages of protected mode as if Z80 would have such a mode, except Z80 doesn't have any hidden protected mode feature.