Z80 protected mode? | MSX Resource Center (Page 1/3)

Par ro

Scribe (4964)

17-10-2022, 10:20

yeah, i saw that clickbait vid last week. next

Par gdx

Enlighted (6219)

17-10-2022, 10:38

This should be useful for SymbOS, but it needs hardware modification is not?

Par geijoenr

Champion (366)

17-10-2022, 10:47

yeah, somewhat click bait. But interesting how easy is to have some sort of protected mode with very little hardware additions.

Also nice that the guy talks about MSX.

Par msd

Paragon (1515)

17-10-2022, 13:24

I think also the cpu overhead of this ‘solution’ has to be taken into account . Having an interrupt for every out/in, then running some code from NMI can have some serious performance impact .

Par DamnedAngel

Champion (266)

17-10-2022, 15:34

Additionally, the suggested architecture for pretecting memory could protect memory mappers (since the management is I/O based), but completely fails protecting MSX SLOTs.
The guy had an epiphany on how to implement protected systems based on 8-bit CPUs, but it would only apply to a new system made with that purpose. For our old architectures it is just useless.

Par Danjovic

Champion (336)

17-10-2022, 17:51

Yeah I agree, the content of the video is cool, but protected mode is not a feature of the CPU itself, like for example the embedded memory refresh controller and the ghost register set (invoked by exx/ ex af,af').
But hey, at 01:31 one the computers shown is a SHARP Hotbit HB-8000 and that alone already earned my LIKE!

Par Briqunullus

Paladin (675)

17-10-2022, 20:26

Too bad he hasn't built an actual system yet, so we can judge its feasibility. But I like his outside-of-the-box thinking. As a concept, it may even excite me more than MSX3, which seems so disconnected from existing hardware.

Par Manuel

Ascended (19469)

17-10-2022, 20:53

ro wrote:

yeah, i saw that clickbait vid last week. next

He actually admits the click bait title in the video very explicitly

Par geijoenr

Champion (366)

17-10-2022, 21:02

It seems this can be done without hardware modifications and in a cartridge _except_ for the NMI input to the CPU?

Par PingPong

Enlighted (4140)

17-10-2022, 23:05

msd wrote:

I think also the cpu overhead of this ‘solution’ has to be taken into account . Having an interrupt for every out/in, then running some code from NMI can have some serious performance impact .

one of the reasons that justify the absesce of a protected mode is that those early processors have too little horse power to efficiently support multitasking even if sybos proved that that can be done.