Re: Kernel uses only half of Mac IIci memory with built-in video
On Tue, 23 Mar 2021, Brad Boyer wrote:
> On Tue, Mar 23, 2021 at 06:50:05PM +1100, Finn Thain wrote:
> > Anyway, surely this test for CPU_68020 in Source/mmu_support.c in
> > Penguin is bogus. This must have to do with some quirk of the Mac II
> > logic board and not the type of MMU or CPU.
> >
> > So, why sort chunks by address on Mac II? Beats me. I guess I'll have
> > to dig out my Mac II and try EMILE, which doesn't have that hack.
>
> Apparently there was a bug in the original Mac II ROM that couldn't
> handle more than 4MB in bank A. That would mean that anyone who had more
> than 8MB had the larger modules in bank B.
Right. And, of course, the original Mac II is not the only model where
bank B might be larger than bank A.
Also, I found that it's not just the IIsi that has a small bank A that's
all soldered-in. The IIvi/vx and Quadra 700 are in the same category.
It appears that both Penguin and EMILE are likely to disappoint on these
systems.
It's a pity bootloaders don't share more code. I think there's a good
argument for fixing this in EMILE and then wrapping a MacOS GUI around it,
that could supercede Penguin eventually.
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