[B2-devel] Macintosh memory information?

[Alexander v. G. <kal...@un...>]

Does anyone have any documentation on the memory layout of the old world 
Macintosh? (Performa 6400 era)

I've been looking to rework how SheepShear manages memory and it's not 
completely clear to me how it does
it's memory translation.  Most of the bugs I've seen on x86_64 are due to 
the exact memory mapping on emulated
powerpc systems (eg, hard coded memory addresses we *have* to map for things 
to function) and something getting mangled
on x86_64.
https://github.com/kallisti5/sheepshear/issues/15#issuecomment-7045089

I see memory maps for the really early Mac's, but am failing to find 
anything for the later old world machines
online or in the old Macintosh service manuals.

Here is what I know for a fact looking at the code:

Low memory area, - 0x0        - 0x3000  (static 1:1 host:guest location)
RAM,               0x0        - (memory size selected less then 1GB)
ROM,               0x40800000 - 0x40C00000 (4MB mac rom)  (static 1:1 
host:guest location)

Real addressing == "normal" allocation where memory locations are dynamic, 
and we translate addresses to match
Direct addressing == memory is directly addressed, mostly used on native 
PowerPC?
Nat_mem offset == ???, guessing it's for native PowerPC

It looks given the code below that the Macintosh has to be patched to use 
the host memory
addresses vs the emulator doing the memory translation (SheepShear acting as 
a mmu to the guest)
https://github.com/kallisti5/sheepshear/blob/master/src/kpx_cpu/src/cpu/vm.hpp#L185

The reason I ask here is because these changes could be pulled upstream to 
SheepShaver.

  -- Thanks!
    Alex