Re: [B2-devel] DUDA: HWMMU PARA SHEEPSHAVER?

[Steven K. <vz_...@ya...>]

Gracias Por aclararme la situacion.
 
Otra Pregunta, ¿Es Posible utilizar la ROM PowerMac 6100 con sheepshaver para windows?
 
Otra vez, Gracias

Gwenole Beauchesne <gb....@fr...> wrote:
Le jeudi, 7 avr 2005, à 21:39 Europe/Paris, Steven Knoxville a écrit :

> Okay, pero entiendo que para el software PearPC existe un Parche de 
> nombre HWMMU que se encarga de utilizar la MMU i386 para emular una 
> MMU PowerPC, mi pregunta es ¿Es Posible modificar este parche para que 
> trabaje con SheepShaver y asi poder emular MacOS 9.1 y X que requeren 
> de una mmu para trabajar?

QEMU already implemented an HWMMU implementation, nothing new in 
PearPC. Basically, you use mmap() to map shared pages at specified 
locations (expected by MacOS). The problem is that on Linux/x86 
architectures with a default 3G/1.5G split, you will be limited by up 
to 3GB address space in user mode (the case here). Full HWMMU support 
on 32-bit systems requires a patch to host kernels and people may not 
be willing to do that. This limitation can be workarounded in the 
emulator but you still get suboptimal performance.

All in all, you don't want HWMMU. However, you may want MMU emulation 
to help understand how MacOS VM works and provide better native 
replacements. See, SheepShaver is a higher level emulator that 
virtually can replace any system function with native implementations 
for improved performance. *All* PowerPC MacOS version require an MMU, 
there are just ways to do without it.

I don't think MMU will ever be implemented into SheepShaver. However, I 
already experimented MOL with a CPU emulator in the past. My MMU 
emulation was inacurate so I had started to use QEMU implementation but 
time terribly dropped and when time came back I moved on to SheepShaver 
again with some bug fixes and other features.

BTW, adding MMU emulation to SheepShaver wouldn't have made it run 
MacOS X either. It's a totally different architecture. Emulating the 
MacOS X System is not interesting but enabling MacOS X Applications to 
run on another system is. That's the key difference in speed and 
integration.

If you look carefully, it's easier to emulate MacOS X than MacOS 9, 
simply because you have the MacOS X kernel sources: xnu. And, if you 
look carefully at xnu, you can find ways to virtualize the Mach VM 
layer, but that's not trivially simple but not that difficult either. 
At first, you will have the same limitations than HWMMU. But at least, 
this time, you can also restrict a little the user address space so 
that another trick can be used so that you don't get performance loss.


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