Re: Emulated macppc with qemu

[Michael <macallan%netbsd.org@localhost>]

Hello,

On Mon, 5 Apr 2021 10:16:00 -0700
Jason Thorpe <thorpej%me.com@localhost> wrote:

> > On Apr 5, 2021, at 9:30 AM, Michael <macallan%netbsd.org@localhost> wrote:
> > 
> > This caught my eye a bit late, but...
> > How is >2GB RAM supposed to work on even an emulated 32bit macppc?
> > The address space is divided up by hardware into 0x0 - 0x7fffffff for
> > RAM, and above that lives PCI space, various onboard devices and
> > firmware ROMs. If you map extra RAM into this range NetBSD will need
> > adjustments since we BAT-map most of this space 1:1.
> > That said, it shouldn't be hard to get this working, just have to pay
> > more attention when entering BAT mappings, and the RAM counting code
> > may ignore areas above 0x80000000.  
> 
> Right, this is what I meant in my previous message.  The physical
> memory map on G4 Macs doesn't have room for more than 2G of RAM.

.. or any other that I know of. Even on G5s the 32bit range looks like
a 32bit mac, with any additional RAM appearing above 4GB. 

> Mark -- it might be a good idea to place a limit of 2G in the 32-bit
> Mac emulation.

In theory it would be possible to emulate a weirdo mac with RAM in the
lower 3GB and PCI space above that, I don't think any of our code
actually depends on mac-io ( and therefore openpic etc. ) living at
0x80000000 - if the OF tree said it's at 0xc0000000 that part would
probably Just Work(tm)...
Now of course I don't know if that's what qemu does or if it actually
supports such a thing in the first place. 

have fun
Michael