NuBus PowerMacs and PDM video

Michael R. Zucca mrz5149 at
Wed Feb 10 13:35:49 EST 1999

At 7:14 AM -0500 2/9/99, BenH wrote:

>I'm doing some experiments with the MMU (learning it's usage). The goal
>is to add some better bootstrap code to BootX (get rid of the -622 error
>with MacOS VM) and to add support for the rather "special" memory
>mappings of the NuBus PowerMacs.

The PDM PowerMacs have their guts designed after 68k macs. They have the
same weird problems like aliasing, and a discontiguous memory.

>I beleive MkLinux booter moves it elswhere, but I don't know how to do
>that (I don't have infos about the chip and I don't have one of those
>machines to test with).

You just need to know the physical base address of the frame buffer.
Once you know that you can just rewrite the page tables to put the
frame buffer anywhere you'd like it.

You need to write a program under MacOS that will find a physical address
for a given virtual address. You'll probably need to do this in assembly
or there may even be a toolbox call that will do this for you.

 Michael Zucca - mrz5149 at -
 "I will choose a path that's clear. I will choose Freewill. "
  --Rush, Freewill

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