NuBus PowerMacs and PDM video

BenH bh40 at
Wed Feb 10 22:49:19 EST 1999

On Tue, Feb 9, 1999, Michael R. Zucca <mrz5149 at> wrote:

>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.

I was thinking about the machines that store the framebuffer in main
memory (I beleive the 6100 does this). In this case, several people told
me that the physical address was actually 0. Anyway, I now have some code
to mess with the video controller, so I will be able to work around this

>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.

There is a MacOS call for logical->physical mappings. The base address
sent by BootX to the kernel is already a physical address (actually both
are sent with BootX >= 1.0.2b1)

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