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SubjectRe: Next round of console patches
On Wed, 2 Sep 1998, Gerd Knorr wrote:
> On Wed, 2 Sep 1998, Vojtech Pavlik wrote:
> > On Wed, Sep 02, 1998 at 08:20:32AM +0200, Gerd Knorr wrote:
> > > There is. The VESA BIOS will tell you (a) how much video memory the board
> > > has installed and (b) where the linear framebuffer starts. vesafb (well,
> > > the real mode boot code) asks the BIOS for these values and uses this for
> > > the framebuffer device. And for exactly this area the mtrr entry is added.
> > >
> > > Assuming legal framebuffer space and MMIO don't overlap, this works fine.
> >
> > As far as I know, this assumption is not true at least for Mach64 based VGA
> > cards - they map their MMIO over the last kilobyte of video RAM in the
> > aperture.
> ^^^^^^^^
> Could you explain this? My dictionary has'nt conputer-speak translation
> for this...
> Does it really mean the video memory and mmio overlap? Or is this some
> larger area (say 16 MB space) for graphics I/O with the framebuffer (say 4
> MB) at the start and 1k MMIO at the end and some unused space inbetween?

My ATI Mach64 GT (RAGE II+) has 2 PCI blocks: one of 16 MB and one of 4 KB.

The first 8 MB of the 16 MB region is a little endian aperture (window) to the
frame buffer memory. The second 8 MB is a big endian aperture to the same frame
buffer memory. By default, the last 2 KB of the little endian aperture (i.e.
at base+8MB-2KB) contains the MMIO registers.

The 4 KB region is the auxiliary register aperture: it contains the same MMIO

You can chose which of the two register apertures you want to enable, or even



Geert Uytterhoeven
Wavelets, Linux/{m68k~Amiga,PPC~CHRP}
Department of Computer Science -- Katholieke Universiteit Leuven -- Belgium

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