Re: Next round of console patches
Vojtech Pavlik (vojtech@twilight.ucw.cz)
Wed, 2 Sep 1998 20:25:48 +0200
On Wed, Sep 02, 1998 at 06:56:06PM +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...
Sort of 'address space which maps to that card' ... I think, though I'm
no native english speaker as well, that this really is similar to the optical
meaning of aperture.
> 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?
Unfortunately for the Mach64s, the MMIO registers really overlap with the
memory, and thus the last 1-2 kilobytes of the video ram are not useable.
Vojtech
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