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SubjectRe: VGA PCI IO port reservations
Russell King wrote:
>
> Brian Gerst writes:
> > This is an artifact from the ISA 10-bit IO bus. Many ISA cards do not
> > decode all 16 address bits so you get aliases of the 0x100-0x3ff region
> > throughout IO space. PCI cards should only use the first 256 ports of
> > any 1k block to avoid aliases unless they claim the base alias. For
> > example, all the xxe8 addresses for the S3 are aliases of 0x02e8 to an
> > ISA card. Video cards are an exception to the general rule because they
> > have to support all the legacy VGA crap.
>
> No. All xxe8 addresses access specific registers. For example:
>
> 0x9ea8 is the drawing command
> 0xa2e8 is the background colour register
> 0xa6e8 is the foreground colour register
>
> So, as you see they aren't aliases.

Oh yeah, if you are writing for S3 specifically, you can do 100% MMIO,
and simply turn off all I/O decoding. Check out Keith Packard's
kdrive/s3trio in the XFree86 tree...

Jeff


--
Jeff Garzik |
Building 1024 | The chief enemy of creativity is "good" sense
MandrakeSoft | -- Picasso
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