On Fri, 12 Jul 2002 [EMAIL PROTECTED] wrote:
> Hello Expert lixt
>
> Does anyone know if there is a standard way to access legacy VGA
> registers through mappe-memory registers in most video cards. I
It's not standard. I think nearly all cards can do it, and
there are some similarities between a subset of cards, but there's
no standard way, either in where the registers are mapped or
how they are laid out within that mapping.
> am asking this question because in woul like to be able to driver
> a PCI card with the normal Xserver while driving an AGP card with
> a custom driver. The custom driver would make use of legacy addresses
> but doing this without altering the behavior of both cards is
> my problem.
>
As two separate processes this will be difficult. Even for
an XFree86 driver that can manage without doing any port I/O,
and many are that way, you still need legacy access to save
the fonts. Perhaps if the Xserver was on the secondary card
so it didn't have to save fonts, it might never need to touch
the legacy vga. But still, there probably needs to be some
X-server hacking to keep XFree86 from disabling access to your
vga card. I think in many cases it probably proactively pulls
the other card off of the bus to keep it from interfering with
the operating X-server. Egbert Eich is the expert in this area.
XFree86 actually has a mechanism where it can run N cards that
only do port I/O to legacy registers simultaneously. It does
this by enabling and disabling access at appropriate times.
But these are all managed within the same process so it can
keep track of this stuff. A third party would complicate things.
Mark.
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