From: dawes@physics.su.OZ.AU (David Dawes) Subject: Re: XFree 1.1 with T8900; mixed results. Date: 28 Dec 1992 23:11:23 GMT
In article <1992Dec28.181842.21972@Informatik.TU-Muenchen.DE> roell@informatik.tu-muenchen.de (Thomas Roell) writes:
>> 2. why does the 256 color Trident display driver only support
>> T8900C chips? What's this annoying difference between the
>> T8900B and C?
>
>That's a very trivial reason. For some X stuff you need to have access
>to a source byte and a destination byte at the same time. If you deal
>with SVGA's which cannot map their whole 1MB video memory into the
>CPU's address space, you have to do banking. If you also have to
>fullfill the upper constraint, then you see that you need to have two
>banks which can be used independantly (since source and destination of
>the operation might not be in the same bank).
>
>The TVGA8900B supports only ONE bank, while the TVGA8900C supports TWO
>banks.
The XFree86 tvga driver actually uses the TVGA8900C in single-bank mode.
Apparently it benchmarked quicker in that mode than in the dual-bank
mode (don't ask me why -- I was suprised at the results). We use a
different bitblt routine in this case.
For this reason I expected that our driver might work on the 8900B, but
it seems that it doesn't. The only other difference that I know of
between the 8900B and 8900C is that some registers are read-only on the B
and R/W on the C. If someone with an 8900B and X source on-line wants
to look into this, please let us know.
David