First of all for our RT-Linux/RTAI maintainers, i would sugest
to make parts of this thread a very big point in the FAQ, i lost
lot of time with something that was apparently a known problem.
Also a black list with devices that cause problems and a white list
with devices that have no known problems wouldn't be bad.
One big quiestion remains , what is so different in XFree 4.0.1
compared to XFree 3.3.6 ?! the s3virge driver in 3.3.6 isn't (much)
slower
than in 4.0.1 , but the latency is gone. The mga driver is slower but
here
also the latency is gone when using 3.3.6. The structure of XFree 4.0.1
gives us the posibility to patch the drivers when needed and only
distribute
those, that way there could be made lowlatency version of the drivers
without the
need for ppl to download multi mega byte tar/rpm files. (just like is
done
with the patches for the linux kernel )
Mark Vojkovich wrote:
>
> On Sat, 25 Nov 2000 [EMAIL PROTECTED] wrote:
>
> >
> > Andrew Morton reports that the S3 and Matrox cards are known to
> > have problems giving up the PCI bus.
>
> On many cards, Matrox for sure, it's virtually impossible
> to prevent PCI disconnects from happening. Matrox discusses
> this in their documentation, for instance, the G400 docs,
> section 4.1.2
>
> "PCI Retry Handling
>
> In certian situations the chip may not be able to repond
> to a PCI access immediately, therefore, a number of retry
> cycles will be generated. A retry will be asserted when:" ...
>
> [ a whole mess of cases including direct framebuffer accesses ]
>
> For real-time platforms you folks probably need to be using
> old ISA cards or something. Some PCI chipsets make the retry
> problem worse. LX chipset is infamous.
With realtime apllications i am very well willing to offer performace
for predicatble latency. By turning of the acceleration i seem to loose
more performance than needed though, i will see if i get a hand on the
docs
of matrox and VIA, and try to find the place where the latency is
caused.
>
> Mark.
>
- Erwin
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