Hi !
> Here is a interesting question which I hope you have the answer to. For
> cards that lock when you acccess the framebuffer and accel engine. Does
> this happen when you access any part of the framebuffer while the accel
> engine is running or only when you access the area of the framebuffer
> which the accel engine is trying also to update?
Can be any. This behaviour is usually a bug.
I'll explain it a little further below:
It is pretty common for concurrent access causing image corruption, as this
can be caused by something as simple as missing arbitration for Video RAM
access.
Now if two devices (the PCI-to-cardmem-bridge and the accelerator) try to
concurrently drive the VidRAM bus lines, this will cause a major messup.
Often, you have no decent arbitration for this situation, which can cause
anything between undrawn pixels (when arbitration is in place, but basically
just discards the looser's data), corrupted pixels (when the data somehow
gets wire-combined), and large areas of corrupt pixels due to interference
in the addressing part.
Now you asked for the cards that lock up. There are several possible reasons
for that:
1. An arbitration clash like described above, that triggers a severe fault
condition within the chipset itself, due to the inconsistent data on the
bus. E.g. some blocking logic for arbitrating access for the RAMDAC readout
part might get confused and never give back access to the rest, thus
eventually locking up the chip at the next PCI-access to the framebuffer,
which will never complete.
Similar unrecoverable situations might arise, if the output logic of the
two bus drivers see the clash due to the overload produced and thus resort
to safeguarding themselves by going TriState.
2. A "device busy" situation which can be caused by the running accelerator
function being performed by the part that normally does PCI decoding or
similar. This may lead to a bus lock condition on the PCI bus, if the busy
condition thus produces erraneous responses to PCI bus transactions.
3. Additional problems might arise, if the card is capable of DMA transfers.
Then you could get similar problems to 1. on the PCI bus, if the PCI
interfacing is buggy.
CU, ANdy
--
Andreas Beck | Email : <[EMAIL PROTECTED]>
