Re: Problem w/ Matrox Millenium

[Tom Hicks <thicks@fore.com>]

> I'm seeing a problem when using one of our PCI controllers in conjunction
> with a Matrox Millenium graphics card.  It appears that the Matrox card is
> retrying (for long periods of time) a mem-write (from the CPU) to its 
> address space.  Our controller gets every other bus cycle and is trying to 
> master a memory-read from system memory.  We are also getting continually
> retried until we fail (meaning that our real time requirements simply aren't
> met.)  We are seeing somewhere in excess of 256 retries.
> 
> I suspect that it is the Matrox card retrying our cycle, although I can't
> prove this.  I can't think of a reason why the host bridge would be doing 
> the retrying unless there is some strange side effect from the retries the 
> Matrox card is issuing for its own cycles.  We have tested this on two
> different Intel chipsets (HX and FX) and still see the problem.  I've also 
> heard problem reports from modem users (overruns) when using the Matrox card
> which seems to indicate the same problem.
> 
> Has anybody seen similar problems or problems with the Matrox card in
> particular?  Is there any explicit requirements in the PCI spec the
> prohibits a device from retrying cycles other than it's own?  

What you are seeing is the ordering requirements of PCI being maintained.
There is a write in the north-to-south bridge posting buffer, which is being
retried by the Matrox card.  Your read from system memory cannot proceed until
that write completes.  So if the Matrox card is retrying the writes forever,
there is a problem with their hardware and/or software.
~ðà