very slow response of memory read with VIA KT133 chipset

[yang.can.mei@philips.com]

Hi PCI experts,

Could you guys give a little light on following problem.

We are testing our PCI device. We got some problems with PCI interface of KT133 chipset and we couldn't find out The system is:

CPU: AMD Athelon/ Duron
Motherboard:K7T Pro2 from MSI and KT7-RAID from ABIT
Chipset: KT133 chipset(VT8363) and SouthBridge VT82C686A from VIA
OS: Win98SE

We found:
. The master memory write of our PCI device works fine, no wait cycle(I guess this is because all the write were posted in VT8363)
. But each master memory read gets to wait an abnormally long time to obtain response from target(I guess this is due to VT8363, not the real memory). The wait cycle are around 18 for MSI motherboard and 45 PCI cycles for ABIT motherboard. In both cases, 
the waiting time is longer than defined value in PCI specification.
. We changed different memory, the problem still exists.
. We tested different PCI device of same class, the waiting time is basically same, but the other PCI device work, 
. More seriously,our PCI device, didn't work. The target(memory controller) didn't reply with any data after it asserted DEVSEL(that means memory controller has finished decode of command address) to master (our device), but didn't give anything 
thereafter. Then our device must die because our PCI device saw DEVSEL from target. If our PCI master didn't see DEVSEL asserted by target, the master could issue a master abort.

>From our understanding of PCI spec., memory read should be very fast from PCI viewpoint, it is easy to meet the latency requirement for most PCI bridge designs. So our question is,
Have you met the same problem? What is the rootcause of this slow response of memory read?

Thanks in advance

Paul Yang C.M.
Philips Semiconductors