> I know this is probably a question for Freescale directly,
> but I thought I would post here to see if anyone else has
> seen similar issues with the MPC85xx PCI under Linux.
>
> I'm using a Freescale MPC85xx (8541) processor and seeing an
> extreme slowness to the PCI bus.
>
> I'm attemping to do 2048 byte PCI burst reads from an
> external PCI master. So an external chip is the PCI master
> ("initiator") and the MPC85xx is the PCI slave ("target")
>
> When initiating the PCI burst read, there is a 270 ns delay
> from the MPC85xx claiming the transaction (DEVSEL# going low)
> to being ready (TRDY# going low). Then 64 bytes (a single
> cacheline) are transferred, and TRDY# goes inactive. Next,
> STOP# goes low, terminating the transfer. I believe this is
> considered a PCI DISCONNECT type 1 since IRDY# is active the
> entire time.
>
The 85xx cacheline is 32 bytes.
Did you enable Memory Read Multiple command of your PCI master?
> What I would expect is that the entire 2048 bytes are
> transferred in one PCI bus mastership, but instead there are
> several re-arbitrations and long delays in between several 64
> byte transfers.
>
> Additional info:
> The PCI bus is 64bit running at 66 MHz.
> I'm running a modified Linux 2.6.9 kernel (elinos-111).
> The PCI CCSR piwar1 = 0xa0f4401d.
>
> Freescale has an FAQ 21021 that describes having a PCI
> DISCONNECT 2, which sounds similar to my problem, but I've
> already confirmed I'm doing what the FAQ suggests (enable
> prefetching in the piwar register)
> (http://www.freescale.com/webapp/sps/utils/SingleFaq.jsp?FAQ-2
1021.xml)
Any thoughts/suggestions would be appreciated,
Tim
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