RE: [pci] Clock Domain Issues

[Dave Kroetsch <dkroetsch@videolocus.com>]

Miha, 

>From what I've seen, (and from what the tools tell me)
this is not a valid design constraint?  Can you explain
what you're actually trying to do with those statements?

	Dave Kroetsch

-----Original Message-----
From: Miha Dolenc [mailto:mihad@opencores.org]
Sent: Monday, April 29, 2002 4:56 AM
To: pci@opencores.org
Subject: Re: [pci] Clock Domain Issues


We ran it at 33MHz on PCI side and 22MHz on the other and it ran for a few
days with no problems.
The target was used mainly for configuration, master was actually
transferring the data.
Have you tried tightening the constraints and recompile the core?

Example:

TIMESPEC "TS_CLK_2_CLK2" = FROM : "CLK"     : TO : "CLK2" : 5 ;
TIMESPEC "TS_CLK2_2_CLK" = FROM : "CLK2" : TO :  "CLK"     : 5 ;

where CLK would be PCI clock and CLK2 WISHBONE clock. These go into ucf
file.

Regards,
Miha Dolenc

----- Original Message -----
From: "Dave Kroetsch" <dkroetsch@videolocus.com>
To: <pci@opencores.org>
Sent: Friday, April 26, 2002 5:41 PM
Subject: [pci] Clock Domain Issues


> Has anyone been successful in running the PCI core with the PCI side
> running at one clock and the wishbone running off another?  I have tried
> running the PCI side at 33MHz and the wishbone side at various
> frequencies ranging from 6MHz to 60MHz, and I'm running into problems.
>
> I'm only testing the PCI target right now (as a guest in a PC system),
> and I'm using the OpenCore DMA  register file as a target.  (I have also
> tried my own register as a target) I've brought some of the wishbone
> signals (including cyc, ack, we, stb...) out so I can scope them.  The
> tests I have tried include:
> 1) Writing single words
> 2) reading single words
> 3) writing bursts of 2 words
> 4) writing bursts in the pattern 1-2-1
>
> I'm having problems with the PCI bridge generating improper wishbone
> accesses and even hanging the PC!  This is being implemented on a
> Xilinx Virtex2 FPGA in a PC running linux.
>
> Some of the symptoms include:
> 1) The OpenCore PCI Bridge will generate extra wishbone
>                  transactions.  eg. a PCI write of 4 words will sometimes
>                  work properly and sometimes generate 5 or 6 word writes
>                  on the wishbone bus.
>
> 2) The bridge will enter a state where NO transactions from
>                  the PCI side will even make it across to the wishbone
bus,
>                  and the transactions eventually time out
>
> 3) The bridge will hang, such that wishbone transactions are
>                  CONSTANTLY being initiated and no finishing (despite the
>                  fact that they are being ACKed repeatedly)
>
>             4) The bridge enters a state where it ends EVERY attempted
>                   transaction with a PCI STOPn and never asserts TRDYn.
>                   This never allows the transaction to succeed.  The PC
>                   continuously retries until a watchdog kicks, and it
reboots.
>
> If I run the wishbone side at the PCI_CLK, this all seems to go away.  It
> would seem there is a problem with the clock domain crossing.  Can
> anyone provide any insight?
>
> Thanks,
> Dave Kroetsch
>              dkroetsch@videolocus.com
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