DCM start up

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I've got a DCM as part of a 4 byte Aurora implementation on a VII Pro.
Sometimes after JTAG configuration the DCM just won't lock (hence the
ChannelUp never happens either). Once it's decided not to work, doing the
reconfiguration again or resetting has no effect. If I then configure with
an old version of code (also with a power cycle) it works OK with old and
new code. Are there any tricks I should know about here either in the VHDL
or settings in the tools that anyone can tell me about please as I really
need to get around this problem?

TIA,

Rog.



Re: DCM start up
Roger,

What is the status of the DCM is this condition (the status byte)?

It may be that the CLKFB signal isn't right while the DCM attempts to
lock, and it either can't lock (taps on delay lines overflow or
underflow), or it locks in the wrong place.

Try resetting the DCM after a delay to allow oscillators and all
circuitry to stabalize.

Austin



Roger wrote:

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Re: DCM start up

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May not be related to the DCM problem, but starting the PPC from JTAG in
a V2Pro was also problematic (random failure, probability > 50%) unless
the "Pulse Prog" option was ticked in IMPACT.

My webcase didn't get a clear explanation from Xilinx, so I suggest
these two startup problems MAY be related, and (if you're using Impact)
it's a quick and easy change to try. (If you're accessing JTAG by some
other tool, there must be some way to pulse the PROG pin). I'd be
interested to hear if this clears the problem.

- Brian

Re: DCM start up
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Do you have a post-configuration startup reset for the DCM's ?

see Answer Record 11778:
    "Virtex/-E/-II/-II Pro, Spartan-II/-IIE/-3 - Device configures
     correctly after PROG is pulsed, but DLL/DCM/DCI does
     not function correctly when reconfigured

 Also note, when configuring a device from JTAG that also has an
external configuration PROM, it is best to set the mode pins to JTAG,
and/or erase the PROM, to avoid weird configuration problems.
(Answer Records 9013, 16829, 22255)

Brian


Re: DCM start up
Just read your replies. Lots of good stuff to try. I'll do some experiments.

Thanks very much for taking the time to reply.

Merry Christmas

Rog.

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