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Old 02-18-2005, 09:55 PM
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Default Issues with a batch of Virtex-II chips


I'm using Virtex-II (XC2V1000-FF896-4C) in one of the product which we have
been selling for over 3 years. Recently we got "new" batch of Virtex-II
chips and problems started to arise. So far I have isolated PCBs with three
different batch of Virtex-II chips:

Batch A:

Batch B:

Batch C:

All the chips in batch A have the suffix AFT301, all the chips in batch B
have the suffix AGT0409,...
PCBs with chips from batch B and C are working fine, on the other hand none
of the 42 PCBs, where chips from batch A are used are working. PCBs are the
same (same revision) for all the products, all other components (ZBTRAMs,
DDR SDRAMS, passive components,....) are the same. All voltages are within
the safe margins, all input clocks are clean. All the affected boards pass
the JTAG test, in other words we didn't find any soldering errors, short
circuits, vias without metallization, wrong resistors or capacitors,
incorrectly oriented diodes or capacitors... or any other error we could
think of. We got all the chips in a sealed package. PCBs were tested at
different temperatures (from 8 degrees Celsius to 46). Only the PCBs with
chips from batch A don't work. Let me explain what precisely is not working.

I'm using 6 DCMs to generate clocks for ZBTRAM, DDR, System, ConfigBus,...
and two DCMs don't set the locked signal after I release them sequentially
from reset. I don't know if other parts of the design (the parts which don't
use ZBTRAM clock) don't work either, because the missing clock is a fatal
error and I didn't have the time to investigate further in that direction.
Working freq. of ZBTRAM is 120MHz, DDR is working at 166MHz, System at
100MHz, ConfigBus at 10MHz,...

We are currently using ISE 5.2 SP3 for this design. I have verified the bit
stream by reading it back from the chip and it's ok.
Two coworkers, guys from the production and I are working on solving this
problem for the last two days and we are almost out of ideas what else we
could try, except replace the problematic chips with the non-problematic. I
can't use ISE 6.1 or newer because the routing is not successful or ISE
simply doesn't meet the timing constraints (the chip is 99% full).

Have you experienced anything similar in the past? How did you solve the
problem? Do you have any ideas/suggestions what else I could try? I couldn't
find any document on the xilinx web site explaining the detailed chip
signatures. I would like to know, what AFT0301 stands for? Is this the
product date, production line, factory code...? I would like to know, when
the chips have been manufactured (how old are they)?

I guess we'll have a competition in the company next week. And the goal will
be; who can throw virtex-II the farthest... Ok, I'm just joking, but I
needed to vent...argh...

Igor Bizjak

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