FPGA hangs

First: check that both boards really operate with the same input signals. Swap the boards and check where the failure moves. Next: Vary ambient temperature and also (separately) Vcc, and note their impact on the behavior.

These two simple test should give you some clues. "Minutes" almost always points to a temperature effect, unless you have extremely long counters in the chip. It could also be caused by hanging undriven pins that very slowly drift High or Low. Hope this helps. Peter Alfke

Dear peter, Thank you for your reply. I have some questions:

The enviroment, input signals, temperature are exactly the same for both boards.

Power on these boards comes from a good DC/DC converter from DATEL. There is no power variation on the boards.

I have some undriven and UNUSED pin on the fpga (XC2S150E). No signal handled by these pins. Is it important? Should I connect these pins to ground or Vcc ?

regards. M. Naderi

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It sure sounds like a temperature problem. Variations in process could cause one part to fail at one temperature and the other to operate fine. I once had a customer that reported that my design would work for several minutes and then start to fail. He blew some coolant on it and it started working again. He had to end up beefing up the fan system. Xilinx parts tend to use a little more power than expected.

I also had a customer with a similar symptom and the cause was insufficient decoupling capacitance, so you might check that as well. Those caps seem like they're not doing much, but they are important and you should have one for eac VCC pin.

-Kevin

High...

A floating input that is not used is an unlikely source or problems. But you can make sure by configuring your device to drive these pins to a given value, even if it is just a pullup.