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Altera_Forum's avatar
Altera_Forum
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15 years ago

timing simulation vs real

Hello

I am trying to compare a timing simulation (with specified pins) of a simple verilog XOR assignment in Quartus II to the actual timing on a Flex EPF10K70 device. That is to say, I am comparing a simulated v.s. real propagation delay between an input state change to output state change of the XOR function.

I notice that the simulation shows a delay of approximately 27ns, but in hardware I see a consistent delay of only ~7.5ns for the same sequence (one input goes from low to high).

Does anyone know why this might be? (Apologies: I am new to this)

Thanks

3 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    15 years ago

    Yes, that is what I thought too. I cant see why it should be that slow, going by the datasheet, and obviously the real thing is not that slow. I can make it simulate slightly faster by automatically selecting input/output pins but this yields a simulated 5ns improvement only (still >20ns for such a simple assignment).

    I tried repeating the experiment using an EPM3032ATC44-4 (4ns). Both the timing simulation and real device timing agree pretty well and both match the performance that I would expect.

    So is there maybe a setting somewhere for the FLEX device that I am missing? This is an early version of quartus II (v4).
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    15 years ago

    --- Quote Start ---

    Yes, that is what I thought too. I cant see why it should be that slow, going by the datasheet, and obviously the real thing is not that slow. I can make it simulate slightly faster by automatically selecting input/output pins but this yields a simulated 5ns improvement only (still >20ns for such a simple assignment).

    I tried repeating the experiment using an EPM3032ATC44-4 (4ns). Both the timing simulation and real device timing agree pretty well and both match the performance that I would expect.

    So is there maybe a setting somewhere for the FLEX device that I am missing? This is an early version of quartus II (v4).

    --- Quote End ---

    Hi,

    what are the results of the timing analysis ?

    Kind regards

    GPK