Post-Route Simulation does not give output for the first clock cycle

Discussion in 'VHDL' started by Drew, Apr 17, 2007.

  1. Drew

    Drew Guest

    Hi,

    I designed a 3 stage pipelined floating point adder/subtractor (IEEE
    754 floating point arithmetic).

    I am using Xilinx ISE 9.1a environment to code and Modelsim to
    simulate.

    I am getting correct outputs for all the clock cycles in behavioral
    simulation. However, in Post-Route simulation, I am not getting
    output for the first data pair given for the arithmetic. In the next
    clock cycles, output is coming correctly. When I increased the period
    to 200 ns, output is coming correctly in the first clock cycle also.
    But, I did not understand why it is giving correct output when the
    period is increased to 200 ns from 80 ns.

    In the detailed Design summary produced after the Post-Route
    simulation, I saw that the minimum time period is 24 ns. But, I am
    getting output for the first clock cycle only when the period is
    increased to 200 ns. Please throw some light about what is happening.

    Thanks and Regards,
    Vamsi.
     
    Drew, Apr 17, 2007
    #1
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