signal update problem

Discussion in 'VHDL' started by Kuan Zhou, Mar 11, 2005.

  1. Kuan Zhou

    Kuan Zhou Guest

    Hi,

    I have a doubt on the signal update in the architectural body. Suppose
    you have multiple processes and each process has some WAIT statements. Do
    the signals get updated once all the activated processes are reaching the
    WAIT statements?
    If the processes have sensitivity list instead of WAIT statements, the
    signals must be updated once the activated processes finish the current
    loop and come back to the beginning of the processes. Am I right?

    Kuan
     
    Kuan Zhou, Mar 11, 2005
    #1
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  2. "Kuan Zhou" <> wrote in message
    news:p...
    > Hi,
    >
    > I have a doubt on the signal update in the architectural body. Suppose
    > you have multiple processes and each process has some WAIT statements. Do
    > the signals get updated once all the activated processes are reaching the
    > WAIT statements?


    Yes. The idea is that processes communicate via signals. To get the order
    independent execution of the concurrent processes the simiulation cycle has
    two stages:
    1- execute all (sensitive) processes.
    2- update the signals

    In this way all processes use the same value of the signals ==> order
    independent execution!.
    The update of a signal can of course be postponed to a later time if you
    added a time i.e. y <= x after 5 ns;

    > If the processes have sensitivity list instead of WAIT statements, the
    > signals must be updated once the activated processes finish the current
    > loop and come back to the beginning of the processes. Am I right?
    >

    process ("sensitivity list")
    begin
    bla bla bla
    end process;

    is 'translated' to:

    process
    begin
    bla bla bla
    wait on "sensitivity list";
    end process;

    And you already have the answer of this in the first part of your question.
    So you are right here too.

    Regards,
    Egbert Molenkamp
     
    Egbert Molenkamp, Mar 11, 2005
    #2
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