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 Trace fail 

Last post Fri, Jun 28 2013 6:04 AM by TAM1. 3 replies.
Started by Buvna 27 Jun 2013 05:15 AM. Topic has 3 replies and 447 views
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  • Thu, Jun 27 2013 5:15 AM

    • Buvna
    • Top 500 Contributor
    • Joined on Fri, May 31 2013
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    • Points 245
    Trace fail Reply

    Hello,

    Im running assertions on IFV with witness check defined as trace. The trace fails and the assertion passes. What does this mean?

    Thanks. 

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    • Post Points: 20
  • Thu, Jun 27 2013 6:51 AM

    • TAM1
    • Top 75 Contributor
    • Joined on Thu, Jul 17 2008
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    Re: Trace fail Reply

    There are a couple of ways this can happen. They are based on the principle that an assertion "passes" if IFV cannot find a sequence in which the assertion reaches an error state.

     So, if you have an assertion that looks like "trigger_sequence |-> suffix_sequence", then the assertion will "pass" if the trigger_sequence can never occur. Since the trigger can't occur, the suffix doesn't need to be checked. This is by far the most common way to get the results you have described. 

     You can check to see if the trigger is possible, given your constraints, by issuing the TCL command "define witness_check trigger".

    • Post Points: 20
  • Thu, Jun 27 2013 9:14 PM

    • Buvna
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    • Joined on Fri, May 31 2013
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    Re: Trace fail Reply

    Hello,

    Thanks for the reply.

    When I enabled changed witness to trigger, it failed too.

    This essentially means I needn't bother about this assertion right?

    Thanks 

    • Post Points: 20
  • Fri, Jun 28 2013 6:04 AM

    • TAM1
    • Top 75 Contributor
    • Joined on Thu, Jul 17 2008
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    Re: Trace fail Reply

    Well, I would worry about it. :-)

    When you  wrote the assertion you obviously thought that the trigger was possible and that you needed to check for certain behavior when it occurred. If IFV reports that the trigger is impossible you need to figure out what that means. Why can't the trigger occur? Did you write it correctly? Is there a bug in the DUT that makes behavior you expected to be legal impossible? Why did someone give you a specification describing behavior for conditions that can never be seen?

    • Post Points: 5
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Started by Buvna at 27 Jun 2013 05:15 AM. Topic has 3 replies.