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use events in spectreMDL expressions

Zol

I am exploring spectreMDL. One of the feature I would like to use at the  moment is to stop a transient simulation at a given condition. My current DUT needs to be configured, and it takes different amount of time depending on the PVT corners.  I detect the time-event when the DUT is ready with an assert. I use this assert in a paramset file. Is there a way to either reference an assert, or to define an event and use it in MDL expressions? In the example below I would like to disable the cross() function before an event. How could I do it?

alias measurement stop_after_1cycle {
  export real event
  run tran
  event = cross(sig=V(sig), dir='rise, thresh=1.25, n=2, start=@(myassert))
}
run stop_after_1cycle

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  • ShawnLogan

    Dear Zol,

    Zol said:
    One of the feature I would like to use at the  moment is to stop a transient simulation at a given condition. My current DUT needs to be configured, and it takes different amount of time depending on the PVT corners.  I detect the time-event when the DUT is ready with an assert. I use this assert in a paramset file. Is there a way to either reference an assert, or to define an event and use it in MDL expressions?

    I am not an MDL expert, but if I understand your need, it seems that the autostop MDL function will provide a possible solution. If you define a cross() function measurement to detect when your DUT is configured (or the falling edge of a pulse width of Tdelay after it is configured to allow for a delay time after it is configured), the simulation will stop after the cross() function is evaluated. Hence, although the configuration time is dependent on each simulation corner, each simulation corner transient simulation will only run for the time it is required to configure plus any fixed delay time,Tdelay, after you detect its configuration is completed. There is an example of the use of the autostop command in the MDL reference manual on page 44 at URL:

    https://support.cadence.com/apex/techpubDocViewerPage?xmlName=mdlref.xml&title=Spectre%20Circuit%20Simulator%20Measurement%20Description%20Language%20User%20Guide%20and%20Reference%20--%20Defining%20and%20Using%20Measurement%20Aliases%20-%20Autostop&hash=pgfId-1044794&c_version=21.1&path=mdlref/mdlref21.1/chap1.html#pgfId-1044794

    and a Troubleshooting article at URL:

    https://support.cadence.com/apex/ArticleAttachmentPortal?id=a1Od0000000nVHHEA2&pageName=ArticleContent

    I hope I understood your need correctly Zol and this provides some insight.

    Shawn

  • Zol
    in reply to ShawnLogan

    Hi Shawn,

    Thanks for the links. I am already using the autostop option and MDL to stop the simulations. I was looking for a way to define the value of the "start=" field in the above cross() function dynamically. I wish I could use an assert there for consistency, because I use this assert a paramsetfile of the tran analysis. 

    The workaround what I've found is to use another function to deliver the intended value of the start field:

    event = cross(sig=V(vcp_up), dir='rise, thresh=1.25, n=2, start=cross(sig=V(v_assert), dir='fall, thresh=0.75, start=20u)+2u )

    Regards,
    Zoltan

  • Andrew Beckett
    in reply to Zol

    Zoltan,

    I don't believe it is possible (as far as I know) to use an assert as an event to define a time in an MDL expression. I can see how that would be useful, but don't think it's possible at the moment (I may be mistaken, but I'm not aware of a way). I would suggest you contact customer support (create a case on the support site) to check, and also to file an enhancement if it's not available right now.

    Regards,

    Andrew

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  • Andrew Beckett
    in reply to Zol

    Zoltan,

    I don't believe it is possible (as far as I know) to use an assert as an event to define a time in an MDL expression. I can see how that would be useful, but don't think it's possible at the moment (I may be mistaken, but I'm not aware of a way). I would suggest you contact customer support (create a case on the support site) to check, and also to file an enhancement if it's not available right now.

    Regards,

    Andrew

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