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 short circuit problems in P & R 

Last post Mon, Nov 12 2012 12:19 PM by fitz. 5 replies.
Started by quiet 17 Oct 2012 01:42 AM. Topic has 5 replies and 1571 views
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  • Wed, Oct 17 2012 1:42 AM

    • quiet
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    • Joined on Mon, Aug 6 2012
    • Posts 13
    • Points 215
    short circuit problems in P & R Reply

    I'm using layer 3 and layer 4 for the power routing, so there are many vias through layer 3, layer 2 to layer 1.

    Then there are some short circuit problems when some signals pass through the vias. Is there any option to avoid this kind of problems? Can't the tool detect these short problems and avoid these?

    Thanks.


    • Post Points: 20
  • Wed, Oct 17 2012 7:57 AM

    • Scrivner
    • Top 100 Contributor
    • Joined on Thu, Oct 9 2008
    • Ridgeland, MS
    • Posts 75
    • Points 1,475
    Re: short circuit problems in P & R Reply

    Without seeing the power route floorplan it is difficult to tell what the problem is but if the router is creating shorts through power vias it sounds like your design is too congested by the power vias. Could you post a picture of your floorplan showing the power routing?

    • Post Points: 20
  • Thu, Nov 1 2012 6:36 AM

    • quiet
    • Not Ranked
    • Joined on Mon, Aug 6 2012
    • Posts 13
    • Points 215
    Re: short circuit problems in P & R Reply

    I have posted part of the power routing.

    Could I control the power vias by configuring the tool? or I just remove the vias that cause the short circuit?

    Thanks.

    • Post Points: 20
  • Tue, Nov 6 2012 5:47 AM

    • fitz
    • Top 150 Contributor
    • Joined on Wed, Aug 4 2010
    • Kanata, Ontario
    • Posts 56
    • Points 745
    Re: short circuit problems in P & R Reply

     Two possible solutions

    A) pre-place filler cells under all of your vertical power stripes to prevent standard cell placement  in the power via stack shadow.

    B) reduce the size of the power via stack with  addStripe option -max_via_size

     

    Shawn

    • Post Points: 20
  • Tue, Nov 6 2012 7:37 AM

    • quiet
    • Not Ranked
    • Joined on Mon, Aug 6 2012
    • Posts 13
    • Points 215
    Re: short circuit problems in P & R Reply

    Actually I have already put the place blockage under those stripes, so there isn't any standard cell under the strips.

    The problem is the routing lines passing through the vias, which will cause the short circuit.

    I think I can just remove the related vias, how do you think about that?

    Thanks.

    • Post Points: 20
  • Mon, Nov 12 2012 12:19 PM

    • fitz
    • Top 150 Contributor
    • Joined on Wed, Aug 4 2010
    • Kanata, Ontario
    • Posts 56
    • Points 745
    Re: short circuit problems in P & R Reply

    If there is any active circuitry on the cell row I would be very wary of deleting either of the nearest power via stacks completely.
    That may lead to static and / or  dynamic  IR drop  issues, local voltages lower than your worst case timing library will model correctly.
    Finding IR drop problems at the last minute before tape out is no fun whatsoever, believe me.

    You can use the "editPowerVia" command to selectively reduce the array size of the power via stacks in the problem areas.
    For example, reduce the via stack array from a 6x1 array to a 4x1 in localized problem areas.

    Or if you know the "full sized"  power via stack array is over kill for your technology / library / circuit
    you can globally shrink them from the start with  the addStripe option -max_via_size.


    Shawn  

    • Post Points: 5
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Started by quiet at 17 Oct 2012 01:42 AM. Topic has 5 replies.