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 Question of cell placement in P&R (SOC encounter) 

Last post Tue, Oct 16 2012 9:46 AM by bjbit. 2 replies.
Started by bjbit 15 Oct 2012 01:29 PM. Topic has 2 replies and 1116 views
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  • Mon, Oct 15 2012 1:29 PM

    • bjbit
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    Question of cell placement in P&R (SOC encounter) Reply

    Hi,

    When I try to place standard cells into the floorplan, I notice that the cells are not averagely distributed, no matter how I set the utilization percentage. Please check out the attacked picture. I even tried the utilization of 200%, and there still be some space forced to be empty. Conversely, the placed cells are heavily overlapping with each other in the rest area. I understand that a common setting of 70% utilization has no overlapping issue. But I am confusing with the exist of the empty wasted space. Is there anything I missed? Thanks.

    Best regards, 


    • Post Points: 20
  • Mon, Oct 15 2012 1:54 PM

    • Scrivner
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    Re: Question of cell placement in P&R (SOC encounter) Reply

    I'm not in expert in the placement algorithm but the I think the placer will cluster cells from modules that have alot of connectivity or  timing critical paths in order to reduce parasitics or congestion during routing. This is why it will create cell clusters and then leave parts of the floorplan unused. When utilization is over 100%, strange things happen (placer gets confused?) so don't make any assumptions from placement results when the design utilization is over 100%.

     Try using the option: setPlaceMode -modulePadding <module name(s)> <padding factor>

    This is what I typicaly use this to spread out cell placements.

    • Post Points: 20
  • Tue, Oct 16 2012 9:46 AM

    • bjbit
    • Top 100 Contributor
    • Joined on Tue, Mar 6 2012
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    Re: Question of cell placement in P&R (SOC encounter) Reply

    Thanks, Scrivner. Setting padding factor seems not spread out every cell to fill out the space. But I notice that 90% utilization gives me a fine placement with small space. I may try more on other settings.

    Best regards, 

    • Post Points: 5
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Started by bjbit at 15 Oct 2012 01:29 PM. Topic has 2 replies.