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align the trial route estimate with nanoRoute when "double-via" requirement presents

Tongju

I have to agree that FE trial route is doing a very good job to estimate the routability in a very short time. 

 However, when the area is tight and double-via is a strict requirement, I thought the trial route tend to give too optimistic report. As a result, a routable placement by trial router  (no congestion/routing overflow reported by trial router) may end up failure in the actual nanoRoute stage. I thought that the trial route may not actually use the double vias provided in LEF file to do its job: it always apply single cut via even there is no single cut via defined inside the LEF file. Is this observation right? If it is, how can we work-around this issue? Your opinion is highly appreciated!

 Tongju

Parents

  • Hi, Kari,

     The vias used by trialRoute are same set of vias, which come from my tech LEF file. In the trialRoute results, I saw a lot of vias are shorting to other nets. But the trialRoute report the design routable:

     ---------------------------------------

    Congestion distribution:

    Remain         cntH                    cntV

    -1                    0       0.00%      10           0.02%

    0                    1        0.00%      1587        2.43%

    1                   18       0.03%      7520        11.5%

    ...

    When I tried the same placement with nanoRoute, I got thousands of shorts remainning.  However, If I add a single cut via into my LEF file (my current LEF file ONLY have double cut cut vias), then, trialRoute and nanoRoute will give me consistant result: roughly routable ( nanoRoute will finish the route with one or two shorts).

    Tongju

Reply

  • Hi, Kari,

     The vias used by trialRoute are same set of vias, which come from my tech LEF file. In the trialRoute results, I saw a lot of vias are shorting to other nets. But the trialRoute report the design routable:

     ---------------------------------------

    Congestion distribution:

    Remain         cntH                    cntV

    -1                    0       0.00%      10           0.02%

    0                    1        0.00%      1587        2.43%

    1                   18       0.03%      7520        11.5%

    ...

    When I tried the same placement with nanoRoute, I got thousands of shorts remainning.  However, If I add a single cut via into my LEF file (my current LEF file ONLY have double cut cut vias), then, trialRoute and nanoRoute will give me consistant result: roughly routable ( nanoRoute will finish the route with one or two shorts).

    Tongju

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