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Honored Contributor I

Anyone had fitter doing bad job between partition boundaries?



I'm working on some LL+Design Partition so I can get faster design cycles and help the design to close timing easier. 

so the structure I have is like this 

+top (logic locked) 

-partition 1 (child logic lock region) 

-partition 2 (child logic lock region) 

the two child logic lock region are far away from each other so I have buffers instantiated on top level. 

After building the design, I found that the buffer gonna be pulled to one of the LL regions. say from partition 1 to buffer -300ps slack but from buffer to partition 2 is like 4000ps slack. 


Do you guys know if there is any special optimization you can turn on to solve this problem? 

Thank you for all kinds of suggestions. 



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Honored Contributor I

First thing you should try is turning off all LL regions. See what the Fitter gives you with just design partitions. Adding LL regions limits what placement the Fitter can perform. And you may not need those buffers. 


If you must do this floorplanning, put the buffers in their own separate level of the hierarchy and set the LL regions to be reserved. That way, the Fitter won't put any outside logic in the regions so it will get placed in the middle between the regions. 


But try your design without floorplanning and see what you get.