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LichengGuo-UCLA
Visitor
Visitor
391 Views
Registered: ‎02-19-2021

Change physical cell equation of LUT

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Hi everyone,

I'm trying to hack the post-routing checkpoints.

Specifically, I want to move a cell to a LUT that is configured as route-through.

LichengGuo-UCLA_0-1620426106976.png

 

Once I run "place_cell XXXX SLICE_X128Y277/A6LUT", I will get the complaint that "Cannot use A6 pin since it is in use"

Somehow that this LUT is empty, but the IS_USED property is marked True.

LichengGuo-UCLA_0-1620428157205.png

 

 

It is a way to reconfigure this LUT and let me do the replacement (followed by re-routing) ?

Thanks for your help! 

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1 Solution

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driesd
Xilinx Employee
Xilinx Employee
252 Views
Registered: ‎11-28-2007

Hi Licheng

This XXXX LUT, is this the route-through LUT?

Or are you trying to move another LUT to that location where there is currently a route-through LUT?


Route-through LUTs are required to reach certain other pins inside the SLICE like CARRY or FF.

I would recommend either to choose another location for your LUT or to move the CARRY or FF. You cannot put a LUT on a LUT already used as route-through.

 

Best regards

Dries

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3 Replies
driesd
Xilinx Employee
Xilinx Employee
253 Views
Registered: ‎11-28-2007

Hi Licheng

This XXXX LUT, is this the route-through LUT?

Or are you trying to move another LUT to that location where there is currently a route-through LUT?


Route-through LUTs are required to reach certain other pins inside the SLICE like CARRY or FF.

I would recommend either to choose another location for your LUT or to move the CARRY or FF. You cannot put a LUT on a LUT already used as route-through.

 

Best regards

Dries

--------------------------------------------------------------------------------------------------------------------
Please mark the Answer as "Accept as solution" if the information provided is helpful.

Give Kudos to a post which you think is helpful and reply oriented by clicking the star next to the post.

View solution in original post

LichengGuo-UCLA
Visitor
Visitor
216 Views
Registered: ‎02-19-2021

Thanks for your explanation. So those route-through LUTs are determined after placement?

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driesd
Xilinx Employee
Xilinx Employee
183 Views
Registered: ‎11-28-2007

Yes, based on the placement of these registers/CARRY elements, a route-through LUT is used.

--------------------------------------------------------------------------------------------------------------------
Please mark the Answer as "Accept as solution" if the information provided is helpful.

Give Kudos to a post which you think is helpful and reply oriented by clicking the star next to the post.