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Worst negative slack increases during post-CTS

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inputoutput

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I am doing a post-CTS timing optimization in Encounter. During the optimization the summary report is something as follows:

WNS (ns) -3.751
TNS (ns) -26643.7
Violating Paths: 21986
All Paths: 67386

However, after optimization is complete, timing actually gets much worse:

WNS (ns) -23.290
TNS (ns) -52498
Violating Paths: 20655
All Paths: 67306

I don't think this result is at all realistic. What could be the problem here?
 

inputoutput said:
I am doing a post-CTS timing optimization in Encounter. During the optimization the summary report is something as follows:

WNS (ns) -3.751
TNS (ns) -26643.7
Violating Paths: 21986
All Paths: 67386

However, after optimization is complete, timing actually gets much worse:

WNS (ns) -23.290
TNS (ns) -52498
Violating Paths: 20655
All Paths: 67306

I don't think this result is at all realistic. What could be the problem here?
Click to expand...

Do you have multiple corners? Sometimes the summary is based on one corner/mode, not on all the views.
 

ThisIsNotSam said:
Do you have multiple corners? Sometimes the summary is based on one corner/mode, not on all the views.
Click to expand...

No, it's just one corner. I'm getting lots of violations during nanoroute though, I don't know if that plays a role...
 

inputoutput said:
No, it's just one corner. I'm getting lots of violations during nanoroute though, I don't know if that plays a role...
Click to expand...

It does. If nanoroute fails, it will still keep a partial solution. This solution can have loops, unconnected wires, all sorts of weird shapes. Any timing optimisation applied to it is pointless.
 

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