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different skew report between Astro and PrimeTime

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blueant

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astro skew report

Hello eveybody,I have a difficulty:
In one case, Astro's skew report is very good (0.2n). But We use SDF(from Astro) and SPEF(from Astro and StarRC) in PrimeTime, find the skew is very big (>0.8n), that so ATPG cannot pass.
anyone can tell me why? I should how to do?
Thanks
:cry:
 

albred

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primetime skew check

maybe there is crosstalk in your clock path.

to protect clock net from being attack by signal nets,you should route clock net solely(set the constraint of double spacing to the clock net for routing) before global route .
 

SkyHigh

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primetime to astro

Albred,

Crosstalk does not cause skew. Crosstalk causes jitter. Skew is caused by different lengths of wires from clock source to clock feed. Uneven load and parasitic capacitance presented by domains at the clock feed also causes skew.


Blueant,

Check your clock distribution tree locally in domains and globally between domains. These domains probably present different load capacitances to the clock tree, resulting skew. One or more wires carrying the clock signal might be longer than the other. I refer a domain as an individual digital block that shares the same local clock. It is the same term used in ASIC textbook written by Michael Sebestian Smith (Hawaii) and Digital System Engineering textbook written by Dally Poulton (Stanford)
 

luancao

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primetime+astro

The reported result should not have such a big depency...

What's the techology you are using?
 

blueant

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prime time report skew

Thanks for your replies.
 

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