Why ?
-- Timing engines in Astro and PrimeTime are different.
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How ?
-- If you treat PrimeTime as the sign-off STA tool, then you may need to fix those violations in Astro based on PrimeTime's violation report.
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As long as the timing engines in implementation tool and sign-off tool are different, then the correlation issue is inevitable.
Over-constrain does not always work.
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