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STA Mastery · All levels

Scenario: MMMC Storm

A library refresh changes hold margins on SS corner only. Synthesis says timing is fine; signoff STA shows new hold violations on clock-gating paths.

Scenario

A library refresh changes hold margins on SS corner only. Synthesis says timing is fine; signoff STA shows new hold violations on clock-gating paths.

diagram
OBSERVED METRIC
WNS fails on 3 corners after lib update but passes on implementation view

45-MINUTE INTERVIEW FLOW
0-5: clarify corner/mode/view and path group
5-15: read critical path and constraints
15-25: classify constraint vs view vs real path
25-35: propose ECO order (setup/hold/SI)
35-45: state MMMC regression and signoff criteria

Common pitfalls

  • Re-run only typical corner

  • Ignore lib mapping diff

  • Blame PD without scenario isolation

Scenario debrief

Score: corner/mode, path group, constraint check, ECO, regression.

diagram
constraints -> graph -> slack
diagram
WNS trend

Debrief prompts

  1. Which scenario failed first?

  2. Setup, hold, or both?

  3. What regression did you mandate?

Key takeaways

  • State corner, mode, view, and database tag with every slack claim.

  • Run setup and hold plus MMMC regression after every ECO.

Common pitfalls

  • Comparing STA runs with different SPEF or SDC tags.

  • Broad false_path to green-wash violations.

  • Setup-only ECO without hold check.

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