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Setup / Hold Closure Order: Pitfalls & Red Flags

Pitfalls & Red Flags for Setup / Hold Closure Order.

Pitfalls and red flags

Pitfalls & Red Flags for Setup / Hold Closure Order focuses on setup WNS, hold WNS, simultaneous violation count. The goal is to connect the observable symptom to timing mechanism, ownership, and regression risk.

  • A path looks clean in one view but fails in signoff SPEF.

  • The SDC allows behavior that the implementation team assumed was illegal.

  • A generated_clock definition shifts capture edge silently.

  • Hold fails on short paths after setup-focused ECO.

  • The fix improves one corner but regresses another MMMC scenario.

Layer responsibility check

diagram
STA OWNERSHIP LAYERS — Setup / Hold Closure Order

layer              owns                         failure mode
----------------   --------------------------   ---------------------
constraints        clocks, IO, exceptions       false violations
implementation     cells, nets, placement       real path delay
extraction         SPEF/RC corners              view mismatch
signoff policy     derate, MMMC matrix          margin disputes
closure           ECO order, regression        fix breaks other corner

STA deep dive

ECO without regression is a coin flip.

Concept diagram

diagram
ECO LOOP

failing path -> fix -> setup check -> hold check -> SI -> MMMC matrix

Metric graph

diagram
ECO PROGRESS

WNS
 0 |              o target
-50|        o
-100|   o baseline
    +-----------------> ECO #

Reports and artifacts

  • pre/post WNS

  • hold delta

  • leakage delta

  • ECO ticket log

Mini case study

48-hour tapeout crunch: VT swap fixed setup; hold fixed with route on short path — order mattered.

Debug branches

  • Never ship setup-only proof

  • Logical ECO needs equivalence

Senior review question

Ask: what corner/mode/view proves this topic is closed or failing?

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.

Principal STA review addendum

Setup and hold compete through delay changes; closure order and ECO type must avoid fixing one at the expense of the other.

Metric: setup WNS, hold WNS, simultaneous violation count

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