Signoff vs Implementation Views: Inputs & Outputs

Inputs and outputs contract

Inputs & Outputs for Signoff vs Implementation Views focuses on view delta WNS, parasitic corner mismatch, SPEF vs signoff RC gap. The goal is to connect the observable symptom to timing mechanism, ownership, and regression risk.

Treat these as a signed interface contract. Ambiguity here is the single biggest source of wasted integration weeks, because two teams debug against different assumptions.

INPUTS
  - SDC (clocks, IO delays, exceptions)
  - Liberty libraries per corner
  - SPEF/parasitics and RC corner
  - MMMC scenario definition

OUTPUTS
  - WNS/TNS reports per scenario
  - path group summaries
  - constraint audit / waiver log
  - signoff closure memo

Timing path sequence

TIMING PATH — Signoff vs Implementation Views

launch FF --logic stages--> capture FF
     |                           |
  launch clock                capture clock
     |                           |
  required: arrival < capture_edge - setup
  metric: view delta WNS, parasitic corner mismatch, SPEF vs signoff RC gap

Ownership map

OWNERSHIP MAP — Signoff vs Implementation Views

artifact              owner
----------------      -----------------
timing report       STA lead
SDC/constraint      PD owner
implementation      extraction owner

Every WNS cluster needs a named owner before ECO.

STA deep dive

Signoff WNS is the minimum across the full scenario matrix.

Concept diagram

MMMC

corners (ss/tt/ff) x modes (func/test) x views (signoff RC)
= scenario set -> min(WNS) is signoff

Metric graph

WNS HEATMAP BY CORNER

        ss    tt    ff
setup  -80   +10   +5
hold   -15   -2    -8

Reports and artifacts

• per-corner WNS

• mode summary

• lib map audit

• view delta

Mini case study

Passed TT typical but failed SS hold — signoff matrix was incomplete; added low-voltage mode.

Debug branches

• Isolate failing scenario first

• Never compare unlike SPEF tags

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

Implementation and signoff use different parasitic corners and analysis views; comparing them without mapping causes false panic or false confidence.

Metric: view delta WNS, parasitic corner mismatch, SPEF vs signoff RC gap