DenseChip

STA Mastery · All levels

Signoff Regression Hygiene: Step-by-Step Walkthrough

Step-by-Step Walkthrough for Signoff Regression Hygiene.

Step-by-step analysis walkthrough

Use when you own Signoff Regression Hygiene in a timing war room.

  1. Open signoff scenario list — note worst WNS corner.

  2. report_timing -max/-min on failing group.

  3. Trace launch and capture clocks on critical path.

  4. Check exceptions and generated clocks on path.

  5. Break down cell vs net delay.

  6. Compare implementation vs signoff view if delta suspicious.

  7. Assign owner: RTL, synth, PD, CTS, SI.

  8. Propose ECO with hold/SI check plan.

  9. Run regression matrix.

  10. Update closure dashboard and memo.

Artifacts to collect

  • run manifest, git/DB tag log, signoff checklist

  • SDC file

  • SPEF tag

  • MMMC scenario list

  • ECO ticket

Decision memo template

diagram
STA DECISION MEMO — Signoff Regression Hygiene
corner/mode:
WNS/TNS:
hypothesis:
ECO:
regression:
owners: STA lead, CAD owner, program management

Reference visuals

Run manifest

diagram
STA RUN MANIFEST
design: chip_top tag v2.4.1
sdc:    constraints_v18.git
spef:   cworst_v3
libs:   ss_125 / ff_m40 / ...
tool:   PrimeTime Q-2020.03
scenarios: 36 (full matrix)

STA deep dive

Debug hygiene separates senior STA leads from report readers.

Concept diagram

diagram
DEBUG ORDER

1. same tags?  2. constraints?  3. view?  4. real path?  5. ECO

Metric graph

diagram
ROOT CAUSE MIX (typical)

constraint bugs  ████████  35%
view mismatch    ██████    25%
real path        ██████    25%
methodology      ████      15%

Reports and artifacts

  • run manifest

  • SDC diff

  • SPEF tag

  • scenario isolation

Mini case study

Mystery regression: SPEF corner tag typo in run script — not a design bug.

Debug branches

  • Manifest every run

  • War room by path group

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

Signoff quality depends on reproducible runs: same lib, SPEF, SDC, scenarios, and tool versions — tagged and archived.

Metric: run-to-run WNS drift, database tag consistency, closure memo completeness

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