Signoff Regression Hygiene: Design Space

Design space exploration

For Signoff Regression Hygiene, closure options trade margin, schedule, and regression risk.

Option A — conservative

• Conservative margin: helps safe signoff

• Risk: over-pessimism, area/power

• Validate with: first silicon

Option B — balanced

• Balanced derate: helps reasonable margin

• Risk: needs approval

• Validate with: mature node

Option C — aggressive ECO

• Aggressive ECO: helps fast WNS gain

• Risk: hold/SI regressions

• Validate with: late schedule

Option D — RTL restructure

• RTL restructure: helps structural fix

• Risk: schedule hit

• Validate with: chronic paths

DESIGN SPACE — Signoff Regression Hygiene
margin <-> performance <-> schedule
pick based on run-to-run WNS drift, database tag consistency, closure memo completeness on product scenarios

Design pitfalls

• ECO without regression matrix

• Constraint change without audit

Tradeoff curve

BEFORE / AFTER ECO — Signoff Regression Hygiene

WNS (ps)
  0 |                    --- target
-50 |    ● regressed
-80 |         ● before ECO
-20 |              ● after ECO
    +-------------------------------> ECO iteration
Prove setup AND hold moved safely.

STA deep dive

Debug hygiene separates senior STA leads from report readers.

Concept diagram

DEBUG ORDER

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

Metric graph

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