Worked example

Worked Example for ECO Regression Matrix focuses on corners re-run, new violations introduced, signoff delta. The goal is to connect the observable symptom to timing mechanism, ownership, and regression risk.

A signoff run shows corners re-run, new violations introduced, signoff delta. The first review mistake is to blame implementation without checking constraints. A better review starts by pinning one critical path, proving where slack was lost, and checking whether the SDC rule is correct for ECO Regression Matrix.

Sequence under inspection

TIMING PATH — ECO Regression Matrix

launch FF --logic stages--> capture FF
     |                           |
  launch clock                capture clock
     |                           |
  required: arrival < capture_edge - setup
  metric: corners re-run, new violations introduced, signoff delta

Post-ECO regression

ECO REGRESSION CHECKLIST
[ ] all MMMC scenarios
[ ] SI re-run
[ ] power/leakage delta
[ ] equivalence / LVS if logical ECO
[ ] signoff memo updated

1. Capture report_timing and the relevant SDC excerpt.

2. Tag corner, mode, view, and path group.

3. Find the first cell or net that dominates critical delay.

4. Compare against regression manifest, corner comparison table, signoff approval.

5. Choose one reversible ECO and write the regression matrix before editing netlist or constraints.

Did the fix work?

BEFORE / AFTER ECO — ECO Regression Matrix

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

STA deep dive

ECO without regression is a coin flip.

Concept diagram

ECO LOOP

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

Metric graph

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

Every ECO must re-run the agreed MMMC matrix plus SI; regression hygiene prevents shipping a fix that breaks another corner.

Metric: corners re-run, new violations introduced, signoff delta