MMMC Debug Playbook: Expanded Case Study

Extended case study

Signoff review: scenario-specific violation clusters, corner isolation time fails after an apparently minor change affecting MMMC Debug Playbook.

Background

Team had closure last week on full MMMC matrix. New run shows regression clustered in one path group.

Symptoms observed

• scenario-specific violation clusters, corner isolation time regression

• Disagreement between synth and STA WNS

• Hold violations after setup ECO

Investigation timeline

1. Hour 0: freeze netlist, SDC, SPEF, lib tags

2. Hour 1: diff constraints and run manifest

3. Hour 2: isolate corner/mode that fails

4. Hour 3: read worst path — cell vs net, clocks

5. Hour 4: classify root cause

6. Hour 5: minimal ECO or SDC fix

7. Hour 6: full regression + signoff memo

Root cause

Root cause tied to MMMC Debug Playbook: MMMC failures cluster by corner, mode, or library; triage isolates the scenario before touching RTL or layout.

Fix and validation

• Bounded ECO or audited SDC change

• Re-run per-corner WNS heatmap, mode failure matrix, scenario replay script

• Full MMMC + SI regression

Lessons learned

• Tag every run

• Diff constraints before blaming PD

• Setup and hold together

CASE STUDY — MMMC Debug Playbook
baseline WNS / regressed WNS / post-fix WNS

Sequence under stress

TIMING PATH — MMMC Debug Playbook

launch FF --logic stages--> capture FF
     |                           |
  launch clock                capture clock
     |                           |
  required: arrival < capture_edge - setup
  metric: scenario-specific violation clusters, corner isolation time

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

MMMC failures cluster by corner, mode, or library; triage isolates the scenario before touching RTL or layout.

Metric: scenario-specific violation clusters, corner isolation time