MMMC Debug Playbook: Worked Example

Worked example

Worked Example for MMMC Debug Playbook focuses on scenario-specific violation clusters, corner isolation time. The goal is to connect the observable symptom to timing mechanism, ownership, and regression risk.

A signoff run shows scenario-specific violation clusters, corner isolation time. 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 MMMC Debug Playbook.

Sequence under inspection

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

Corner isolation heatmap

WNS BY CORNER (mV)

        ss   tt   ff
reg2reg -80  +20  +5
hold    -12  -3   -15
io      +10  +30  +25

Cluster guides which scenario to debug first.

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 per-corner WNS heatmap, mode failure matrix, scenario replay script.

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

Did the fix work?

BEFORE / AFTER ECO — MMMC Debug Playbook

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

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