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Corner / Mode Matrix Design: Comparison Matrix

Comparison Matrix for Corner / Mode Matrix Design.

Comparison matrix

Scenario pruning trades runtime against silicon risk.

diagram
+------------------+----------------+----------------+----------------+
| Approach         | Strength       | Weakness       | Best when      |
+------------------+----------------+----------------+----------------+
| Conservative     | safe           | slow closure   | risk-averse    |
| Balanced         | practical      | needs discipline | production     |
| Aggressive       | fast           | regression risk | tapeout crunch |
| RTL change       | structural     | long loop      | architectural  |
+------------------+----------------+----------------+----------------+

When to choose each approach

  • Match approach to schedule and silicon risk

Interview traps

  • One-size ECO playbook

  • Ignoring hold

Evidence comparison

diagram
STA EVIDENCE MATRIX — Corner / Mode Matrix Design

+-------------------+------------------------+--------------------------+-------------------------+
| Evidence           | Tells you              | Does not prove           | Next action             |
+-------------------+------------------------+--------------------------+-------------------------+
| report_timing      | critical path slack    | root cause class         | cell vs net split       |
| clock report       | clock reachability     | path delay               | fix generated_clock     |
| SDC diff           | constraint change      | physical delay           | re-run all scenarios    |
| SPEF tag compare   | parasitic view         | constraint quality       | isolate view mismatch   |
| MMMC dashboard     | worst scenario         | single-path fix          | assign path group owner |
+-------------------+------------------------+--------------------------+-------------------------+

STA deep dive

Signoff WNS is the minimum across the full scenario matrix.

Concept diagram

diagram
MMMC

corners (ss/tt/ff) x modes (func/test) x views (signoff RC)
= scenario set -> min(WNS) is signoff

Metric graph

diagram
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 runs STA across PVT corners and functional modes; the matrix must cover real silicon without exploding runtime.

Metric: corner coverage completeness, mode cross-product size, signoff WNS per scenario

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