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Library Set & Opcond Mapping: Comparison Matrix

Comparison Matrix for Library Set & Opcond Mapping.

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 — Library Set & Opcond Mapping

+-------------------+------------------------+--------------------------+-------------------------+
| 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

Each corner binds liberty libraries and operating conditions; wrong mapping makes every slack number meaningless.

Metric: library mismatch count, opcond alignment errors, derate mapping gaps

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