Library Set & Opcond Mapping: Worked Example

Worked example

Worked Example for Library Set & Opcond Mapping focuses on library mismatch count, opcond alignment errors, derate mapping gaps. The goal is to connect the observable symptom to timing mechanism, ownership, and regression risk.

A signoff run shows library mismatch count, opcond alignment errors, derate mapping gaps. 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 Library Set & Opcond Mapping.

Sequence under inspection

TIMING PATH — Library Set & Opcond Mapping

launch FF --logic stages--> capture FF
     |                           |
  launch clock                capture clock
     |                           |
  required: arrival < capture_edge - setup
  metric: library mismatch count, opcond alignment errors, derate mapping gaps

Corner to library mapping

CORNER ss_0p72v_125c
  -> opcond: ss_125c_0p72v
  -> lib: stdcell_ss_125c.lib
  -> rc: cworst_RC

Wrong lib at corner -> all slack invalid.

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 library configuration report, .lib corner map, opcond audit.

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

Did the fix work?

BEFORE / AFTER ECO — Library Set & Opcond Mapping

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

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