Library Set & Opcond Mapping: Mechanism

Mechanism to understand

Mechanism 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.

Each corner binds liberty libraries and operating conditions; wrong mapping makes every slack number meaningless. Think of STA as a signed contract between constraints, parasitics, and implementation — slack is the measurable outcome.

• Identify launch and capture clocks on the failing path.

• Identify path group: reg2reg, in2reg, reg2out, or async.

• Identify whether setup, hold, or both fail in the scenario.

Layered view

STA CLOSURE FLOW — Library Set & Opcond Mapping

constraints (SDC)
        |
        v
timing graph (cell + net delays)
        |
        v
MMMC scenarios (corner x mode x view)
        |
        v
variation + SI adjustments
        |
        v
slack (WNS/TNS) -> ECO -> regression

Debug rule: always state corner, mode, view, and database tag with slack.

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.

Layer responsibilities

STA OWNERSHIP LAYERS — Library Set & Opcond Mapping

layer              owns                         failure mode
----------------   --------------------------   ---------------------
constraints        clocks, IO, exceptions       false violations
implementation     cells, nets, placement       real path delay
extraction         SPEF/RC corners              view mismatch
signoff policy     derate, MMMC matrix          margin disputes
closure           ECO order, regression        fix breaks other corner

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.

Mechanism deep dive

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