Synthesis & Logic Optimization · All levels

Clock-Gating Inference: Step-by-Step Walkthrough

Step-by-Step Walkthrough for Clock-Gating Inference.

Step-by-step analysis walkthrough

Use when you own Clock-Gating Inference in a synthesis closure review.

Confirm exact run context (RTL/SDC/lib/switch set).
Open section QoR dashboard and identify first drift.
Inspect topic-level report for mechanism evidence.
Determine owner and candidate reversible action.
Apply one change only; avoid bundled fixes.
Run full timing/area/power checks.
Validate side effects on neighboring path groups.
Publish memo with outcome and residual risk.

Artifacts to collect

clock-gating report, enable-condition review, power comparison
QoR dashboard
run manifest
constraint diff
regression matrix

Decision memo template

diagram

SYNTHESIS DECISION MEMO — Clock-Gating Inference
run context:
observed metric:
hypothesis:
fix:
regression:
owners: synthesis owner, power owner, verification owner

Reference visuals

Clock-gating insertion loop

diagram

RTL enable intent
      |
      v
gating inference rules
      |
      v
insert ICG cells + checks
      |
      v
power delta + gating-safe verification

Synthesis deep dive

Constraint hygiene determines whether synthesis QoR is trustworthy.

Concept diagram

diagram

CONSTRAINT FLOW

RTL intent -> synthesis SDC -> compile checks -> QoR dashboard -> review gate

Metric graph

diagram

QOR HEALTH

constraint lint pass   ███████████████
unconstrained count    ███
policy violations      ██

Reports and artifacts

compile QoR
unconstrained endpoints
constraint lint
policy audit log

Mini case study

Nightly WNS improved but unconstrained paths jumped; strict SDC lint restored true QoR picture.

Debug branches

Diff SDC first
Audit dont_touch scope
Track unconstrained trend weekly

Senior review question

Ask: what evidence proves this QoR move is real and stable?

Key takeaways

State exact run context (RTL, SDC, libs, switches) with every QoR claim.
Re-run timing, area, and power regressions after each synthesis ECO.

Common pitfalls

Comparing runs with mismatched constraints or library views.
Timing-only fixes that violate power or area budgets.
Skipping equivalence checks after structural changes.

Principal synthesis review addendum

Inference quality depends on RTL style and constraints; wrong enable semantics or exclusion policy causes either missed savings or unsafe gating.

Metric: clock-gating insertion rate, gating check violations, clock power delta

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