Synthesis & Logic Optimization · All levels

Retiming Fundamentals: Step-by-Step Walkthrough

Step-by-Step Walkthrough for Retiming Fundamentals.

Step-by-step analysis walkthrough

Use when you own Retiming Fundamentals 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

retiming report, stage-depth histogram, equivalence log
QoR dashboard
run manifest
constraint diff
regression matrix

Decision memo template

diagram

SYNTHESIS DECISION MEMO — Retiming Fundamentals
run context:
observed metric:
hypothesis:
fix:
regression:
owners: synthesis owner, formal owner, STA owner

Reference visuals

Retiming move

diagram

FF -> combinational -> FF
can become
comb -> FF -> comb -> FF

Goal: rebalance stage delay.

Synthesis deep dive

Datapath and retiming gains are only real if formal and timing remain clean.

Concept diagram

diagram

DATAPATH + RETIME

operator inference -> stage balancing -> formal proof -> QoR validation

Metric graph

diagram

FREQUENCY VS LATENCY

Fmax gain   ████████
latency cost ████

Reports and artifacts

retiming report
datapath inference log
equivalence status
latency impact sheet

Mini case study

Retiming met frequency target, but missing formal hooks delayed closure by two days.

Debug branches

Check retime blockers
Formal first for aggressive moves
Compare with pipeline option

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

Retiming moves registers across combinational logic to rebalance stage delay while preserving functionality under reset and enable constraints.

Metric: retimed register count, critical path depth change, equivalence pass rate

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