Timing-Driven Synthesis: Step-by-Step Walkthrough

Step-by-step analysis walkthrough

Use when you own Timing-Driven Synthesis in a synthesis closure review.

1. Confirm exact run context (RTL/SDC/lib/switch set).

2. Open section QoR dashboard and identify first drift.

3. Inspect topic-level report for mechanism evidence.

4. Determine owner and candidate reversible action.

5. Apply one change only; avoid bundled fixes.

6. Run full timing/area/power checks.

7. Validate side effects on neighboring path groups.

8. Publish memo with outcome and residual risk.

Artifacts to collect

• critical range report, path-group WNS report, effort histogram

• QoR dashboard

• run manifest

• constraint diff

• regression matrix

Decision memo template

SYNTHESIS DECISION MEMO — Timing-Driven Synthesis
run context:
observed metric:
hypothesis:
fix:
regression:
owners: synthesis lead, STA owner

Reference visuals

Timing-driven effort allocation

path groups ranked by slack
      |
      v
high effort on critical groups
medium effort on near-critical
low effort elsewhere

Synthesis deep dive

Mapping converts logic intent into real PPA outcomes.

Concept diagram

MAPPING LOOP

boolean net -> library mapping -> optimization -> report and iterate

Metric graph

MAPPING IMPACT

depth reduction   ███████
fanout cleanup    █████
runtime overhead  ███

Reports and artifacts

• mapping summary

• critical path cell list

• fanout/slew report

• library coverage

Mini case study

Cell-heavy critical path improved after restructuring, while blanket buffering had worsened power.

Debug branches

• Depth issue -> structure

• Fanout issue -> buffers

• Library mismatch -> view audit

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

Timing-driven compile focuses optimization where slack is most constrained, balancing global QoR instead of over-optimizing non-critical logic.

Metric: critical path WNS, violating endpoint count, compile effort distribution