Scenario: Retiming Debate: Mechanism

Mechanism to understand

Mechanism for Scenario: Retiming Debate focuses on frequency target miss versus latency and verification budget. The goal is to connect observed QoR movement to mechanism, ownership, and regression risk.

Retiming debate evaluates whether register movement is safer than RTL pipeline edits under schedule and formal constraints. Treat synthesis as a contract: constraints + transforms + reports must agree.

• Identify which lane moved first: timing, area, power, or runtime.

• Identify whether drift is input, transform, or correlation related.

• Identify owner before applying any ECO.

Flow model

SYNTHESIS FLOW — Scenario: Retiming Debate

RTL + constraints
      |
      v
elaboration + checks
      |
      v
mapping + optimization
      |
      v
QoR reports (timing/area/power)
      |
      v
incremental ECO + regression

Primary metric: frequency target miss versus latency and verification budget

Retiming debate matrix

retime now?
benefit: Fmax
cost: formal + latency + schedule
decision by risk budget

Layer responsibilities

SYNTHESIS OWNERSHIP LAYERS — Scenario: Retiming Debate

layer               owns                          failure mode
----------------    ---------------------------   -------------------------
constraints         clocks/exceptions/policy      fake QoR optimism
mapping             cell choices/structure        depth/fanout regressions
optimization        timing/power tradeoffs        one-metric overfitting
physical-aware      topo/congestion estimates     handoff delta surprises
closure             ECO order/regression          fixes break other corners

Synthesis deep dive

Interview readiness comes from repeatable QoR reasoning under pressure.

Concept diagram

INTERVIEW ANSWER SHAPE

context -> metric -> mechanism -> fix -> regression -> ownership

Metric graph

PANEL SCORING

clarity      ███████
mechanism    ██████
regression   █████

Reports and artifacts

• mock scorecard

• scenario debrief

• Q&A coverage

• framework adherence

Mini case study

Candidate improved by replacing tool-command answers with evidence-driven closure narratives.

Debug branches

• State assumptions first

• Defend option tradeoffs

• Close with rollback/regression

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.

Mechanism deep dive

Retiming debate evaluates whether register movement is safer than RTL pipeline edits under schedule and formal constraints.