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CDC / RDC · All levels

Pulse Synchronizers: Step-by-Step Walkthrough

Step-by-Step Walkthrough for Pulse Synchronizers.

Step-by-step analysis walkthrough

Use this sequence when owning Pulse Synchronizers in a signoff review.

  1. Inspect warning class and severity.

  2. Trace crossing endpoints and domains.

  3. Check protocol/reset assumptions against spec.

  4. Review synchronizer or FIFO implementation detail.

  5. Run focused assertion or formal check.

  6. Draft fix options with risk and schedule impact.

  7. Execute regression and publish closure memo.

Artifacts to collect

  • pulse width assumptions, toggle synchronizer checks, simulation traces

  • crossing inventory

  • waiver board notes

  • regression report

Decision memo template

diagram
CDC/RDC DECISION MEMO — Pulse Synchronizers
risk class:
mechanism:
evidence:
fix/waiver:
owners: RTL owner, CDC owner, DV owner

Reference visuals

Pulse-safe transfer

diagram
short pulse in src domain
   -> toggle bit
   -> sync toggle into dest
   -> edge detect in dest

Avoid pulse loss when destination clock is slower.

CDC/RDC deep dive

Protocol correctness is the bridge between structural clean and functional safe.

Concept diagram

diagram
PROTOCOL FLOW

intent -> transport protocol -> synchronization -> destination acceptance

Metric graph

diagram
PROTOCOL ISSUE BURNDOWN

open issues: 20 -> 11 -> 5 -> 0

Reports and artifacts

  • FIFO pointer proofs

  • req/ack liveness

  • pulse miss checks

  • protocol assertions

Mini case study

Async FIFO empty/full logic looked correct until gray decode mismatch appeared during reset overlap.

Debug branches

  • Pointer sync audit

  • formal liveness checks

  • reset interaction review

Senior review question

Ask: what evidence proves this risk is closed for silicon, not just tool-clean?

Key takeaways

  • State crossing class, assumptions, and owner with every issue.

  • Run structural and dynamic regressions after each fix.

Common pitfalls

  • Treating all warnings as equivalent risk.

  • Waiving issues without containment evidence.

  • Skipping reset and reconvergence stress after CDC fixes.

Principal CDC/RDC review addendum

Pulse crossings require width expansion, toggle encoding, or ack-backed transport because short pulses can vanish between destination sampling edges.

Metric: pulse miss rate, minimum pulse width margin, duplication events

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