DenseChip

CDC / RDC · All levels

Synchronizer Selection Guide: Step-by-Step Walkthrough

Step-by-Step Walkthrough for Synchronizer Selection Guide.

Step-by-step analysis walkthrough

Use this sequence when owning Synchronizer Selection Guide 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

  • crossing taxonomy matrix, approved synchronizer templates, waiver policy

  • crossing inventory

  • waiver board notes

  • regression report

Decision memo template

diagram
CDC/RDC DECISION MEMO — Synchronizer Selection Guide
risk class:
mechanism:
evidence:
fix/waiver:
owners: CDC lead, methodology owner, design lead

Reference visuals

Pattern selection map

diagram
Crossing type -> Recommended structure

single-bit level   -> 2FF / 3FF sync
single-bit pulse   -> toggle/ack pulse sync
multi-bit payload  -> async FIFO or handshake bundle
status flags       -> gray pointer or token

CDC/RDC deep dive

Metastability is managed risk, not eliminated risk.

Concept diagram

diagram
METASTABILITY FLOW

async event -> first sample may metastabilize
 -> settle window
 -> downstream sample confidence

Metric graph

diagram
MTBF TREND

target MTBF ---------
current design   ____/

Reports and artifacts

  • MTBF assumptions

  • synchronizer inventory

  • crossing class summary

  • critical waivers

Mini case study

Pulse sync chosen for a level signal caused intermittent stuck state under voltage stress.

Debug branches

  • Validate crossing class first

  • Check pulse width assumptions

  • Audit synchronizer template usage

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

Crossing intent (level, pulse, bus, control/data coupling) determines legal synchronization topology and verification evidence.

Metric: crossing class coverage, incorrect pattern usage rate, waiver count

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