Two-Flop Synchronizers in Practice: Review Checklist

Review checklist

Review Checklist for Two-Flop Synchronizers in Practice focuses on single-bit CDC clean rate, pulse capture reliability, latency cycles. The goal is to convert issue observations into mechanism-backed closure decisions.

• Crossing and reset intent are explicitly classified.

• Protocol assumptions are documented and checked.

• Critical issues have owners and dates.

• Waivers include mechanism, containment, and expiry.

• Regression matrix includes stress and milestone modes.

• Owners signed: RTL owner, CDC owner, verification owner.

Signoff ownership

OWNERSHIP MAP — Two-Flop Synchronizers in Practice

artifact                  owner
----------------------    -------------------------
design intent           RTL owner
verification evidence   CDC owner
signoff decision        verification owner

Every open CDC/RDC issue needs one accountable owner before waiver or fix.

CDC/RDC deep dive

Metastability is managed risk, not eliminated risk.

Concept diagram

METASTABILITY FLOW

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

Metric graph

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

A two-flop chain lowers metastability propagation risk for level signals, but only when source assumptions, pulse width, and destination sampling are respected.

Metric: single-bit CDC clean rate, pulse capture reliability, latency cycles