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Synchronizer Selection Guide: Interview Drills

Interview Drills for Synchronizer Selection Guide.

Interview drills

Interview Drills for Synchronizer Selection Guide focuses on crossing class coverage, incorrect pattern usage rate, waiver count. The goal is to convert issue observations into mechanism-backed closure decisions.

diagram

PROMPT
You see crossing class coverage, incorrect pattern usage rate, waiver count in Synchronizer Selection Guide. Explain root cause and signoff decision.

STRONG ANSWER
1. Names crossing/reset class and context.
2. Explains Crossing intent (level, pulse, bus, control/data coupling) determines legal synchronization topology and verification evidence.
3. Requests crossing taxonomy matrix, approved synchronizer templates, waiver policy.
4. Chooses fix/waiver/escalation with regression plan.

WEAK ANSWER
Lists tool commands or generic advice without mechanism and risk framing.

Diagram to draw on whiteboard

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

Debug tree to narrate

diagram

ROOT-CAUSE TREE — Synchronizer Selection Guide

crossing failure observed
        |
   reproducible?
     /        \
   no          yes
   |            |
stress mode   classify issue
expansion       /      |      \
            synchronizer protocol reset/reconvergence
                 |         |           |
            MTBF fit    liveness    release ordering

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

Practice this lesson