CDC Protocol Verification: Interview Drills

Interview drills

Interview Drills for CDC Protocol Verification focuses on assertion pass rate, liveness coverage, CDC protocol bug escape rate. The goal is to convert issue observations into mechanism-backed closure decisions.

PROMPT
You see assertion pass rate, liveness coverage, CDC protocol bug escape rate in CDC Protocol Verification. Explain root cause and signoff decision.

STRONG ANSWER
1. Names crossing/reset class and context.
2. Explains CDC closure requires proving protocol safety and liveness, not only structural synchronizer presence.
3. Requests SVA package, formal liveness report, simulation stress matrix.
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

Safety + liveness

SAFETY: no duplicate / no drop
LIVENESS: every req eventually gets ack

Structural clean CDC is necessary, not sufficient.

Debug tree to narrate

ROOT-CAUSE TREE — CDC Protocol Verification

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

CDC/RDC deep dive

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

Concept diagram

PROTOCOL FLOW

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

Metric graph

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

CDC closure requires proving protocol safety and liveness, not only structural synchronizer presence.

Metric: assertion pass rate, liveness coverage, CDC protocol bug escape rate