CDC / RDC · All levels

CDC Protocols & Handshakes: Tricky Q&A

Senior interview and review questions for CDC Protocols & Handshakes.

Section Q&A bank

Use these drills after completing all topics in CDC Protocols & Handshakes. Answer with crossing class, mechanism, risk, evidence, owner, and signoff decision.

Why use async FIFO over handshake?

diagram

[INT][CDC-RDC][CDC-PROTOCOLS]

Q: Why use async FIFO over handshake?

A:
When throughput decoupling and burst absorption are required; handshake is lower area but lower throughput for sustained traffic.

FOLLOW-UP TRAP: Choosing FIFO without pointer proof.

What proves handshake correctness?

diagram

[INT][CDC-RDC][CDC-PROTOCOLS]

Q: What proves handshake correctness?

A:
Safety and liveness assertions: no drop/duplication and eventual ack under legal environment assumptions.

FOLLOW-UP TRAP: Relying on random simulation pass only.

How do pulse crossings fail?

diagram

[INT][CDC-RDC][CDC-PROTOCOLS]

Q: How do pulse crossings fail?

A:
Pulse width can be shorter than destination sampling period, causing misses or duplicates without toggle/ack design.

FOLLOW-UP TRAP: Ignoring frequency ratio corners.

Q&A drill guide

diagram

INTENT -> FAILURE MODE -> EVIDENCE -> FIX/WAIVER -> REGRESSION

Sketch while answering

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PROTOCOL FLOW

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

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.

Practice this lesson