Handshake Protocols Across Domains: Interview Drills

Interview drills

Interview Drills for Handshake Protocols Across Domains focuses on req/ack completion reliability, deadlock risk, backpressure behavior. The goal is to convert issue observations into mechanism-backed closure decisions.

PROMPT
You see req/ack completion reliability, deadlock risk, backpressure behavior in Handshake Protocols Across Domains. Explain root cause and signoff decision.

STRONG ANSWER
1. Names crossing/reset class and context.
2. Explains Two-way handshakes guarantee delivery across asynchronous clocks when both request and acknowledge paths are synchronized and protocol invariants are enforced.
3. Requests handshake timing spec, assertion suite, latency histogram.
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

Req/Ack flow

SRC: req -----> DEST
SRC: <----- ack  DEST

Rules:
1) req stable until ack observed
2) req/ack each cross through synchronizer
3) no combinational loop across domains

Debug tree to narrate

ROOT-CAUSE TREE — Handshake Protocols Across Domains

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

Two-way handshakes guarantee delivery across asynchronous clocks when both request and acknowledge paths are synchronized and protocol invariants are enforced.

Metric: req/ack completion reliability, deadlock risk, backpressure behavior