Handshake Protocols Across Domains: Expanded Case Study

Extended case study

Milestone review flags req/ack completion reliability, deadlock risk, backpressure behavior around Handshake Protocols Across Domains.

Background

Team believed crossings were stable until stress mode exposed intermittent anomalies.

Symptoms observed

• req/ack completion reliability, deadlock risk, backpressure behavior regression

• Mismatch between structural report and dynamic behavior

• Waiver debate under schedule pressure

Investigation timeline

1. Freeze design, reset, and tool configuration tags.

2. Reproduce failing scenario with minimized stimulus.

3. Map path/protocol/reset dependencies.

4. Classify root cause and containment options.

5. Execute minimal safe fix.

6. Run stress regression and review board.

Root cause

Root cause links to Handshake Protocols Across Domains: Two-way handshakes guarantee delivery across asynchronous clocks when both request and acknowledge paths are synchronized and protocol invariants are enforced.

Fix and validation

• Targeted RTL/protocol/reset correction

• Evidence refresh

• Signoff board decision

Lessons learned

• Treat waivers as temporary risk contracts

• Track owner and expiry

• Regression before closure

CASE STUDY — Handshake Protocols Across Domains
critical issues before / after / signoff

Crossing sequence under stress

CROSSING FLOW — Handshake Protocols Across Domains

source clock domain -> launch signal -> crossing structure -> destination sample
      |                    |                 |                    |
   source FF           protocol           sync / fifo         destination FF

Key metric: req/ack completion reliability, deadlock risk, backpressure behavior

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