CDC / RDC · All levels

Scenario: Metastability Bug: Debug Playbook

Debug Playbook for Scenario: Metastability Bug.

Debug playbook

Debug Playbook for Scenario: Metastability Bug focuses on root-cause depth, containment plan clarity, debug sequencing. The goal is to convert issue observations into mechanism-backed closure decisions.

CDC/RDC debug is about finding the earliest violated assumption. Start with intent and context before touching low-level signal traces.

Root-cause tree

diagram

ROOT-CAUSE TREE — Scenario: Metastability Bug

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

Freeze RTL/config/tool tags for reproducibility.
Reproduce in smallest mode/reset/traffic scenario.
Classify mechanism: synchronizer, protocol, reset, reconvergence, or governance.
Collect one decisive artifact that proves the class.
Pick minimal fix or bounded waiver.
Run targeted and full-regression matrices before closure.

Review memo template

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STAFF CDC/RDC REVIEW MEMO — CDC/RDC Interview Prep / Scenario: Metastability Bug

1. Symptom
   - Failing metric: root-cause depth, containment plan clarity, debug sequencing
   - Context: <mode, traffic, reset state, corner>
   - Risk class: <critical/high/medium/low>
   - Database tags: <rtl, config, assertions, tool setup>

2. Mechanism hypothesis
   - Primary mechanism: A rare metastability escape tests whether the engineer can distinguish random symptom from deterministic crossing design flaws.
   - Competing hypothesis: <false warning / protocol bug / reset order / reconvergence>
   - Missing evidence: <assertion, waveform, formal proof, stress replay>

3. Proposed action
   - Minimal reversible change: <sync/protocol/reset/waiver decision>
   - Expected metric movement: <critical count delta>
   - Regression risk: throughput, boot, latency, mode interaction

4. Signoff
   - Re-run artifact: failure report, crossing path analysis, fix validation plan
   - Required owners: candidate, CDC owner, DV lead
   - Final decision: fix, bounded waiver, or escalate

Scenario debrief

Score each response on mechanism clarity, evidence quality, and signoff decision discipline.

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INTERVIEW FLOW

classify -> explain mechanism -> propose fix -> state regression

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PRACTICE SCORE

session1 62%
session2 78%
session3 89%

Debrief prompts

Which crossing class or reset dependency failed first?
What evidence changed your decision?
Fix, waive, or escalate and why?

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