Reconvergence Analysis: Interview Drills

Interview drills

Interview Drills for Reconvergence Analysis focuses on reconvergence hazard count, false alarm ratio, silicon-escape risk index. The goal is to convert issue observations into mechanism-backed closure decisions.

PROMPT
You see reconvergence hazard count, false alarm ratio, silicon-escape risk index in Reconvergence Analysis. Explain root cause and signoff decision.

STRONG ANSWER
1. Names crossing/reset class and context.
2. Explains Signals synchronized along different paths may reconverge with phase skew, creating functionally illegal combinations despite structurally legal crossings.
3. Requests reconvergence report, fanout cone map, functional hazard classification.
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

Reconvergence skew

signal A --sync path 1--                             logic merge -> hazard
signal B --sync path 2--/

Individually synchronized signals can still combine illegally.

Debug tree to narrate

ROOT-CAUSE TREE — Reconvergence Analysis

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

CDC/RDC deep dive

Reconvergence failures are timing + logic coupling hazards.

Concept diagram

RECONVERGENCE

branch A sync --                 -> merge logic -> illegal combination window
branch B sync --/

Metric graph

HAZARD REPRODUCTION RATE

before fix: 1/2000 runs
after fix: 0/100000 runs

Reports and artifacts

• reconvergence warnings

• gray transition checks

• hazard replay traces

• multi-bit strategy map

Mini case study

Gray pointer was legal, but downstream merge decoded mixed-era values during burst stress.

Debug branches

• Trace fanin cones

• align event windows

• verify decode assumptions

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

Signals synchronized along different paths may reconverge with phase skew, creating functionally illegal combinations despite structurally legal crossings.

Metric: reconvergence hazard count, false alarm ratio, silicon-escape risk index