Reconvergence Analysis: Step-by-Step Walkthrough

Step-by-step analysis walkthrough

Use this sequence when owning Reconvergence Analysis in a signoff review.

1. Inspect warning class and severity.

2. Trace crossing endpoints and domains.

3. Check protocol/reset assumptions against spec.

4. Review synchronizer or FIFO implementation detail.

5. Run focused assertion or formal check.

6. Draft fix options with risk and schedule impact.

7. Execute regression and publish closure memo.

Artifacts to collect

• reconvergence report, fanout cone map, functional hazard classification

• crossing inventory

• waiver board notes

• regression report

Decision memo template

CDC/RDC DECISION MEMO — Reconvergence Analysis
risk class:
mechanism:
evidence:
fix/waiver:
owners: CDC owner, verification owner, design owner

Reference visuals

Reconvergence skew

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

Individually synchronized signals can still combine illegally.

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