Reconvergence & Gray Coding

Section goal

Reconvergent fanout analysis, gray-code transfers, and robust multi-bit crossing strategies.

How to study this section

1. Start with topic hubs to classify problem shapes.

2. Use mechanism and reports pages to connect risk signals to evidence.

3. Practice debug and worked examples before signoff reviews.

4. Close with checklist and silicon impact before approving fixes or waivers.

Topics

1. gray-code-crossing/ — Gray Code Crossing

2. reconvergence-analysis/ — Reconvergence Analysis

3. multi-bit-strategies/ — Multi-bit Crossing Strategies

4. reconvergence-debug/ — Reconvergence Debug

Related topics

• CDC/RDC course hub

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?