# PFES-ENG-031 — Firmware Compatibility Engineering

**Status:** Emerging  
**Knowledge Cycle Stages:** Understand, Validate, Apply

## Purpose

Determine when existing firmware can execute safely on different optical-drive hardware and when compatibility can avoid unnecessary modification.

## Engineering Problem

Shared CPU architecture does not guarantee compatibility. Memory maps, flash layout, servo/laser drivers, peripherals, board wiring, and optical mechanisms all matter.

## Historical Engineering Evolution

The known GDR-8163B to GDR-8050L cross-flash demonstrated native compatibility under sufficiently similar hardware. Investigation showed that many other MN103S drives are not directly compatible because their surrounding hardware differs.

## Engineering Discoveries

- Prefer native compatibility over capability transplantation when validated.
- Controller identity is necessary but insufficient.

## Architectural Decisions

- Validate cross-flash compatibility on hardware.
- Model electrical and peripheral dependencies.
- Do not infer compatibility from model or CPU alone.

## Knowledge Produced

- Compatibility matrices
- Cross-flash candidates
- Hardware dependency models

## Knowledge Consumed

- Firmware identity
- Board evidence
- Memory maps
- Controller and peripheral data

## Current Engineering State

Current confirmed example includes GDR-8163B hardware running GDR-8050L firmware. Broader compatibility remains a research area.

## Engineering Lessons

- A compatibility match can eliminate duplicate modification work.

## Negative Knowledge

Project Frankenstein no longer assumes:

- All MN103S firmware is interchangeable.
- Same model family guarantees board compatibility.

## Current Implementations

- Hardware fleet tests
- Firmware comparisons
- Board photography and controller identification

## Future Implementations

- Automated compatibility assessment
- Cross-flash validation framework

## Open Questions

To be expanded during engineering review.

## Why This Chapter Exists

Compatibility engineering identifies the simplest valid path before more invasive engineering begins.
