# Fosi Audio MD3: mapping the DAC and replacing its controller firmware

> fosi-md3 investigates the Fosi Audio MD3 USB DAC and implements replacement firmware for its ESP32-S3 controller. Its notes map the USB mux, DAC I2C control, Savitech link and stock settings record from hardware observation and firmware disassembly; the ESP-IDF implementation preserves audio control and photo storage. The author reports testing on one unit.

- Type: Case study
- Targets: Firmware · Protocol
- Category: Independent reconstruction cases
- Relationship: Independent reconstruction project
- Sources reviewed: 2026-11-06
- Added to the catalog: 2026-11-08
- Original resource: <https://github.com/BenevolentFutures/fosi-md3>
- Primary source: <https://github.com/BenevolentFutures/fosi-md3/blob/c34b4bf757013764abf8e45c3c9d61c53a397042/README.md>
- Catalog page: <https://awesomerea.org/resources/fosi-md3-case/>
- Record JSON: <https://awesomerea.org/resources/fosi-md3-case/record.json>
- Chinese version: [简体中文](https://awesomerea.org/zh/resources/fosi-md3-case/index.md)

## Requirements & limits

- **Prerequisites:** A Fosi Audio MD3 unit and a backup of its own 32 MB flash for restoration.
- **Prerequisites:** ESP-IDF 5.5.1 and LVGL 9.2 for the replacement firmware; documented use was on macOS.
- **Limits:** The author reports testing on one unit; power transitions remain unverified.
- **License:** MIT license for the repository's original code and documentation.

## Primary sources

1. <https://github.com/BenevolentFutures/fosi-md3/blob/c34b4bf757013764abf8e45c3c9d61c53a397042/README.md>
2. <https://github.com/BenevolentFutures/fosi-md3/blob/c34b4bf757013764abf8e45c3c9d61c53a397042/docs/hardware.md>

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## About this entry

The description was reviewed against primary sources.
Original editorial content: MIT. Linked projects, papers and assets retain their own rights and licenses.