# CH899: reconstructing the clock's MM32–ESP exchange

> CH899 firmware research reconstructs the UART exchange between the clock's MM32 movement controller and ESP8285 Wi-Fi module. It records wake, time and reset messages from stock behavior and implements replacement ESP firmware that adds Wi-Fi setup and timekeeping options while retaining the original movement controller.

- 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/maddenste/Chouchin-CH899-Firmware>
- Primary source: <https://github.com/maddenste/Chouchin-CH899-Firmware/blob/aaf649283633ce3a081879c90a691af2897b1e1b/docs/PROTOCOL.md>
- Catalog page: <https://awesomerea.org/resources/chouchin-ch899-firmware-case/>
- Record JSON: <https://awesomerea.org/resources/chouchin-ch899-firmware-case/record.json>
- Chinese version: [简体中文](https://awesomerea.org/zh/resources/chouchin-ch899-firmware-case/index.md)

## Requirements & limits

- **Prerequisites:** The older CH899 clock board whose main chip is marked MM32.
- **Scope:** Replacement applies to the ESP8285 Wi-Fi firmware; the MM32 movement firmware remains in place.
- **License:** GPL-3.0-or-later license.

## Primary sources

1. <https://github.com/maddenste/Chouchin-CH899-Firmware/blob/aaf649283633ce3a081879c90a691af2897b1e1b/docs/PROTOCOL.md>
2. <https://github.com/maddenste/Chouchin-CH899-Firmware/blob/aaf649283633ce3a081879c90a691af2897b1e1b/README.md>
3. <https://github.com/maddenste/Chouchin-CH899-Firmware/blob/aaf649283633ce3a081879c90a691af2897b1e1b/docs/REVERSE_ENGINEERING.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.