ZSBand: Reverse Engineering of Xiaomi Mi Band 4 for Zephyr Smart Band Firmware

Overview

This document outlines a systematic approach to hack, reverse engineer, and eventually develop custom Zephyr RTOS based firmware for the Xiaomi Mi Band 4. This project aims to understand the device's hardware components, communication protocols, and system architecture to create an open-source alternative firmware.

System Architecture

Project Phases

Phase 1: Hardware Analysis

• Map debug ports (SWD, UART) and test points
• Document PCB layout and component connections
• Extract firmware through debug interfaces if accessible

Phase 2: Hardware Interfacing

• Establish connections to debug and communication interfaces
• Explore sensor protocols and register maps (GPIO, I2C, SPI)
• Create test code to verify peripheral access

Phase 3: Zephyr Port Development

• Create device tree source for Mi Band 4
• Implement drivers for display, sensors, and power management

Tools Required

Hardware Tools

• Logic Analyzer
• SWD debug probe (J-Link)
• Raspberry Pi

Software Tools

• Firmware analysis tools (Ghidra)
• Zephyr SDK (Getting Started)
• ezFlashCLI
• openOCD

Legal and Ethical Considerations

• Developing for personal use and research purposes only
• Avoiding distribution of copyrighted firmware components
• Focusing on interoperability and open standards
• Documenting for educational purposes