Xiaomi Mi Band 4

Board	mi_band_4
Vendor	xiaomi
SoC	da14697

Overview

The Xiaomi Mi Band 4 is a fitness tracker built around the Renesas SmartBond DA14697 SoC, an ARM Cortex-M33 with an integrated Bluetooth LE 5.0 radio. This board definition is the result of reverse engineering the device so it can run open-source Zephyr RTOS based firmware.

Hardware

• Renesas SmartBond DA14697 SoC

  • ARM Cortex-M33 core

  • 512 KiB SRAM

  • Bluetooth LE 5.0

  • 1.4 V - 3.6 V supply

• 16 MiB external QSPI flash, mapped at 0x16000000

• 32 MHz and 32.768 kHz external crystals

• Raydium RM69310 AMOLED display driver (120 x 240, RGB565)

• Zinitix touch controller (I2C)

• Bosch BMI260 6-axis IMU (I2C)

• Texas Instruments AFE4900 heart rate analog front end (SPI/I2C)

• Azoteq IQS620 proximity / wear detection sensor (I2C)

System overview

Datasheets for the main components are available in the doc/datasheets directory of this repository.

Supported Features

The following features are supported (from the board’s twister YAML file):

Feature	Target
counter	mi_band_4
gpio	mi_band_4
hwinfo	mi_band_4
watchdog	mi_band_4
i2c	mi_band_4
rtc	mi_band_4
crypto	mi_band_4
dma	mi_band_4
memc	mi_band_4

The following components are not supported yet:

• Touch controller

• IMU

• Heart rate sensor

• Proximity sensor

• Power management and battery charging

Connections and IOs

Debug Pads

The SWD interface and power are exposed on test pads on the back of the PCB.

SWD and power test pads

Pad	Connect to
GND	Debug probe GND
+5V	5 V supply
SWCLK	Debug probe SWCLK
SWDIO	Debug probe SWDIO

Programming and Debugging

The following west runners are supported:

Runner	Default
ezflashcli	yes
jlink

Set up the Workspace

This repository is a west manifest repository and a Zephyr module, so the mi_band_4 board is available to west build once the workspace is initialized:

west init -m https://github.com/walidbadar/ZSband --mr main zsband-workspace
cd zsband-workspace
west update
west zephyr-export
west packages pip --install

Building

Here is an example for the Hello World application:

west build -b mi_band_4 zephyr/samples/hello_world

The board defconfig disables XIP (CONFIG_XIP=n) so that images can be loaded directly into SRAM for debugging. To build an image that executes from flash, enable XIP:

west build -b mi_band_4 zephyr/samples/hello_world -- -DCONFIG_XIP=y

Flashing

The board supports the ezflashcli (default) and jlink runners. After building an XIP image, flash it with:

west flash

To use J-Link instead:

west flash -r jlink

Loading into RAM

A non-XIP image can be loaded into SRAM and started without touching the flash using the J-Link helper script. It reads the initial stack pointer and reset vector from the image, loads zephyr.bin at 0x20000000 and jumps to it:

ZEPHYR_BASE=$PWD ZSband/scripts/jlink/ram-load.sh [MCU] [SRAM_BASE_ADDR]

MCU defaults to DA14697 and SRAM_BASE_ADDR to 0x20000000. The script expects the build directory at $ZEPHYR_BASE/build.

Debugging

Debug the application with J-Link:

west debug -r jlink

The console is routed to SEGGER RTT by default (CONFIG_RTT_CONSOLE=y). Open it with JLinkRTTViewer or JLinkRTTClient while the target is connected. The UART is also available on P0.8/P0.9 at 115200 baud.

Connecting to the Target

The SWD pads can be hard to keep in contact with. The auto-connect scripts retry until the target is detected, which helps with positioning the probe pins:

# J-Link, beeps when the target is found
cd ZSband/scripts/jlink && ./auto-connect.py

# Raspberry Pi SWD adapter (SWDIO = GPIO 23, SWCLK = GPIO 24)
cd ZSband/scripts/openocd && ./auto-connect.sh

Reading the Stock Firmware

The whole 16 MiB flash can be dumped with OpenOCD through a Raspberry Pi SWD adapter. The image is written to output.bin:

cd ZSband/scripts/openocd && ./flash-reader.sh

References

• DA1469x datasheet

• ZSBand repository