m6-reveng

This repo contains information and tools for reverse engineering the $7 M6 smart fitness band.

Hardware

The SoC (system-on-a-chip) is a Telink TLSR8232.

• Datasheet
• 32-bit proprietary MCU
  • Closed ture, not a lot of resources about it
  • 24 MHz clock speed
• 16kB of SRAM
• 512kB of flash
• 32kHz oscillator for low power mode
• SWS (Single Wire Slave) interface for debugging and programming

The Setup

The Telink TLSR82xx series SoCs are debugged and programmed using the closed SWS (Single Wire Slave, or SWire) protocol. pvvx did a fantastic job reverse engineering this protocol and creating an alternative programmer based on the STM32 Blue Pill board. The TlsrTools project contains both the STM32 software (SWireSTM32) and a Windows GUI application for controlling the STM32 board.

The TlsrTools project was developed for the TLSR826x. I originally introduced changes to this project, but later I realized our TLSR8232 chip uses the same SWS protocol. This means we can simply flash this precompiled binary to our STM32 and use it as the middleman for debugging the M6.

I did not use the Windows GUI application, and instead wrote my own Python script (tlrs82-debugger-client.py) that connects to and controlls the STM32 via USB. The commands and timings are tailored for the TLSR8232 SoC, but should be easily adaptable for other TLSR82xx chips.

Reading the chip ID

Register 0x007e is a special register in the TLSR that contains the chip identification. This is a good way to verify that everything is working as expected.

$ python tlsr82-debugger-client.py --serial-port /dev/cu.usbmodem6D8E448E55511 get_soc_id
Found and set suitable SWS speed: 7
SOC ID: 0x5316

Dumping the RAM

$ python tlsr82-debugger-client.py --serial-port /dev/cu.usbmodem6D8E448E55511 dump_ram ram.bin
Found and set suitable SWS speed: 7
Dumping ram to ram.bin...
0x0000 00.00%
0x0100 00.39%
...
0xfe00 99.22%
0xff00 99.61%
Writing 65536 bytes to ram.bin

Dumping the flash

$ python tlsr82-debugger-client.py --serial-port /dev/cu.usbmodem6D8E448E55511 dump_flash flash.bin
Found and set suitable SWS speed: 7
Dumping flash to flash.bin...
CPU stop.
CSN high.
0x000000 00.00%
0x000100 00.05%
0x000200 00.10
...
0x07cd00 99.85%
0x07ce00 99.90%
0x07cf00 99.95%
Writing 512000 bytes to flash.bin