Building and Flashing

To compile arm-none-eabi- tools from should be in the path. On Ubuntu, you can install the tools:

sudo apt-get install gcc-arm-none-eabi gdb-arm-none-eabi binutils-arm-none-eabi

Compilation options can be saved in Main targets:

make                 # Make with BLE support
make BLE=0           # Make without BLE support
make BLE=0 S110=0    # Make without BLE and without Softdevice in flash (see bellow)

make flash           # Flash firmware with jtag
make factory_reset   # Erase device and flash softdevice, bootloaders, and firmware


When running without softdevice (S110=0) the firmware is loaded at the beginning of the flash and is running alone in the CPU.

When running with Softdevive (S110=1) independent of if BLE is activated or not, the flash is filled as follow:

+--------------+ 256k
|     MBS      |    Write protected
+--------------+ 252k
|  Bootloader  |
+--------------+ 232k
|              |
|              |
|              |
|              |
|              |
|  Firmware    |
+--------------+ 88K
|              |
|              |
|              |
|              |
|              |
|              |
|  Softdevice  |
+--------------+ 4K
|     MBR      |    Write protected
+--------------+ 0
  • MBR Softdevice Master Boot Record.
  • SoftDevice S110 Bluetooth stack
  • Firmware This firmware
  • Bootloader Bluetooth/Shockburst bootloader
  • MBS Master Boot Switch

Boot sequence:

 MBR ----> MBS ----> Bootloader ----> Firmware

The MBR is part of the Softdevice. It boots the CPU and jump to MBS. The MBR contains methods to start the Softdevice and can flash softdevice and bootloader.

The MBS handles the ON/OFF button and communicate the duration of the press to the bootloader so that the bootloader knows what to boot. The reason for the MBS is to allow updating the bootloader over the air while still having a write-protected piece of software that can start the STM32 in USB DFU mode for recovery (the STM32 has access to the NRF51 SWD programming port). The boot switch is as follow:

Press time Blue LED state Program booted
Short Still Firmware
Long (>3s) Slow blink Bootloader
Very long (>5s) Fast blink Stays in MBS and power STM32 in USB DFU mode

The bootloader, if selected, starts the STM32 in bootloader mode and initialize both BLE and Shockburst (ESB) radio. It can flash everything but MBR and MBS. It also acts as a bridge to the STM32 bootloader.

If not selected, the bootloader jumps to the firmware.