A CDC/DFU/UF2 bootloader for Nordic nRF52 microcontroller. UF2 is an easy-to-use bootloader that appears as a flash drive. You can just copy .uf2-format application images to the flash drive to load new firmware. See https://github.com/Microsoft/uf2 for more information.

DFU via serial/CDC requires adafruit-nrfutil, a modified version of Nordic nrfutil. Install python3 if it is not installed already and run this command to install adafruit-nrfutil from PyPi:

$ pip3 install --user adafruit-nrfutil

Officially supported boards are:

• Adafruit CLUE
• Adafruit Circuit Playground Bluefruit
• Adafruit Feather nRF52832
• Adafruit Feather nRF52840 Express
• Adafruit Feather nRF52840 Sense
• Adafruit ItsyBitsy nRF52840 Express
• Adafruit LED Glasses Driver nRF52840
• Adafruit Metro nRF52840 Express
• Raytac MDBT50Q-RX Dongle

In addition, there is also lots of other 3rd-party boards which are added by other makers, users and community. Check out the complete list of all boards here.

• DFU over Serial and OTA (application, Bootloader+SD)
• Self-upgradable via Serial and OTA
• DFU using UF2 (https://github.com/Microsoft/uf2) (application only)
• Auto-enter DFU briefly on startup for DTR auto-reset trick (832 only)
• Supports dual bank firmware updates (disabled by default)
• Supports signed firmware updates (disabled by default)

Note: For OTA, Packet Receipt Notification (PRN) must be 8 or less, which can be configured in nRF DFU. Otherwise, the bootloader will run out of memory.

There are two pins, DFU and FRST that bootloader will check upon reset/power:

• Double Reset Reset twice within 500 ms will enter DFU with UF2 and CDC support (only works with nRF52840)
• DFU = LOW and FRST = HIGH: Enter bootloader with UF2 and CDC support
• DFU = LOW and FRST = LOW: Enter bootloader with OTA, to upgrade with a mobile application such as Nordic nrfConnect/Toolbox
• DFU = HIGH and FRST = LOW: Factory Reset mode: erase firmware application and its data
• DFU = HIGH and FRST = HIGH: Go to application code if it is present, otherwise enter DFU with UF2
• The GPREGRET register can also be set to force the bootloader can enter any of above modes (plus a CDC-only mode for Arduino). GPREGRET is set by the application before performing a soft reset.

#include "nrf_nvic.h"
void reset_to_uf2(void) {
  NRF_POWER->GPREGRET = 0x57; // 0xA8 OTA, 0x4e Serial
  NVIC_SystemReset();         // or sd_nvic_SystemReset();
}

On the Nordic PCA10056 DK board, DFU is connected to Button1, and FRST is connected to Button2. So holding down Button1 while clicking RESET will put the board into USB bootloader mode, with UF2 and CDC support. Holding down Button2 while clicking RESET will put the board into OTA (over-the-air) bootloader mode.

On the Nordic PCA10059 Dongle board, DFU is connected to the white button. FRST is connected to pin 1.10. Ground it to pull FRST low, as if you had pushed an FRST button. There is an adjacent ground pad.

For other boards, please check the board definition for details.

To create your own UF2 DFU update image, simply use the Python conversion script on a .bin file or .hex file, specifying the family as 0xADA52840 (nRF52840) or 0x621E937A (nRF52833).

nRF52840
uf2conv.py firmware.hex -c -f 0xADA52840

nRF52833
uf2conv.py firmware.hex -c -f 0x621E937A

If using a .bin file with the conversion script you must specify application address with the -b switch, this address depend on the SoftDevice size/version e.g S140 v6 is 0x26000, v7 is 0x27000

nRF52840
uf2conv.py firmware.bin -c -b 0x26000 -f 0xADA52840

nRF52833
uf2conv.py firmware.bin -c -b 0x27000 -f 0x621E937A

To create a UF2 image for bootloader from a .hex file using separated family of 0xd663823c

uf2conv.py bootloader.hex -c -f 0xd663823c

You can burn and/or upgrade the bootloader with either a J-link or DFU (serial) to a specific pre-built binary version without the hassle of installing a toolchain and compiling the code. This is preferred if you are not developing/customizing the bootloader. Pre-builtin binaries are available on GitHub releases

Note: The bootloader can be downgraded. Since the binary release is a merged version of both bootloader and the Nordic SoftDevice, you can freely upgrade/downgrade to any version you like.

You should only continue if you are looking to develop bootloader for your own. You must have have a J-Link available to "unbrick" your device.

• ARM GCC
• Nordic's nRF5x Command Line Tools
• Python IntelHex

Firstly clone this repo including its submodules with following command:

git clone --recurse-submodules https://github.com/adafruit/Adafruit_nRF52_Bootloader

For git versions before 2.13.0 you have to do that manually:

git clone https://github.com/adafruit/Adafruit_nRF52_Bootloader
cd Adafruit_nRF52_Bootloader
git submodule update --init

Then build it with make BOARD={board} all, for example:

make BOARD=feather_nrf52840_express all

For the list of supported boards, run make without BOARD= :

make
You must provide a BOARD parameter with 'BOARD='
Supported boards are: feather_nrf52840_express feather_nrf52840_express pca10056
Makefile:90: *** BOARD not defined.  Stop

Firstly initialize your build environment by passing your board to cmake via -DBOARD={board}:

mkdir build
cd build
cmake .. -DBOARD=feather_nrf52840_express 

And then build it with:

make

You can also use the generator of your choice. For example adding the -GNinja and then you can invoke ninja build instead of make.

To list all supported targets, run:

cmake --build . --target help

To build individual targets, you can specify it directly with make or using cmake --build:

make bootloader
cmake --build . --target bootloader

To flash the bootloader (without softdevice/mbr) using JLink:

make BOARD=feather_nrf52840_express flash

If you are using pyocd as debugger, add FLASHER=pyocd to make command:

make BOARD=feather_nrf52840_express FLASHER=pyocd flash

To upgrade the bootloader using DFU Serial via port /dev/ttyACM0

make BOARD=feather_nrf52840_express SERIAL=/dev/ttyACM0 flash-dfu

To flash SoftDevice (will also erase chip):

make BOARD=feather_nrf52840_express flash-sd

To flash MBR only

make BOARD=feather_nrf52840_express flash-mbr

This bootloader can split the FLASH memory into 2 partitions, one for the last successfully uploaded firmware, and the other for the new firmware that is being uploaded. In case the firmware upload fails, the bootloader will revert to the last working firmware version. The only drawback is that the maximum firmware size is half of the device FLASH size: That is why it is disabled by default. You can enable this feature by passing DUALBANK_FW=1 to the make process while compiling the bootloader

This bootloader can validate that the uploaded firmware is digitally signed, and refuse to install unsigned or signed with the improper key firmware. Because this will make Arduino uploads stop working (because they are not digitally signed), this feature is disabled by default. But if you want to ensure noone else is allowed to upload firmware to your device, this option is probably what you want to enable.

To create a signing key, you will need the adafruit-nrfutil utility. First, generate a signing key and store at given path by using

adafruit-nrfutil keys --gen-key stored_key.pem

This command will create a signing key and store it in the file stored_key.pem. STORE THIS FILE IN A SAFE PLACE, as without it, you won't be able to sign your firmware packages, and the bootloader will refuse to flash them!!

Now, you must show the verification key (that is calculated from the signing key):

adafruit-nrfutil keys --show-vk code stored_key.pem

This command will read your signing key (from the file stored_key.pem) and display C source code with the Qx and Qy arrays: Something along the lines

static uint8_t Qx[] = { ... };
static uint8_t Qy[] = { ... };

You must save the Qx and Qy values, remove all spaces, and pass them to the make command line

make BOARD=feather_nrf52840_express SIGNED_FW=1 SIGNED_FW_QX='Qx values' SIGNED_FW_QY='Qy values'

And replace Qx values with the Qx array values, and the Qy values with the Qy array values. That will create a bootloader that ONLY accepts firmware signed with the stored_key.pem signing key. Take into account that the option SIGNED_FW=1 is what enables to build a bootloader that enforces signing, and will ALSO result in disabling UF2 support, as UF2 format does NOT support signing keys. There is an option (only for testing!) called FORCE_UF2 that will FORCE UF2 support on bootloaders that enforce firmware security. It is there to bypass security so you can test a secure bootloader and have a way to recover it something goes wrong, but should NEVER be used if you want to enforce security

Finally, to create a signed firmware application/bootloader update package, you can use, for example

adafruit-nrfutil dfu genpkg --dev-type 0x0052 --sd-req 0x0123 --application "application.hex" --key-file "stored_key.pem" "application_package.zip"

Please, use full paths for all files. The examples omit them for clarity!

And, to upload it to your device,

adafruit-nrfutil.exe --verbose dfu serial -pkg "application_package.zip" -p /dev/tty0 -b 115200

If you get the following error ...

make BOARD=feather_nrf52840_express all
Compiling file: main.c
/bin/sh: /usr/bin/arm-none-eabi-gcc: No such file or directory
make: *** [_build/main.o] Error 127

... you may need to pass the location of the GCC ARM toolchain binaries to make using the variable CROSS_COMPILE as below:

make CROSS_COMPILE=/opt/gcc-arm-none-eabi-9-2019-q4-major/bin/arm-none-eabi- BOARD=feather_nrf52832 all

For other compile errors, check the gcc version with arm-none-eabi-gcc --version to insure it is at least 9.x.

Install python-intelhex with

pip install intelhex

Make sure that nrfjprog is available from the command-line. This binary is part of Nordic's nRF5x Command Line Tools.