How to upgrade the Adafruit nRF52 bootloader

The Adafruit nRF52 bootloader is a USB-enabled CDC/DFU/UF2 bootloader for nRF52 boards. An advantage compared to Nordic Semiconductor's default bootloader is that you can just drag and drop your application firmware from your operating system's file explorer, without having to install any programming tools. For nRF52840 boards, you hold the reset button while sliding the USB connector in the USB port of your computer, or you tap the reset button twice within 500 ms. The bootloader then starts in DFU (device firmware upgrade) mode and behaves like a removable flash drive.

This device shows three virtual files:

INFO_UF2.TXT

contains information about the bootloader build and the board on which it's running

INDEX.HTM

redirects to a page that contains an IDE or other information about the board

CURRENT.UF2

the contents of the entire flash storage of the device

Flashing the device with new firmware is as easy as copying a UF2 file to the drive. After the file is copied, the drive is unmounted and the new firmware is running on the board. 1

However, the bootloader itself can't be upgraded like this. Today I had some problems with the April USB Dongle 52840 2 that interrupted the UF2 file transfer before it was finished. The dmesg command showed a call trace and some errors. As a result, the device was useless: I couldn't put any new firmware on it.

I was puzzled, but then I looked at the bootloader's version in INFO_UF2.TXT, and this was quite old: a 0.2.x version from 2018. I hoped that upgrading the bootloader would solve the problem.

Upgrading the Adafruit nRF52 bootloader is quite easy:

  1. Download the latest release of the bootloader. For the April USB Dongle 52840 and other devices based on Nordic Semiconductor's nRF52840 Dongle 3, the firmware file is pca10059_bootloader-0.5.0.zip for the bootloader and SoftDevice wireless protocol stack. PCA10059 is the official name of Nordic Semiconductor's nRF52840 Dongle.

  2. Unpack the ZIP file. You need the file pca10059_bootloader-0.5.0_s140_6.1.1.zip (yes, another ZIP file) in it.

  3. Install adafruit-nrfutil: pip3 install --user adafruit-nrfutil.

  4. Connect the board to your computer's USB port and flash the new bootloader package:

$ adafruit-nrfutil dfu serial --package pca10059_bootloader-0.5.0_s140_6.1.1.zip --port /dev/ttyACM0
Upgrading target on /dev/ttyACM0 with DFU package /home/koan/pca10059_bootloader-0.5.0_s140_6.1.1.zip. Flow control is disabled, Dual bank, Touch disabled
########################################
########################################
########################################
########################################
########################################
########################################
########################################
########################################
########################################
############
Activating new firmware
Device programmed.

After this, the INFO_UF2.TXT file contains UF2 Bootloader 0.5.0 lib/nrfx (v2.0.0) lib/tinyusb (0.9.0-22-g7cdeed54) lib/uf2 (remotes/origin/configupdate-9-gadbb8c7).

Luckily the upgraded bootloader solved my problem: I was able to flash the board with new UF2 application firmware.

1

The UF2 format for firmware has become quite popular in recent years. For instance, the Raspberry Pi Pico also has a bootloader that accepts UF2 files.

2

If you're looking for an nRF52840 device with a longer range than similar devices with a PCB-based antenna, I can definitely recommend the April USB Dongle 52840: in my experiments with the dongle as a Bluetooth Low Energy and a 802.15.4/Zigbee sniffer, the external antenna makes a big difference.

3

Another interesting nRF52840 board is the nRF52840 MDK USB Dongle from makerdiary. This is essentially a Nordic Semiconductor nRF52840 Dongle with the Adafruit nRF52 bootloader, sold in a case.