Download Bootloader Package
To update the bootloader, you need a .zip file containing the latest version of the bootloader. Use the link below to download it. Then unzip the .zip you downloaded.
Download adafruit-nrfutil
You will also need the utility program "adafruit-nrfutil", which has slightly different names on different platforms.
On Linux, you can download and install adafruit-nrfutil by doing:
$ pip3 install --user adafruit-nrfutil
On MacOS, if you have python3 and pip3 installed, you can install via pip3, as above for Linux. Otherwise download adafruit-nrfutil-macos from this link:
Then make it executable by doing:
chmod +x adafruit-nrfutil-macos
On Windows, download adafruit-nrfutil.exe from this link:
Update Bootloader
To update the bootloader, first connect the board, and then double-click to get NRF52BOOT. In the commands below, substitute the name of the .zip file you downloaded for file given there.
On Linux, run this command:
adafruit-nrfutil --verbose dfu serial --package feather_nrf52840_express_bootloader-0.2.9_s140_6.1.1.zip -p /dev/ttyACM0 -b 115200 --singlebank --touch 1200
On MacOS, find out the device name for the connected board, by doing:
ls /dev/cu.*
The device name will be something like /dev/cu.usbmodem411. Use this command, substituting the device name you've discovered. If you are running it other than where you downloaded adafruit-nrfutil-macos, change the path to the command accordingly. If you installed it via pip3, it's just called adafruit-nrfutil, and it should be in your PATH.
./adafruit-nrfutil-macos --verbose dfu serial --package feather_nrf52840_express_bootloader-0.2.9_s140_6.1.1.zip -p /dev/cu.usbmodem411 -b 115200 --singlebank --touch 1200
On Windows, use this command, in the folder where you downloaded the other two files above. You'll need to specify the correct COM port, instead of COMxx. Look in Device Manager for the name of the COM port (it will be listed as a "USB Serial Device" on Windows 10) after you have double-clicked the reset button.
adafruit-nrfutil.exe --verbose dfu serial --package feather_nrf52840_express_bootloader-0.2.9_s140_6.1.1.zip --port COMxx -b 115200 --singlebank --touch 1200
Once done, click the reset button again - the bootloader will be running!
