Please see the web site for more info:
To power the WARBL on, plug into USB or click button 3 (lowest button).
To manually power off the WARBL while under battery power, you can click the reset button (or use a button action assigned in the Configuration Tool, which by default is a long-press of button 3).
For updating the firmware, typical users would just hold down button 1 while plugging the WARBL in to USB and then drag/drop the supplied .uf2 file to the drive named WARBLBOOT. If the WARBL is already plugged in, you can also double-click the reset button to enter the bootloader mode. The most recent flash.uf2 file is located in the build/adafruit.nrf52.warbl2 directory.
Advanced users can use the Arduino IDE to modify and upload the code. Modify the code at your own risk and note that while modifying the battery management code won't have dangerous results it could result in reducing the lifespan of the battery.
Install / run the latest version of the Arduino IDE. You can download the latest version of the Arduino IDE here.
In Linux, the Arduino IDE requires that you be part of the dialout group to successfully detect and write to hardware (see here). If running id in a terminal does not list dialout as one of the groups your user belongs to, run sudo usermod -a -G dialout $USER, then log out and back in. Running id should now include the dialout group.
I used the Adafruit ItsyBitsy NRF52840 Express for prototyping WARBL, so the easiest way to set up the IDE is to install the Adafruit boards package, following the instructions here.
After installing this boards package, it is currently necessary to downgrade the package to v. 1.6.0 (in the Boards Manager in the IDE) because of an unresolved issue.
Download the WARBL2 code from this repository, and move the boards.local.txt file from the "firmware" directory into the directory on your machine that contains the boards.txt file for the Adafruit NR52 boards, typically found here:
Windows: C:\Users\(username)\AppData\Local\Arduino15\packages\adafruit\hardware\nrf52\1.6.0
Linux: /home/(username)/.arduino15/packages/adafruit/hardware/nrf52/1.6.0
Mac: ~/LibraryArduino15/packages/adafruit/hardware/nrf52/1.5.0/
Now open the warbl2_firmware.ino sketch that you saved in your sketchbook folder.
In the Tools menu select: Board: > Adafruit nRF52 > WARBL2
Next, you’ll need to install libraries included in the sketch that aren’t installed by default. To install them, go to Sketch > Include Library > Manage Libraries, then search for the name of each, one at a time. Then it will give you an option to install each one.
Then turn on “show verbose ouput" for both "compile" and "upload" under File > Preferences. Now, click the upload button and check that it compiles without errors.
Then, when it tries to upload, you should see this message at the bottom of the screen:
Waiting for upload port...
The serial CDC class on WARBL needs to be turned off to make it a USB MIDI class-compliant device. This also means that you won't be able to use the serial monitor in Arduino IDE, and you'll have to double-click the programming button to install firmware (as described above). To turn serial back on, you can comment out the following line in the sketch:
#define RELEASE //Uncomment for release version (turns off CDC)
Turning on CDC makes it easier to debug and makes it so uploads should proceed automatically.
Have fun!