Thanks to the National Computer Science School,  I'm
now the proud owner of a BBC micro:bit. The micro:bit has the ability
to provide a python REPL over USB serial but when plugging it into my
Gentoo machine, the micro:bit doesn't show up in
Like most things, a kernel module is required to provide the drivers
for the USB serial interface. On first inspection you would think that
CONFIG_USB_SERIAL_CONSOLE is the correct module, but no.
The micro:bit's REPL is actually treated as a USB modem which requires
CONFIG_USB_ACM to be set.
Device Drivers ---> [*] USB Support ---> <*> USB Modem (CDC ACM) support
Now that the module is enabled, rebuild the kernel  and reboot. Once
rebooted plug in the micro:bit and there should be a new device in
/dev/ttyACM0 (or something
similar). Now it's as simple as connecting to your micro:bit REPL using
your serial console client of choice!
picocom /dev/ttyACM0 -b 115200
The micro:bit documentation as some more examples.