uhoh/docs/SERIAL.md

Serial Access to Comma Three

Charge the device fully without booting it (e.g. as when ded). I used Pine64 PinePower charger with USB-C.

Note, this device appears to be very sensitive to cable quality and length. So far the only cable that has worked has been the short thick USB-C cable that shipped with the unit.

# USB device connects with serial FTDI.
# 115200 8N1, no flow control

minicom -D /dev/ttyUSB0

Root user is comma. Not sure what password is, but I logged in so it was something easy if it is set. The comma has sudo access.