Serial Port Enable?

[AidFTech]

I am planning on integrating Crankshaft into a Teensy-based infotainment system (so I can have Android Auto for navigation while listening to the radio or a CD); that will require UART communication with the Raspberry Pi. I can't find any information on how to enable/use the GPIO UART connection in Crankshaft, i.e. to map a serial command to a keystroke or even open the port. The standard Raspberry Pi commands don't seem to work... (albeit I am still relatively new to Pi) Has anyone tried this?