Unless I'm mistaken, I'm pretty sure there's already a UART driver for the TX1 here: https://github.com/seL4/util_libs/blob/master/libplatsupport/src/mach/nvidia/serial.c

Feel free to ask further questions if this doesn't meet your needs though -- it should work for all 4 of the UARTs on the TX1.

Kofi Doku Atuah
Kernel engineer
DATA61 | CSIRO