A login shell can be accessed through UART-A on the Colibri Evaluation board with a null modem cable. The communication settings are: 115200 8N1.
If you are using our Controller Board (cb20) you need a special USB/TTL-Serial-UART converter cable. The connector on the board is a 6-pin SIL connector, e.g. http://ch.farnell.com/ftdi/ttl-232r-3v3/kabel-usb-ttl-pegel-seriell-umsetzung/dp/1329311

UART-A (used for console, see above) and UART-B can be accessed on the cb20 board. Both can be written to with

echo "hello world" | sudo tee /dev/ttymxc0    # for console
echo "hello world" | sudo tee /dev/ttymxc1    # for UART-B