Setting up tty ports on Beaglebone Black with Angstrom linux

I'm using a Beaglebone Black running the Angstrom v2012.12 build that came pre-loaded. I want to be able to connect another device to a serial port via the UART connections on the GPIO headers. The problem is I can't tell which /dev/tty devices these map to. When I try to access the /dev/ttyS? devices (e.g. using od /dev/ttyS2) I get a "read error: Input/output error". Can anyone tell me if the UARTS are mapped to tty devices by default, if so, which ones and if not how I can create the right devices?