Access uart4 on Hummingboard-i2eX (Debian)?

I am using your Debian (wheezy) on a SolidRun Hummingboard-i2eX.

uname -a

Linux cubox-i 3.14.14-cubox-i #2 SMP Mon Aug 31 19:36:11 CDT 2015 armv7l GNU/Linux
 

In /dev, it looks like there are two IMX serial devices:

 ls -l /dev/ttymxc*
crw-rw---T 1 root dialout 207, 16 Feb  4  2001 /dev/ttymxc0
crw-rw---T 1 root dialout 207, 19 Feb  4  2001 /dev/ttymxc3
 

I can send/receive data from /dev/ttymxc0 (uart1) by using pin 8 (Tx) and pin 10 (Rx) of the 26-pin header on the board.

But how can I access /dev/ttymxc3 (uart4)?  Is there a pin somewhere on the board that I can connect to so I that I can send serial input to uart4?

Thank you.