Hi,
I published a 2 parts article on using the Beagle Bone Black realtime
units (PRUs). The first is an introduction:
http://www.embeddedrelated.com/showarticle/586.php
Following the first part, I received feedbacks from people regarding
using the C language to program the PRU. The second article discusses
this:
http://www.embeddedrelated.com/showarticle/603.php
I hope it helps,