Please make sure you've looked at, and built, the relevant labs on the TI wiki:
http://processors.wiki.ti.com/index.php/PRU_Training:_Hands-on_Labs
There are also several sample kernel drivers in the kernel source, artfully buried under Kernel Hacking:Kernel Hacking ->
[*] Sample Kernel Code ->
<M> Build rpmsg client -- (loadable modules only)
You'll need one of the recent BBB kernels, either TI 4.1 or Robert Nelson's BB kernel 4.1 or higher.
https://eewiki.net/display/linuxonarm/BeagleBone+Black
You'll also need to download the TI cgt-tools and SDK to build everything on your desktop, or if you're feeling adventurous you could
also try it on BeagleboneBlack using the apt package repos. If you have a quizzical expression right now, just follow the TI wiki pages.