Drivers for uC/OS-II

Hello,

I am working on the DE2 board (cyclone2) with NIOS2 and uC/OS-II.

I need to write some OS drivers for some devices, for example USB or Ethernet.

I read a little about drivers in some ALTERA official docs and I didn't really understand how the drivers relate to the OS and how they interact with the Nios HAL.

Can someone please recommend the most simple devices to write drivers to, and direct me to where I can read about writing drivers for uC?

Thanks a lot,

Omri