Comer has a new edition of "Operating System Design: The Xinu Approach" that focuses on a Linksys/Cisco router. I've not read the text officially yet, but the drafts were very interesting. Purdue CS grad students use Xinu for the OS course projects (http://www.cs.purdue.edu/homes/cs503/).
P.S. I still maintain a very HLL is ideal for presenting multi-processing/multi-tasking to students.