The uC/OS-II Realtime OS, by Jean Labrosse, is great for learning RTOS basics.
It comes with a 500 page
book which describes it in detail.
This is not to say that the OS is a toy. It's a full grown and very competent OS. It even has a DO178B
certification for use in medical and aviation products.
For more info about uC/OS-II, see Jean Labrosse's own pages at www.ucos-ii.com.
To get to the point..... I've made a port for the AVR processors, for version 2.95.2 of the AVR-GCC compiler.
Note that it is ONLY for version 2.92.2 !!!
You need to modify the likner file for later compiler versions.
Please do NOT ask me about this.
Comments are always welcome at jesperh@telia.com