Xinu is a layered, multi-threaded operating system with preemptive scheduling, semaphores, message passing, and real time clock operations. A detailed description can be found in the text:

        Comer, Douglas E., Operating System Design: The Xinu Approach, Prentice-Hall, 1984.

This port contains version 7 of the software (including Internet protocol software and a user interface shell), and is described in:

        Comer, Douglas E., Operating System Design Vol 2: Internetworking with Xinu, Prentice-Hall, 1987.

See https://sites.google.com/site/avrxinu/project-definition