FreeBSD Kernel Sources http://www.freebsd.org
NetBSD Kernel Sources http://www.netbsd.org
Writing Device Drivers: Tutorial and Reference; Tim Burke, Mark A. Parenti, Al, Wojtas; Digital Press, ISBN 1-55558-141-2.
Writing A Unix Device Driver; Janet I. Egan, Thomas J. Teixeira; John Wiley & Sons, ISBN 0-471-62859-X.
Writing Device Drivers for SCO Unix; Peter Kettle;