"Writing UNIX Device Drivers" by George Pajari (Addison Wesley) has some general how-to information and brief coverage of x86 topics.

SCO driver book.

SCO makes available the Advanced Hardware Developer's Kit This is the definitive guide for SCO-specific topics such as Kernel debuggers, Network drivers, Video drivers, and BTLDs that are not covered in any other place. If you're doing device drivers on or for SCO systems, you need this.

To order, visit: http://www3.sco.com/Products/layered/develop/ahdk.htm . You can also use the online version that SCO provides at: http://www2.sco.com:1996/dochome.html .
robertlipe@usa.net