frans@duvel.UUCP (Frans Meulenbroeks) (11/26/85)
[Follow-up to net.micro.pc]
Being in the process of writing a device driver for PC/AT under Xenix, I am
stuck with the following questions:
Can I just take an unused entry in the gdt table to use as a descriptor to a
piece of physical memory?
How can I determine whether an entry is free? Because it is all zero's?
Because it has no define in mmu.h?
Or is it better to use an ldt, and keeps things local for each task.
(This means creating a descriptor each time an interrupt is given, and
restoring it to its original state at the end of the interrupt routine)
Has anyone ever encountered these problems? If so, how did you solve them?
Have you ever encountered products which use memory mapped i/o? Do you
know how they "do the job"?
Thanks in advance!
--
Frans Meulenbroeks, Philips Microprocessor Development Systems
...!{seismo|philabs|decvax}!mcvax!philmds!frans