Xenix Device Drivers

[Steve Harpster]

I'm running Xenix 286 and having problems writing a device driver (we
have no source either).  Basically, I'm trying to write to the enhanced color
graphics adapter (EGA) directly.  I know this starts at physical address
0xb8000 but I can't seem to get there.

The special files /dev/mem and /dev/kmem look like this:

		-------------		<- 0
		|    mem
		|
		|------------		<- kmemstart
		|    kmem
		|
		|------------
		|   more
		|   mem
		-------------
		-------------		<- ~0xa0000
		| I/O devs
		|
		-------------

So obviously I can't use /dev/[k]mem.

I haven't a clue as to what /dev/color or /dev/monochrome really do.
The documentation doesn't say much and kinds of hints that these are
worthless for what I'm trying to do.

Next step was to write a driver where the xxwrite() routine just used
cpass() to get a character from the user and stuff it into memory
starting at 0xb8000.

Sounds simple, right?  When trying to write though, the kernel panics
with a "General Protection Fault".  What does this REALLY mean?  I
thought that once inside xxwrite(), I would be in kernel mode.  Am I
still in user mode?  Do I have to write a "bottom half" to get to
kernel mode (yeechy way because there are no interrupts, per se)?
Or is there something else going on that I haven't thought of?
Do I really want to use /dev/color instead?

Any help would be GREATLY appreciated.

Stephen Harpster
Tellabs, Inc.
...ihnp4!tellab1!steve
-- 


...ihnp4!tellab1!steve
Steve Harpster
Tellabs, Inc.