IDE, Panics, Traps

[Max Southall]

I've just finished working on a CompuAdd 20 MHz 286 machine with IDE
interface builtin that had terrible problems running SCO Xenix 286. It came
with an Award BIOS installed, and would generate PANIC and DOUBLE PANIC
in multiuser mode anywhere from a few seconds after boot to a couple of
hours at the longest, running 1 to 4 users.

After obtaining technical documentation for Chips & Technology's NEAT
chipset (the one utilized in the CompuAdd 220) I determined that the
problem was likely in the incomplete number of options shipped with
the systems's extended CMOS setup program by Award, XSET.

Not being able to obtain the details of Award's CMOS configuration, I
modified the JLS bilingual BIOS we had earlier developed for similar problems
on a 386 and wrote an extended CMOS setup program that allows configuration
and display of virtually all the CS8221B registers. After installing this
new version of the BIOS, and experimentation with register values, the
system now works flawlessly at 20 MHz.

The lesson? There are bus timing problems associated with using some
systems' implementations of IDE and Chips & Tech CS8221B chipsets that need 
to be addressed by using non-stock configuration of bus timing parameters.

But, they can be solved even if SCO doesn't get back to you (they didn't
in this case) and both the box manufacturer and Award BIOS supplier are unable
to help.

In any case, thanks to Alan Wendt (the box's frustrated owner) and Alex
Pournelle (iconoclast at large) for providing the impetus for this
solution.

- Max Southall - max at mamia.UUCP | mthvax!mamia!max
Hardware/Software Designer