386 chip "hangs" when in protected mode and 387 in place SCO Xenix

[Rob Freyder]

Greetings Folks,

I have about 14 HP Vectra 386/20 systems all with 387 co-processors. We run
SCO Xenix currently and have had a recurring problem that up until lately
has baffled us....  Whenever we would run SCO Professional (spreadsheet)
accessing the tape drive or floppy disks with tar or dd (the only ones i tested)
the system would "hang" without a single message.  I consulted the SCO database
and found that I was not alone in this dilemma.  There have been many others
that have had the same problem... 

I am not quoting but it goes something like this.  If you are in protected mode
and you are executing a 32 bit fp instr and access a DMA device the CPU will
"freeze" or "hang up".  This is only happens with certain releases of the
chip and is apparently not a problem with newest release.  SCO has a 
workaround that works on some machines (of course not on ours) ... IF it 
doesnt work on yours then you can disable the 387 until you are able to
replace the CPU...   8-(

Intel has documented this and I believe its referred to as "Erratum 21"

I need pointers on identifying these "defective" 386 chips and was wondering
if anyone has leads on diagnostic software that would verify my suspicions
regarding this "hanging" of the system... Also .. If I make a visual 
inspection of the chips what markings would tell me that it was the
type that "hangs" in protected mode.

And finally, ...What should we replace these with ?  Cost ?  Has anybody
else out there been through this ??  Help !

BTW , this problem doesnt manifest itself under DOS because, of course, DOS
doesnt run in protected mode.

Thanks in advance for any pointers, replies or suggestions that you might
have.

Rob
-- 
Rob Freyder                                  Core Laboratories a division of
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