Xenix-386 + 80287 --> garbage
Richard Bassett
fredb at cheops.OZ
Tue Apr 12 17:32:23 AEST 1988
Hardware: 80386 16Mhz (NEC Powermate-386)
80287-8 8MHz 16-bit coprocessor
O/S: Xenix-386 v2.2.1 or v2.46 (vpix update)
Problem: occasionally (order once per 10 seconds) the FPU
gives garbage output.
When: arises when more than one process is using the
287, eg 1 process writes floating-point numbers in
ASCII to a pipe, another process reads them & converts
them to binary.
Does not seem to arise when only 1 process is doing heavy
floating-point work.
Random digits in the data are garbage, eg 'U'.
Some calculated results are wrong, eg zero or 999.99*.
When the job is repeated, corruption will occur in a
different place.
Same software runs fine (but 5 times slower - what are
all the claims about a 386 in software being as fast as a
287?) if the FPU is removed. It's also unlikely that bugs
in printf() could cause the corrupted digits.
Note: Xenix-386 claims to support a 386-287 combination.
The 8MHz 287 was purchased from NEC.
I tried a second 287 - same result.
Question: Has anybody else had this problem? What can I do about it?
* Is it a hardware timing problem? -> Does Xenix behave OK
on other 386-287 harware? -> Would a 10MHz 287 fix it?
* Is it a software problem? Is Xenix not saving sufficient
FPU status data when it task-switches?
Thanks in advance,
--
R J Bassett, Dept of Textile Tech, Uni of NSW,
PO Box 1, Kensington, NSW 2033, AUSTRALIA : Ph. +61 2 697 4454
--
ACSnet: fredb at cheops.oz
ARPA: fredb at cheops.oz.au
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