DMA (maybe) and tape drive problem (PANIC)

[Todd Koeckeritz]

I have run into a rather hard to solve problem and would appreciate
any input all you netters might have.  I have a 386 (Mylex MX Revision
1.01 25Mhz) motherboard, an Archive VP402 card controlling an Archive
150M VP tape drive and an Adaptec ACB-2322B controlling a 300M disk
all running under Xenix SysV 2.3.2.  The problem I am having is that I
can write tapes fine (never had a problem here), but sometimes when I
am reading the tapes I'll panic with a general protection fault or a
non-recoverable kernel page fault.  This will happen whether I am just
listing the files (as in tar tvf or cpio -iBtvc or even dd), dumping
everything to the bitbucket (/dev/null) or actually attempting to put
the files on disk.

I do have other devices in my system, however this is the most basic
hardware configuration in which I can dupicate the problem.  My IRQs
have all been scoped out many times (2/25, 3, 4, 5 and 7 for the tape)
and I have tried both DMA channels (1 and 3) and many of the
combinations of the above.  The I/O addr of the tape drive is 0x220
and doesn't appear to conflict with anything else.  I can cause this
to happen in single user or full up, I have beat my memory and disk to
a pulp attempting to test new configurations and isolate the problem.

To me it has boiled down to three possibilities:
1) A bug in the tape driver or Xenix, although I would expect to have
   seen some other flames about this.
2) A flakey tape controller card:  temperature appears to have some
   effect.  It happens more "reliably" if my system cabinet is on than
   when it is off.
3) A problem with the motherboard (DMA Controllers or design)

The only people I haven't talked to yet are Archive and the net.  SCO
of course wouldn't talk to me (mail or voice) to confirm or deny any
complicity, and Mylex disavowed that they had ever had a problem with
their motherboards (I have heard they did from several sources, can
anyone help to confirm or deny this ?).

Has anyone ran into a similar problem ?  Or is their a known problem
with any of the equipment I have mentioned ?  This is a last ditch
effort to solve the problem before I must go down and away while I
track Mylex and whoever else must get involved in solving the problem.

I would appreciate any guesses or new lines of thought in debugging
this situation.  E-Mail me if your answers are a little tentative.

Thanks in advance.

-- 
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|  Todd Koeckeritz        zaz at jersey                 (crash!orbit!jersey!zaz) |
|  Euler Solutions, Inc., Minneapolis, MN, USA H:(612)537-4264 W:(612)635-0088|
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