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From: aland@informix.com (Colonel Panic)
Newsgroups: comp.sys.att,comp.unix.sysv386
Subject: Re: Dirty Rotten DMA problem (?)  Simultaneous tape & diskette use
Keywords: DMA
Message-ID: <1990Nov17.005232.22133@informix.com>
Date: 17 Nov 90 00:52:32 GMT
References: <1990Oct31.190027.8613@informix.com> <1990Nov7.155748.12583@oct1.UUCP> <1990Nov11.205350.108@eslvcr.wimsey.bc.ca>
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In article <1990Nov11.205350.108@eslvcr.wimsey.bc.ca> ted@eslvcr.wimsey.bc.ca (Ted Powell) writes:
>In article <1990Nov7.155748.12583@oct1.UUCP> mason@oct1.UUCP (David Mason) writes:
>>>[...bad things happening when using both tape and floppy...]
>
>The AT&T 386 Unix does have the DMAEXCL parameter. Before I turned it
>off, I tried installing Fastback Plus on the DOS partition of the disk.
>The installation procedure includes a check for this DMA problem. My
>chip passed the test, so then I turned off DMAEXCL, which is ON by
>default.

The funny thing is... the AT&T doc states that "some machines' DMA 
controllers may not be able to handle simultaneous DMA...", but 
AT&T Support has never been able to give me a definitive answer as
to whether or not *their own machines* can handle it... (they use
discrete logic rather than a major name DMA controller chip, so it's 
not likely to be something I can find out from anyone else...)

>Seems to me the best thing for the Colonel to do (he didn't mention
>having tried it already) is to turn DMAEXCL back on and see whether this
>makes the problem go away. If it does, then it's chip replacement time.

The problem doesn't "go away", per se... I get Double Kernel Panics
if I *don't* set DMAEXCL to 0.  That's how I discovered the parm in
the first place.

>ted@eslvcr.wimsey.bc.ca   ...!ubc-cs!van-bc!eslvcr!ted    (Ted Powell)

--
Alan Denney      aland@informix.com      {pyramid|uunet}!infmx!aland

"I went to Wall Street with the desire to help change society for the
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