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From: marz@cbnewsm.att.com
Newsgroups: comp.sys.att,comp.unix.sysv386
Subject: Re: Dirty Rotten DMA problem (?)  Simultaneous tape & diskette use
Summary: DMA broken with two floppies ...
Keywords: DMA
Message-ID: <1990Nov12.181646.24873@cbnewsm.att.com>
Date: 12 Nov 90 18:16:46 GMT
References: <1990Oct31.190027.8613@informix.com> <1990Nov7.155748.12583@oct1.UUCP>
Followup-To: poster
Distribution: na
Organization: AT&T Bell Laboratories
Lines: 39

In article <1990Nov7.155748.12583@oct1.UUCP>, mason@oct1.UUCP (David Mason) writes:
> In article <1990Oct31.190027.8613@informix.com> aland@infmx.informix.com
> (Colonel Panic) writes:
> >Situation: while doing a mass cpio to the streaming tape, I try to
> >           format some 3.5" floppies or dd some disk-resident floppy
> >           images to them.  I keep getting i/o errors on the diskettes.
> >           If I try the same operations while the tape drive is not in
> >           use, no problems arise.
> >
> >Since both are using DMA, I suspect that the DMA buffering in the
> >kernel is going haywire.  Current pertinent kernel parms are DMAEXCL=0
> >(allow simultaneous DMA) and DMAABLEBUF=256.
> 
> As a matter of interest, the Interactive 2.2 (== 3.2.2) release notes
> state the following, under "Known Problems and Bugs":
> 
>         "On machines with certain types of DMA chips, concurrent
>         use of two DMA-based devices (such as diskette drive
>         and a tape controller) can result in erroneous data
>         transfers or aborted commands."
> 
> No saying which chips, of course.  Haven't seen the problem myself. 
> As far as I know, AT&T 3.2.2 is written by ISC, so it is likely that
> this problem will appear in AT&T 386 Unix.
> --------------------
> David        |      mason@oct1.UUCP (David Mason)
>              |      olsa99!oct1!mason@ddsw1.MCS.COM
>              |      <well connected>!ddsw1!olsa99!oct1!mason


I'll go you one better.  Try formatting a floppy from UNIX and using the
other floppy from vpix at the same time.  You get exactly the same
problem described above.

I wonder if turning off simultaneous DMA in the config file would help this
case.  Anybody try this yet?

						Martin Zam
						(201)564-2554