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Path: sserve!newshost.anu.edu.au!munnari.oz.au!news.Hawaii.Edu!ames!agate!tfs.com!julian
From: julian@TFS.COM (Julian Elischer)
Subject: Re: [FreeBSD 1.0R] DMA Problems?
Message-ID: <CIAv9o.I6K@tfs.com>
Sender: usenet@tfs.com
Organization: TRW Financial Systems, Oakland, CA
References: <2eopau$hde@vixen.cso.uiuc.edu> <jmonroyCI6HqF.Hxu@netcom.com> <2eta3j$6t9@vixen.cso.uiuc.edu> <CI9EC4.AoB@genesis.nred.ma.us>
Date: Sun, 19 Dec 1993 20:51:24 GMT
Lines: 35
In article <CI9EC4.AoB@genesis.nred.ma.us>,
Steve Gerakines <steve2@genesis.nred.ma.us> wrote:
>I have neither an Adaptec nor a 3c507 and I'm the one who asked about
>this originally. Jesus was right (in this case anyhow :-)) when he said
>it had to do with the NEC 765A not being buffered and not receiving an
>ACK in time. (Sounds like this is basically what you're saying as well.)
>A couple of other people have confirmed that overruns during FDC DMA writes
>is a known and documented problem.
>Is there any known way to get around this other than just doing retries
>(over and over) or modifying your hardware?
Though you say that you have no adaptec, I will point out as a data point,
that on many machines the adaptec's default DMA settings interfere with
the correct operation of the floppy controller DMA. S nuch so, in fact that
the newest versions of the adaptec driver change the DMA behaviour settings to
reduce the problem.
It is fairly easy then to believe that other devices may have a similar effect,
however my guess is that mainly MASTERING DMA devices will do this as
SLAVE DMA devices go through a slightly different set-up of the
DMA controller. The change to fix the adaptec controls how MANY cycles
it will take in a row, before releasing the bus to other devices, rather than
the size of each cycle.
julian
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