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Date: Sun, 10 Jan 1999 23:09:39 +0100
From: Stefan Esser <se@mi.uni-koeln.de>
To: lcremean@tidalwave.net
Cc: Kenneth Wayne Culver <culverk@wam.umd.edu>, freebsd-current@FreeBSD.ORG,
        Stefan Esser <se@FreeBSD.ORG>
Subject: Re: ide_pci
Message-ID: <19990110230939.A43344@dialup124.mi.uni-koeln.de>
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	Kenneth Wayne Culver <culverk@wam.umd.edu>,
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References: <Pine.GSO.3.95q.990110000744.12864D-100000@rac4.wam.umd.edu> <19990110024647.A50225@tidalwave.net>
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In-Reply-To: <19990110024647.A50225@tidalwave.net>; from Lee Cremeans on Sun, Jan 10, 1999 at 02:46:47AM -0500
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On 1999-01-10 02:46 -0500, Lee Cremeans <lee@st-lcremean.tidalwave.net> wrote:
> beautifully, pulling down 13+ MB/s from my Seagate Medalist Pro 9140, but
> writes were kinda recalcitrant, and I think that may have been because I
> overclocked the PCI bus on my board -- I need to test it at 33 MHz. I can't

EIDE DMA writes are directly coupled to the external clock
and will come out way too high if you overclock your CPU.

Some EIDE tolerate 10% to 15% higher bus clocks, but some 
fail even at 5% more than specified!

But it is possible to reduce the EIDE clock by choosing
a higher divider value in some controller register, unless
you are using an external clock of more than 100MHz ...

Going to DMA Mode 1 transfers should make writes work at
half the UDMA data rate times your overclocking factor,
which should still be fast enough ;-)

Regards, STefan

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