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Date: Thu, 29 Aug 2002 19:25:19 -0400 (EDT)
From: Mark Hahn <hahn@physics.mcmaster.ca>
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To: James Di Toro <jditoro3@coastalcreditllc.com>
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Subject: Re: Passing kernel parameters
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> Unfortunately this is not working.  dmesg for ide still shows the following:
>          ide: Assuming 33MHz system bus speed for PIO modes; override with 
> idebus=xx
> 
> despite the fact that I've specified 'idebus=66' and the following lines note:
> 
>          VP_IDE: VIA vt82c596b (rev 12) IDE UDMA66 controller on pci00:07.1

note that it says *system* bus speed.  that is, the clock fed to the IDE 
controller (usually the PCI clock, 33 MHz).  this is NOT the transfer mode!

by lying to the driver that "idebus=66", all you accomplish is making your 
transfers half the speed they should be.  the driver says 
	"since the clock period is 15ns, and I want (say) udma33
	(16b every 60ns), I'll tell the controler to do 16b every 4 clocks."

alas, the real period is 30ns, so you get 16b every 120ns.  voila, udma16 ;(

summary: don't lie to the driver; the default is probably correct.

regards, mark hahn.

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