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List:       linux-kernel
Subject:    Re: [preview] Latest AMD & VIA IDE drivers with UDMA100 support
From:       Andre Hedrick <andre () linux-ide ! org>
Date:       2001-01-21 20:49:40
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On Sun, 21 Jan 2001, Vojtech Pavlik wrote:

> On Sun, Jan 21, 2001 at 01:42:41PM +0100, Mike Galbraith wrote:
> > On Sun, 21 Jan 2001, Vojtech Pavlik wrote:
> > 
> > > On Sat, Jan 20, 2001 at 02:57:07PM -0800, Andre Hedrick wrote:
> > > 
> > > > chipset ---\
> > > >             |
> > > >             \---------IDC-header
> > > > 
> > > > chipset ---+
> > > >            |
> > > >            +----------IDC-header
> > > > 
> > > > These are nearly the same but the corners cause bounce and iCRC's
> > 
> > I don't see how anyone can influence risetime falltime or impedance
> > matching [1] issues via software timing changes.
> > 
> > (the top drawing is what you see on a poorly designed board.. long
> > rise/fall times often cause worse problems than [slight] ringing)
> > 
> > > Well, there are other ways the motherboard maker can screw up the
> > > traces, and often this happens:
> > > 
> > > chipset --------\
> > >                 |
> > > chipset ------\ |
> > >               | \------ header
> > >               \-------- header
> > > 
> > 
> > Can you compensate for these things (to any degree?) in software?
> 
> Not really. Slowing the data rate down is in my opinion the only way to
> compensate for this. Btw, the chipset only controls the write data rate
> with UDMA. The read rate is controlled by the drive.
> 
> > 1.  Only a software guy would call it 'bounce'.. sounds funny ;-)

Er...I help design some of the hardware and the rules, so I do more than
just software.  So does 'echo' or 'reflections'sound better than 'bounce'?

Cheers,

Andre Hedrick
Linux ATA Development

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