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Date: Thu, 02 Jan 2003 23:00:56 +0100
From: Lionel Bouton <Lionel.Bouton@inet6.fr>
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To: Alan Cox <alan@lxorguk.ukuu.org.uk>, Andre Hedrick <andre@linux-ide.org>
Cc: Teodor Iacob <Teodor.Iacob@astral.kappa.ro>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: UDMA 133 on a 40 pin cable
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Happy new year everybody


Alan Cox wrote:

>It got CRC errors, not suprisingly and will drop back. Nevertheless it
>shouldnt have gotten this wrong, so more info would be good.
>  
>

I'm wondering some things about IDE 40/80 pin cables since some time ago :
- somehow the circuitry can make the difference between 40 and 80 pin 
(probably some pins are shorted or not by the cables or some 
cable-type-dependent impedance between wires is mesured) and set a bit 
for us to use.
- most probably the same circuitry can't verify the length of the cables 
or their overall quality but I'm unsure.

#1 How is the 40/80 pin detection done at the hardware level ?
#2 Are there any other cable-quality hardware tests done by the chipsets 
? How ?

I've encountered a barebone design (Mocha P4, uses 2.5" drives) where 
the IDE cable was 40-pin but :
- has a single drive connector instead of the common two,
- its length is only around 10 or 15 cm.
A buyer contacted me for SiS IDE driver directions on this platform and 
confirmed this at least for his purchase.

#3 Is the above cable electrically able to sustain 66+ UDMA transfers 
(could I hack a driver in order to bypass the 80pin cable detection and 
make it work properly) ?
#4 Are the electrical specs for 66+ UDMA transfers public (couldn't find 
by googling) ? Where can we find them ?
Here I mean some really basic specs (max Resistance/Capacity/Inductance 
between wires, max signal propagation delays and so on) and not general 
high level specs (material, connector design, length ranges allowed in 
the general 80-pin, 2 drives case).

Any hints on these Andre ?

LB.

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