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Date:      Thu, 23 Jan 1997 12:03:20 -0500
From:      John Duncan <jddst19+@pitt.edu>
To:        Nadav Eiron <nadav@barcode.co.il>
Cc:        Jen and Luke <isis@servtech.com>, "questions@FreeBSD.ORG" <questions@FreeBSD.ORG>
Subject:   RE: EIDE drives
Message-ID:  <01BC0927.31C06C40@ehdup-i-2.rmt.net.pitt.edu>

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----------
From: 	Doug White[SMTP:dwhite@gdi.uoregon.edu]
Sent: 	Wednesday, January 22, 1997 10:56 AM
To: 	Nadav Eiron
Cc: 	Jen and Luke; questions@FreeBSD.ORG
Subject: 	Re: EIDE drives


Here I go trying to understand the difference between EIDE and IDE and
screw it up massively.  :-)  Will someone please fill me in?  I don't
consider a difference between the two.

----

What I gather on the subject: First and foremost, the ide/eide/ata/ata-2
specifications only truly became specified with ata, and nobody felt the
need to follow the specification exactly. Before the ata-2 standard came
out, there were vlb card manufacturers and drive makers who wanted to
provide a 32-bit bus and a couple of higher clock rates to the drives, so
they could write "32-bit" on their boxes, and people would buy them.

FreeBSD supports some of these features, such as 32-bit pio multi-block
transfers, and the ability to select in the kernel-config whether we want to
use these features, and how much we want to transfer. What we don't seem
to provide is the selectable clock-rates for the drives. My promise bios starts
drives automatically at speed 2, and then the win95 driver steps this speed
up to the reccommended setting (or user-defined setting) for the drive.

The driver claims, although my drives are old enough to not support it, that
the speed can be selected from 0 to 8 (I don't know the relations off-hand)
and that the speed can also be selected per the ATA spec. (This, sadly,
I also cannot test.)

There is actually only a small set of "EIDE" enhanced st506 drivers out for
us, so if we just collected the data for them (the air force has a good listing),
we should be able to write a config option that loads the correct bits.

-John






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