Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!apple!sun-barr!newstop!sun!pepper!cmcmanis
From: cmcmanis%pepper@Sun.COM (Chuck McManis)
Newsgroups: comp.sys.amiga
Subject: Re: ESDI controller?
Message-ID: <117093@sun.Eng.Sun.COM>
Date: 21 Jul 89 23:25:20 GMT
References: <339@arnor.UUCP>
Sender: news@sun.Eng.Sun.COM
Reply-To: cmcmanis@sun.UUCP (Chuck McManis)
Organization: Sun Microsystems, Mountain View
Lines: 56

In article <339@arnor.UUCP> kevin@arnor.UUCP (Kevin Goroway) writes:
>Well!? Are there any ESDI controllers available for the amiga?
>A simple 'no' or a simple 'yes' would do just fine, but if the answer is 'yes'
>I would love some information as to where and how much...

First some definitions, there are several levels of drive interface.
LEVEL 1) Drive Control Interface Level (current standards ST-506, ESDI, SMD)
	This interface defines which pins on the connector to the drive
	control stepping the heads, which direction they step, serial
	data to and from the R/W heads, and status information such as
	sector positioning, track 0 detect etc.

LEVEL 2) Storage Device Interface Level (stds SCSI and IPI)
	This interface logically divides a device into blocks of 
	arbitrary size, and establishes a messaging protocol for
	making requests and receiving data and status from a storage
	device. 

LEVEL 3) Host Interface Level (A2090A, HardFrame, SupraDrive, ...)
	This is the buffer interface between the internal interface
	of the host, and one or more Storage Device Interface
	standards. 

Going from Level 3 to Level 1 requires three separate interfaces.
The Hard Disk interface card provides the first, the SDI 
card provides the second, and the DCI card provides the third. 
Any or all of these "levels" can be combined physically on one
interface. For example, the A2090 card interfaces between the 
A2000 Bus interface to the SCSI storage device interface. However
is also provides a translation from the A2000 bus interface to the
ST506 Drive Control interface. On the other side of the coin, the 
Conners SCSI drives provide both the SCSI storage device interface
and the drive control interface on the same drive. 

An example of a three card interface would be :
	A2090 ----(SCSI)---->Adaptec 4000A----(ST506)---> Drive

An example of a one card interface would be :
	A2090 ----(ST506)----> Drive

To use an ESDI drive you would have to setup something like :
	Interface ----(SCSI)---->Adaptec 5000A----(ESDI)---->Drive
(check the adaptec number before ordering it)

There is also a software caveat. When you use an external to the drive
interface board, the board doesn't know ahead of time what kind of 
drive it is talking to in terms of cylinders, heads, etc. You have to
initialize it somehow. Most manufacturers make the board read sector
0,0,0 off the drive for this information on powerup so you only have
to do it once. Anyway, there isn't a solution for that yet except
for some hacks. The hardware is readily available though.

--Chuck McManis
uucp: {anywhere}!sun!cmcmanis   BIX: cmcmanis  ARPAnet: cmcmanis@sun.com
These opinions are my own and no one elses, but you knew that didn't you.
"A most excellent barbarian ... Genghis Kahn!"