Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cwjcc!gatech!rutgers!att!lzaz!hcj
From: hcj@lzaz.ATT.COM (HC Johnson)
Newsgroups: comp.sys.atari.st
Subject: Re: Hard Disk Problems
Summary: I think you have it wrong!
Message-ID: <423@lzaz.ATT.COM>
Date: 22 Feb 89 16:56:15 GMT
References: <8902220706.AA01969@ucbvax.Berkeley.EDU>
Organization: AT&T ISL Lincroft NJ USA
Lines: 74

In article <8902220706.AA01969@ucbvax.Berkeley.EDU>, FORTINP@BNR.CA (Pierre  Fortin, P.) writes:
> A while back I wrote about problems adding a second HD unit to my
> SH204...
> 

There is a great deal of chatter here dealing with misconceptions on hard disk
interface.
I will address here only the first four partitions on a hard drive.  I know
that the Supra software adds 8 more, but its not relevant to this discussion.

1. the Atari, Supra, and many ICD interfaces use the Adaptec 4000A scsi to 
	st506 adaptor.  (Atari builds their own under license.).
2. There is only ONE way to format the sectors on the disk. The 4000A is 
	given ONE command (and an optional bad sector list) and it does the
	whole thing.  There is no way for this to differ.
3. There is only ONE way to create GEM partitions on the disk. ATARI's way.
	If not, TOS wouldn't be able to read/write files.
4. GEM and non-GEM partitions are ONLY a way of allocating raw sectors on the 
	disk.  Each partition describes is starting sector and size in the
	partition table found in sector 0 of the hard disk. THIS IS NOT
	SECTOR 0 of C: .
5. Each venders version of ahdi.c does the same thing. It looks for connected
	disks, reads the partition table, and if the partitions name is GEM
	creates a logical disk.  Otherwise it ignores the partition.

OK, so why is there a problem?  Sometimes its hard to tell if a drive is
connected.

6. 	A. ATARI corp, designed the sh204 to have ONE DRIVE on ONE controller.
 		THUS the ATARI ahdi.prg, does NOT TEST for a second drive, even
		tho you can format it.
	B. Unfortunately, there is a nasty bug in the PLA of the SH204 that
		prevents it from reporting errors from the 4000A.  This is
		not a big deal for failed reads or writes, as the 4000A has
		tried and retried; the sector is bad and it will not likely
		be better.
		BUT, when BMS/ICD/SUPRA start polling for connected drives,
		they don't get the error when drive 1 is missing, and screw
		up when they think its there and doesn't work.
		ATARI ahdi doesn't have the problem as it never asks about
		drive 1 on a controller.
7. When a drive is added as drive 1 on a SH204, it is necessary to get someone
	elses driver, as ahdi will not ask if the drive is there.
	AND, most of the other drivers poll for drive 1 and sometimes 2-7
	also, screwing up when the SH204 with 1 drive reports the other ones
	are present also.

WHAT to do.

8. One way, is fix the SH204.  That is what the Berkeley Micro Systems PLA
	does.
	Another, is to patch the supra/icd/bms driver to only ask about drives
	that you have connected. (BMS gave me a patch early on when we didn't
	know what the SH204 was doing to us).
	Another, is disassemble the driver, and change it.  I've done this
	now for my system.

Summary:

a.	Really, all the formatters are equivalent for base formatting and
	creating GEM partitions.

b. 	all the hard disk drivers are interchangeable IF you realize what
	added features are in each one.  This sounds strange, but it means
	that they should all run 1 drive per controller, and the sh204 with
	the pla change.

c. 	ATARI isn't too excited about retro fitting the sh204, In fact they
	dont even believe its a problem.  And for them, it isn't.

Howard C. Johnson
ATT Bell Labs
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hcj@lzaz.att.com