Date   : Sun, 21 Dec 1997 16:50:43 +0000
From   : Crispin Boylan <viewtronix@...>
Subject: Hard Drives

For anyone who is interested, here is some more information about this guy
Richard York, in this post from 1992 he describes exactly what would be
compatible with his SCSI card (which is true SCSI and not SASI) as you can
see it is quite interesting as to just how much the board can do! 

Message here:

A few questions have been made about what the SCSI interface card does.
Perhaps now is a good time to describe it a little more fully.
       Firstly Acorn ADFS is 'hard wired' for SCSI device 0. It is
easy to adjust so that is uses a different device, but the fixed device
number remains. Currently multiple drives are supported using the LUN
terminology. This system was chosen because in the days of the conception
of ADFS SCSI drives were very rare. The system instead used SASI (a subset
of SCSI, and infact what SCSI was based on) cards, which drove ST506
drives. This is how part of my system is built, although as I have said
previously I now have a SyQuest drive connected direct to the host card,
ie my SASI to ST506 card (Zebec 1410a for the record) is currently unused.
       Anyway these cards normally supported two drives (normally they
had to be of the same type and size), and the LUN was used to select between
them. Hense drive 0 is SCSI device 0, LUN 0, drive 1 is SCSI device 0, LUN 1
etc.
       I have done some exploritary work on the ADFS with SOLIMON and have
worked out the critical SCSI bus access code, so it COULD be possible to add
support for multiple SCSI drives. However it would not be easy since;
a) ADFS 1.3 is TOTALLY full.
b) SCSI access code is duplicated in several places.
c) How is multiple drive support added? (probably converting LUN to device
   number)

The question however must be asked; WHY whould you want more than one drive??
I certainly can't see any need for it. After all very cheap drives of around
20-40 Meg can be bould, which should be enough for any purpose I can think of.

Don't forget the drive can be partitioned for use with the Master 512, exactly
like with the PC emulator on the Arc. The program is I believe provided with
the 512, but I have a friend who has a program (published in Acorn User) which
allows partitions to be created of arbitary size, which is much better than
the Acorn offering.
       The partition is simply a file of the required size created in the
ADFS file structure, so it doesn't affect the normal ADFS operation at all.

TAPE STREAMER SUPPORT.
In principal it will work, in that the SCSI commands can be sent to the
device,
just as with a normal drive. However tape streamers use a slightly modified
class of SCSI instructions which ADFS I don't think would be able to cope
with.
I suppose a piece of software could be written to create an ADFS filing
system on the tape drive, but it would not be easy. Also the problem of 2
seperately addressable SCSI devices on the same bus would be a problem.

REMOVABLE HARD DRIVES.
These are obviously supported (I'm using one aren't I :-) ), but really this
doesn't mean Acorn went out of their way to do it; just that they look
exactly like a normal drive, except that certain commands respond slightly
differently. For example issuing *BYE spins down the cartridge ready to
eject it. I presume on a non-removable drive the particular command issued
causes the SCSI drive to park its head, though I'm not sure.
       Also I can issue a SCSI command to lock the cartridge and relase it,
though I can't see any benefit in doing this.

GENERAL SCSI NOTES.
Osword &72 is effectively the "issue a SCSI command" OS call, and it works
well. All the above calls (spin down drive etc) can be issued using this
route, just as long as you know what command to issue :-) A SCSI standard
helps!!!


Lots to chew over here. Basically its easy, and fairly foolproof. All you
need is the host card, PSU, SCSI drive and something to put it in.

Anyone who knows the whereabouts of Richard York, if anyone has any
contacts with Solinet, could they please try there - he was technical
consultant at the time of this post, maybe he still is?

Thanks


See ya!
Crispin Boylan
viewtronix@...
http://easyweb.easynet.co.uk/~viewtronix
"If there's a bright centre to the universe, we're on the planet that is
furthest from it" - Luke Skywalker