Date   : Sat, 17 Jan 2004 15:14:14 +0000 (GMT)
From   : Andrew Benham <adsb@...>
Subject: Re: Host adapter Issue D

On Fri, 16 Jan 2004, Pete Turnbull wrote:

> On Jan 15, 17:29, Jules Richardson wrote:

> > Oh, the board set from another Torch Hard Disk machine landed on the
> > doorstep yesterday, and it got me curious as it's the first time I've
> > seen the use of an Adaptec ACB4000 board; normally Torch favoured Xebec
> > controllers on their BBC-based machines

This led me on a trip down memory lane. My hard disk system started off
life as a Torch add-on box that was given to me. This certainly included
a Xebec controller. I don't know if the Torch Z80 second processor
I had at one time came from this box, or from elsewhere. It's just a
shame we're not having this discussion 15 years ago!

> Providing you can
> format the disk (that part's slightly different), and can initialise
> the Xebec controller with the drive parameters each time you start the
> machine, the rest works as you'd exect.  The Adaptec ACB4000 series
> store drive geometry on the drive, and read it back as part of their
> initialisation process; the Xebec S1410 has to be given the parameters
> by the host.  When I built my S1410 system for the Beeb, I wrote my own
> formatter, which stored the disk info in a short file on track 0, and I
> wrote a little boot program which extracted that and set up the S1410
> properly.

My solution to this problem with the Xebec controller was to disassemble
their firmware and discover where the default drive geometry was stored
in the EPROM. From memory, the controller defaulted to the parameters
for a standard (at the time) 5MB drive. [ Yes, that's 5MB and not 5GB! ].
I blew a new EPROM with my drive's geometry in it instead, and that was
my operational system for a while.

My motivation to switch to a ACB4000 controller came when I upgraded
my Master 128/512 to Acorn's "Alternative Master 128 System ROM".
This ROM provided ADFS v2.03: this includes a "*VERIFY" command which
verifies floppies =and= hard disks. However, for verifying hard disks
it uses SCSI command 2FH - this SCSI command is not supported by
the Xebec card.

Somewhere or other I probably still have a soft copy of the disassembly
of the Xebec firmware. I also should have my unfinished attempt at
producing ADFS source code (Lancaster University Assembler) starting
from a disassembly of ADFS v2.03
Let me know if you're interested and I'll have a search.

-- 
Andrew Benham     adsb@...       
Southgate, London N14, United Kingdom

The gates in my computer are AND OR and NOT, not "Bill".