Date   : Mon, 05 Jul 2004 10:06:24 +0000
From   : Jules Richardson <julesrichardsonuk@...>
Subject: Re: Acorn Winchester unit

On Sun, 2004-07-04 at 21:44, D.G.van der Pol wrote:
> Op 2-jul-04 om 15:03 heeft Richard Gellman het volgende geschreven:

> Recently, I build a Winchester Host Adapter board because I would like 
> to use some old scsi harddrive to store all my Master stuff on.

nice! From memory, it's not a complex circuit, just a lot of soldering
as you say. (I was only looking at it recently to see if I could use
exactly the same circuit to hang off a PC parallel port in order to
drive an old Omti bridge board - unfortunately the parallel port's just
too lacking in output lines to work directly)

>  As far 
> as I could find, a standard 8-bit scsi drive should work just fine. I 
> have a whole stack of them, ranging from 40Mb till 4 Gb.

I've got a few 9GB full-height Seagate drives here looking for a home,
in case anyone wants monster storage on their beeb ;)

> But now I ran into a very stupid problem: All harddrives I have seem to 
> be formated with 512bytes/sector or more. Most of the bit newer drives 
> can be formatted with 1024 bytes/sector or more, but as the Master uses 
> 256 bytes/sector, I am not able to format them correctly.

Yep, that does sound familiar. I have a feeling it was discussed on
comp.sys.acorn.hardware a few months ago (possibly in relation to later
Acorn machines, rather than the BBC). 

For starters, did Acorn ever sell Winchester units with SCSI drives? Or
were they always ST506 drives with a SCSI-ST506 bridge board inbetween?
I think the ACW always used an Adaptec board (ACB400 if I remember
right), and I have a feeling that's what's in the Winchester unit I
found too.

As ST506 drives have no 'get geometry' command, whatever does the
formatting is going to have to set up the Adaptec board's drive
parameters somehow. (I have a feeling either the Omti or Xebec boards
could be configured in ROM, but the Adaptec ones always need it set up
in software). 

I remember talking to Pete Turnbull about this a while ago (as I was
after a formatter for my ACW, plus I know he's worked with hooking hard
drives up to BBCs in the past. Pete, where are you? :-)

Anyway, my point is that your formatting utilities may be making an
assumption that they're talking to an Adaptec bridge board on the SCSI
bus, not a SCSI hard drive. That may well cause trouble and require you
to actually format your SCSI drive on a different (non-BBC) machine
(e.g. use dd on a Unix system).

> These 
> programs don't seem to care that my drive is using 512bytes/sector but 
> as soon as I start to save data on the drives, I run into problemes 
> that invalid data is read from the disk.

Interesting. That implies that the formatter's actually working - which
surprises me. Unless it's silently failing :)  (or maybe it's just
defaulting to assuming you have a 10MB drive attached and only laying
out the first 10MB of blocks)

Presumably things are getting upset because the host BBC is asking for
block n and the drive is sending 512 bytes rather than 256. At the write
stage maybe it doesn't matter, as the BBC is probably just saying "write
the following 256 bytes to block n" and the drive doesn't care that
that's not a full block. 

If this is the case, maybe someone out there has a hacked ROM that just
throws away the latter 256 bytes on a read. Wasteful, yes, but not too
much of an issue when it's hard to find a SCSI device less than 80MB
these days.

Other option is just to find an Adaptec bridge board and an ST506 drive
(I tend to grab them whenever I can as there's still no easy way of
backing up an ST506 drive except on the original hardware, and working
ones are getting scarce)

cheers

Jules