Date   : Wed, 24 Nov 2010 10:45:42 +0000
From   : philb@... (Phil Blundell)
Subject: Harddisc fakery using a microcontroller

On Wed, 2010-11-24 at 02:19 +0000, Mike Pepper wrote:
> There were two issues I remember, from my last serious work on this,
> (setting up the above mentioned HDD). One was the lack of the ATN line, and
> the other the lack of a parity line. I seem to remember being told, (perhaps
> by JGH), that the parity could be 'fudged' if needed, (by generating it from
> the actual data). 

It isn't really a fudge: the parity is just the one-bit sum of all the
data lines.  The Acorn host adapter doesn't have the circuitry to
generate it for output data but it could easily be added.  Making it
check parity on input data, if you wanted that, would also not be
terribly difficult in hardware terms but there would probably be some
effort required to make the software do anything useful with the
resulting information.

> I do believe 2 devices are possible, was the tape drive on some of the file
> servers on the same SCSI bus as the HDD? 

On the MDFS, yes, but that was genuine SCSI-1 (complete with ATN line I
think) and not SASI.  As far as I remember, none of the Filestores
supported locally attached tape drives.

p.