Date   : Wed, 08 Mar 2006 18:27:25 +0000
From   : Phil Blundell <philb@...>
Subject: Re: 6502s and SASI/SCSI.

Hi M.,

On Wed, 2006-03-08 at 14:42 +0000, Fragula wrote:
> Were they not Adaptec ACB-4000's? in the Acron kit? ISTR that's what in
> my ACW. The Xebec is in the Torch box, no?

Oh right, yeah, probably.  The ones I have lying around are Xebec and
Emulex, but I'm not sure exactly where they came from.

> But *maybe* (time to compare notes with everyone else on the list) the
> two SCSI/SASI<->MFM adaptor (where did ESDI come in?) boards are, at
> least as far as ADFS is concerned, "mostly-compatible"?

I think so.  Like you say, the basic "read block" and "write block"
commands are pretty much the same: it's just the more esoteric stuff
that tends to vary.

> IDE, oh soddit ATAPI hard disks, have allegedly evolved (i think it was
> an IBM Deskstar datasheet) to the point they also have limited CCS
> compatibility too, whether that makes translation easy, or in fact
> unnecessary (too optimistic) is another matter.

It probably doesn't make a whole lot of difference, to be honest.  Since
the transports are different you're always going to need some level of
translating intelligence, and once you reach that point it doesn't
matter much whether you are doing SCSI->SCSI bridging or SCSI->ATA
command set translation.

I thought a bit more about the idea of a S(A|C)SI->ATA bridge board
during an idle moment today.  So long as you could live with
asynchronous transfers only (which I think is all the Acorn thing can do
anyway) you could probably do the whole thing with just a single
microcontroller, ATmega165 or some such.  It'd be pretty easy to have
different partitions on the drive show up as individual LUNs, which I
guess is what ADFS would want.

> > Eventually I fiddled the MDFS to make it generate SCSI parity, and
> > replaced the drive with a newer, barely audible, 3.5" one.
> Sounds like bliss. Firmware only?

No, it needed a little hardware mod; that was the PAL thing I mentioned
earlier on.

p.