Date   : Wed, 08 Mar 2006 14:42:55 +0000
From   : Fragula <fragula@...>
Subject: 6502s and SASI/SCSI.

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Hi Phil!

Topic forked. getting sick of the old one.

Phil Blundell wrote:

> I've occasionally thought that it would be cute to make a little
> protocol converter board to interface a modern IDE disk to an old-style
> SCSI/SASI bus, for use with the Acorn winchester controller or something
> like that.  Kind of like a contemporary equivalent of the Xebec
> SCSI-ESDI/MFM converters that you used to see back in the day.
Elegant indeed. Worthy of a good airing!

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.. hang on, I'm having one of those memory crisis things..

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'm thinking of basic block ops, not formatting and the like, which I'm
fairly sure are different, both as far as the drive is concerned, and
the commands used by the format utils, before the Common Command Set was
widely adopted. Sure the 1MHz<->SCSI/SASI adaptors varied, but they are
just dumb address decoders, latch arrays, buffers, terminators etc., the
smarts are on the Adaptec/Xebec boards, which are possibly *broadly
speaking* similar, even as far as basic fetch/put block stuff is concerned.

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.

Of course, LUNs are not supported, and only two devices per "bus", which
is a little bum compared to SCSI. I don't know why, but I feel a beeb
deserves at least 2, and maybe 4 "controllers", and that enables RAID5,
ok. *Viable* RAID5, CD/DVD-ROMS etc.

Now ADFS (and the torch software) can use 7 device IDs, and (in theory)
the Adaptec(which I think this is in the manual) and the Xebec(not
known) can each handle 2 MFM drives, each with the same SCSI device ID,
but on LUNs 0 and 1.

So some translation from SCSIID:LUN to "controller:drive" would be
needed. unless things are far more serendipitious than we have any right
to expect, even on a good day.

> Funnily enough the MDFS is also completely silent: it's just the drives
> that make a noise. 
Oooh! That HURT! <groan> Touche!

> At one point I had my MDFS connected to an old
> (ex-Sun4) 5.25" disk pack, which was almost inconceivably loud.
That's why I no longer use my Sun4 machines for seperate mail&web frontends.

> 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?

Cheers!

M.

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