[Wylug-help] SCSI Parity

[Graham Whaley]

James,
  I don't know about turning the parity off, but something to watch out for
is cable lengths.  As the SCSI frequency ramps up (5/10/20 Mhz), the maximum
cable lengths (for the whole chain) drops.  So, on your O2, which runs 20Mhz
Ultra wide SCSI I think, the maximum cable length is 1 Metre.  That is for
all devices added up on a single chain.  I had to hand build a 500cm cable
to get an external Ultra wide drive to work on an O2.  Interestingly, the
errors I saw included parity errors.  Problems only turned up when we were
'hammering' the O2's drive.  It booted and ran fine until we tried to do a
major compile.

  Just something to be aware of if you are plugging a old and slow device
(5Mhz, standard SCSI-1) into a faster machine.

  If you really need some more info then I have the official SCSI-2 spec
laying around here somewhere.

  While we are here, anybody want some old 2Gig SCSI drives?  Might have a
set of 4 matching ones if anybody wants a 6/8 gig raid.  Otherwise they will
get scrapped one day.

	Graham

> -----Original Message-----
> From: James Holden (Wylug) [mailto:wylug at jamesholden.net]
> Sent: 19 November 2003 09:22
> To: wylug-help at wylug.org.uk
> Subject: [Wylug-help] SCSI Parity
>
>
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> Hi all,
>
> I posted this message to Usenet recently, and wondered if any WYLUG
> minds might have any ideas.
>
> To keep it on topic, I'm not averse to connecting the printer
> to a Linux
> box with an Adaptec 1540 board I have laying around, if I can disable
> parity checking on that.
>
>
> Here goes with the original message.........
>
> I'm trying to find a way to disable parity checking on the SCSI
> interface on one of my SGIs. An odd request, I know, but I have a
> device which appears to generate bad parity and I want to get it
> connected. I don't care if I have to connect it to my Indy, Indigo2,
> O2 or even my old R3000 Indigo.
>
> The device is an Alps MD-2010 dry ink printer. I get parity errors
> when the bus is probed on power up. My bad parity theory is drawn from
> this Usenet thread:
>
> http://groups.google.com/groups?selm=7e7713%2450j%241%40nnrp1.
dejanews.com&oe=UTF-8&output=gplain

Some guy couldn't get a similar printer working on an Adaptec card in
a G3 mac. It seems that the onboard SCSI interface on older macs
ignores parity, to the Alps' brokenness doesn't bother it.

I suppose I could put together a device to do the parity for the
printer out of discretes, but it'd be a long shot. Some XORs and
tristate buffers should work. Anybody got any good reasons why it
wouldn't?

If I get the printer talking on the SCSI bus, I'm pretty certain that
it'll work with CUPS, which supports the printer and supports SCSI
printers.

Help!
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