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From: "Rodney W. Grimes" <rgrimes@GndRsh.aac.dev.com>
Message-Id: <199607222102.OAA19362@GndRsh.aac.dev.com>
Subject: Re: SCSI errors and repeated panics
To: amir@neuron.net (Amir Y. Rosenblatt)
Date: Mon, 22 Jul 1996 14:02:19 -0700 (PDT)
Cc: amir@neuron.net, freebsd-current@freebsd.org
In-Reply-To: <199607222049.QAA00424@prozac.neuron.net> from "Amir Y. Rosenblatt" at "Jul 22, 96 04:49:49 pm"
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> > I see justin replied about a kernel bug, but thought I might mention that
> > you did not complete the scsi bus termination description:
> 
> OK -- I re-supped last night and recompiled my kernel.
> 
> > The upper 8 bits are terminated on the 2940UW, if not you have
> > a miss termination on the data<7-15> signals of the scsi bus,
> > please check your SCSI-Select BIOS settings.
> 
> I'm not entirely sure what you mean. 

I mean that if you go into the SCSI-Select BIOS (Hit ^A during system Power
On Self Test (POST) when the Adaptec bios mentions it) and check the settings
of the on board scsi termination.  You will find 3 or 4 options:

   a)  Automatic (I recommend against this setting, the detection logic
       may fail under certain conditions.)

   b)  High/Low Enabled (ie, all 16 bits of the scsi bus are terminated.

   c)  High Enabled (ie, the upper 8 bits of the scsi bus are terminated)

   d)  Disabled.

In your configuration it _must_ be set to c) above... see the diagrams
in the Adaptec manual....

> I've had devices on boith the 8 and 
> 16 bit internal connectors on the card since the first day I brought the 
> machine online back in February.  The only change I've made to the setup 
> is that originally, the 4 gig HP C1533 DAT was at the end of the 8-bit 
> chain and now it's in the middle, with the NEC CD-ROM drive at the end 
> (the termination on both set appropriately as far as I could tell from 
> the manuals).

Humm... I suspect that the HP C1533 DAT drive has active terminators,
ie the resistor value will be 110 ohms, and the NEC CD-ROM is using
passive termination, ie the resitor value will be 220/330 ohm.   I highly
recommend (and the SCSI-II spec just recommends) that you use active
termination with Fast SCSI-II.

> From the outset I'd adjusted the 2940UW's built-in 
> termination to match this configuration as specified in the manual.  
> Furthur advice or clarification would be greatly appreciated, as it 
> started giving me the same errors again a short while ago (I called the 
> guy who was sitting at the console and had him bring prozac [the machine] 
> down for 15 minutes rather than letting it panic and crash).   Thanks in 
> advance,
> 
> 	-Amir


-- 
Rod Grimes                                      rgrimes@gndrsh.aac.dev.com
Accurate Automation Company                 Reliable computers for FreeBSD