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From: "Rodney W. Grimes" <rgrimes@gndrsh.aac.dev.com>
Message-Id: <199509010158.SAA13422@gndrsh.aac.dev.com>
Subject: Re: 4GB Drives
To: gibbs@freefall.FreeBSD.org (Justin T. Gibbs)
Date: Thu, 31 Aug 1995 18:58:38 -0700 (PDT)
Cc: FreeBSD-hackers@freebsd.org
In-Reply-To: <199509010057.RAA03740@freefall.FreeBSD.org> from "Justin T. Gibbs" at Aug 31, 95 05:57:02 pm
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> 
> >> Hmm.  Are you sure that the drive will not disconnect even for a short time
> >> after receiving its command?
> >
> >Darn sure, I effectivly disabled disconnect/reconnect by tweaking the
> >buffer full/empty ratios and a few other parameters in mode page 2.
> 
> Why not just turn off disconnections in SCSI-Select? :)

Because I can't do that on an NCR 53C825 :-).

> >> >The data I need is being very difficult to obtain without spending major
> >> >dollars on a scsi bus analyzer and a large logic analyzer :-(.  I guess
> >> >I could go out to the labs some weekend, but it is a pain to check in this
> >> >much equipment.
> >> 
> >> I would think that a scope attached to the led line would be sufficient
> >> for most of the timing.
> >
> >Yes, it should be, but if I have things like command queueing occuring I
> >can not correlate the edge created in the stripe layer with the edge
> >created by the LED, it may be skewed by 1 cycle.  Or I could go get a
> >$10k storage scope and use single events :-).
> 
> You will need to pause the sequencer in order to change the status
> of the led anyway if you do it from the kernel, so the edges should
> be distinguishable between kernel blinks and sequencer blinks.

I well be blinking the controller LED from the sequencer, not the kernel,
I have lots of blinking signals from the kernel, I have 8 x 16 bits worth
of them if I so desire :-).

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