Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!unix.cis.pitt.edu!dsinc!bagate!cbmvax!jesup
From: jesup@cbmvax.commodore.com (Randell Jesup)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: SCSI-1 vs. SCSI-2
Message-ID: <20250@cbmvax.commodore.com>
Date: 2 Apr 91 06:11:48 GMT
References: <2216@wet.UUCP> <19941@cbmvax.commodore.com> <19967@cbmvax.commodore.com> <2242@wet.UUCP>
Reply-To: jesup@cbmvax.commodore.com (Randell Jesup)
Organization: Commodore, West Chester, PA
Lines: 38

In article <2242@wet.UUCP> pk@wet.UUCP (Philip King) writes:
>In article <19967@cbmvax.commodore.com> jesup@cbmvax.commodore.com (Randell Jesup) writes:
>>	Yup.  We will do synchronous if the drive requests it (quantums can
>>be told to request it: mode select page 55, byte 2, bits 4 and 5).  There may
>>be a battmem bit for it; ask steve.  Some older scsi drive (guess who) will
>>crash and take the bus down with them if asked to do synchronous.

	There apparently isn't such a bit in the driver, unless I missed it.

>Randall, perchance were you referring to ***gate when you alluded to some 
>drives taking the bus down if you requested synchronous?  I have an Imprimis/
>Seagate ST-1239N, which is a 200M 3.5" drive that supports synchronous transfer
>(there's a jumper you add).  I presume that if ***gate was the party in
>question, then my drive should be fine, since it's really originally a
>CDC/Imprimis piece?

	If I've read the source right, the controller won't request sync xfers.
Some drives (like Quantum) allow you to specify that the drive should request
them.  Some drives probably request sync xfers all the time.  It's not a big
issue usually on amigados, depending on how busy your disks tend to be (though
it may well help when backing up to scsi tape).

	Ah, the wonders of supporting such "standard" drives as the ST225N.

>I also wondered if anyone else had any more specific information on how
>to activate my drives read-ahead cache, with the 'mode select' command
>Lee Erickson and Dave were referring to earlier.  Is there a program that    
>allows me issue these commands?

	Keep your eyes open, I've been up late nights...

-- 
Randell Jesup, Keeper of AmigaDos, Commodore Engineering.
{uunet|rutgers}!cbmvax!jesup, jesup@cbmvax.commodore.com  BIX: rjesup  
Disclaimer: Nothing I say is in anything other than my personal opinion.
Thus spake the Master Ninjei: "To program a million-line operating system
is easy, to change a man's temperament is more difficult."
(From "The Zen of Programming")  ;-)