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From: rlr@alumni.colorado.edu (Roger Rose)
Newsgroups: comp.sys.sgi,comp.periphs.scsi
Subject: Re: < Connecting Fujitsu M2266SA to SGI SCSI (SOLVED) >
Message-ID: <1991May16.145505.26384@colorado.edu>
Date: 16 May 91 14:55:05 GMT
References: <41530@unlisys.in-berlin.de> <41691@unlisys.in-berlin.de> <1991May15.001955.4146@corpane.uucp>
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> I don't know anything about the SGI, but in order to use synchronous
> SCSI, both the controller and the drive have to be willing to do it.
> We purchased a disk drive once that was willing to do synchronous
> SCSI, but since the controller was not willing to do it, we had to
> jumper it off.  ...

If the drive and the host have properly implemented the message system,
you shouldn't have had to jumper this out.  If someone sends a sync
negotiation message to a device that only does async, the recipient
should either reject the message or reply with a zero offset.  The sender
should interpret either of these actions as a request for async.

> I also do not know if you can do both synchronous
> and asynchronous SCSI on the same cable or not.  If not, then all
> drives on the cable AND the controller would have to be willing to
> do synchronous SCSI.

There's no reason not to intermix on a cable as far as the SCSI spec
goes.  In fact, a single target should be able to talk sync to one
device and async to another (and sync with different parameters to a
third) and keep everything straight.  The sync parameters are supposed
to be maintained on a per I_T nexus.   This is necessary even on a
single-host bus, if the COPY command is used to transfer data across
the bus.

-- 

Roger Rose  {rlr@boulder.colorado.edu}