Draft Minutes of T10 Plenary Meeting #20 - 3/13/9

Norm Harris x2230 nharris at eng.adaptec.com
Wed Mar 26 10:38:46 PST 1997

* From the SCSI Reflector (scsi at symbios.com), posted by:
* Norm Harris x2230 <nharris at eng.adaptec.com>
John Lohmeyer wrote:
> * From the SCSI Reflector (scsi at symbios.com), posted by:
> * John Lohmeyer <John.Lohmeyer at Symbios.com>
> *
> At 03:59 PM 3/25/97 -0800, Jim Mcgrath wrote (in part):
> >
> >     One thing was discussed that could be interpreted as a protocol issue
> >     and could contribute to the driver discussion is an attempt to
> >     introduce a false (i.e. not counted) transistion at the beginning of
> >     a burst to overcome the problem of cleanly switching the lines for the
> >     first transition after a long period of no transitions.  I'd hope that
> >     the working group will consider ideas like that as well as purely
> >     physical layer changes, since I'd like to avoid a transceiver change
> >     if some minor work in the protocol could fix the problem.
> Yes.  Such ideas (and several write precomp schemes) are definitely up for
> consideration.  However, I should also point out that the first pulse
> problem is not associated with driver types.  This problem is a cabling
> phenomenon that occurs with either symmetric or asymmetric drivers.  We
> will have to deal with this issue in Fast-80 regardless of what we decide
> about symmetric drivers.
> I think some people at the last meeting came away with the mistaken
> impression that switching to symmetric drivers would solve the Fast-80
> first pulse problem.  I think the benefit (if any) of switching to
> symmetric drivers occurs at much higher frequencies.  The reason I say 'if
> any' is that the data presented at the last meeting obviously used a single
> vendor's parts.  It is not clear whether this data represents a benefit
> inherent to symmetric drivers in general or just their design.
> John
> --
> John Lohmeyer                 E-Mail: john.lohmeyer at symbios.com
> Symbios Logic Inc.             Voice: 719-533-7560
> 4420 ArrowsWest Dr.              Fax: 719-533-7036
> Colo Spgs, CO 80907-3444    SCSI BBS: 719-533-7950 300--28800 baud
> *
> * For SCSI Reflector information, send a message with
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You are absolutely right that the first pulse problem has nothing to do
with choice of design.  We believe we made it clear to anyone awake at
the time that this issue is independent of driver design choice.   

I want to reiterate...ASYMMETRY is a bad choice regardless.  Putting
bandaids on this thing by trying to introduce clever changes in the
protocol doesn't erase that fact.  The charter of the physical group is
to provide the best possible electrical platform.  You omit the fact
that besides pictures and measurements that we presented math vector
analysis of the phenomenon as well.  And our problem with asymmetry
should not be construed as just a difference in the design philosophy of
I/O cells. There are other issues relating to power and system
integration as well.

The problems under discussion have nothing to do with Adaptec parts
anymore than the previously demonstrated DC offset and first pulse
symmetry effects have to do with not to spec TI and Symbios parts.
Unless you can show otherwise, I'd be careful about making that

Norman H. Harris
Staff Advisory Engineer
Adaptec Inc.
Mission Critical Subsystems Group
691 S. Milpitas Blvd
Milpitas,Ca. 95035
PH: (408) 957-2230
* For SCSI Reflector information, send a message with
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