Minutes of SPI-3 Physical Study Group - 1/21/98

John Lohmeyer John.Lohmeyer at symbios.com
Thu Jan 22 20:54:35 PST 1998

* From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
* John Lohmeyer <John.Lohmeyer at Symbios.com>
Minutes of SPI-3 Physical Study Group                          T10/98-111r0

Accredited Standards Committee*
National Committee for Information Technology Standards (NCITS)

                                                   Doc. No.: T10/98-111r0
                                                       Date: January 21, 1998
                                                    Project: xxxx-D
                                                  Ref. Doc.:
                                                   Reply to: John Lohmeyer

To:         Membership of T10

From:       John Lohmeyer, Chair T10

Subject:    Minutes of SPI-3 Physical Study Group
            January 21, 1998 -- Irvine, CA


1. Opening Remarks

2. Approval of Agenda

3. Attendance and Membership

4. Old Business
   4.1 Low-Attenuation Cables (97-213, 97-228) [Rogers, Bellino]
   4.2 Staged Contact Resistance [Amp]
   4.3 Bias Reduction Proposal (97-214) [Bridgewater]
   4.4 Dual Clocking Proposal (97-208) [Bastiani]

5. New Business
   5.1 Initial test results on dual clock signals [Bastiani]
   5.2 Discussion on using eye pattern for specification [Bastiani]
   5.3 Need for error detection on dual-edge clocks [Gintz]
   5.4 Hot plugging concerns [Gintz]

6. Meeting Schedule

7. Adjournment

                              Results of Meeting

1.    Opening Remarks

John Lohmeyer, the T10 Chair, called the meeting to order at 9:00 a.m.,
Wednesday January 21, 1998.  He thanked Skip Jones of QLogic for hosting the

As is customary, the people attending introduced themselves and a copy of the
attendance list was circulated.

2.    Approval of Agenda

The agenda was approved.  Vince Bastiani asked that items 4.4 be deferred
until March. Bob Atkinson (AMP) did not know why item 4.1 was added and asked
that it be deferred until March.

3.    Attendance and Membership

Attendance at working group meetings does not count toward minimum attendance
requirements for T10 membership.  Working group meetings are open to any
person or organization directly and materially affected by T10's scope of
work.  The following people attended the meeting:

         Name          S        Organization         Electronic Mail Address
---------------------- -- ------------------------- -------------------------
Mr. Vincent Bastiani   A# Adaptec, Inc.             bastiani at corp.adaptec.com
Mr. Tak Asami          V  Adaptec, Inc.             asami at itc.adaptec.com
Mr. Wally Bridgewater  V  Adaptec, Inc.             wally at eng.adaptec.com
Mr. Richard Moore      V  Adaptec, Inc.             richard_moore at corp.
Mr. Scott Lindstrom    V  AMP Incorporated          slindstr at amp.com
Mr. Bob Atkinson       O  AMP, Inc.                 rdatkins at amp.com
Dr. William Ham        A# Digital Equipment Corp.   bill.ham at digital.com
Mr. Mike Fitzpatrick   V  Fujitsu CPA               mfitzpatrick at fcpa.
Mr. Sam Ray            V  IBM                       str at almaden.ibm.com
Mr. George Penokie     P  IBM Corp.                 gop at us.ibm.com
Mr. Jay Neer           A  Molex Inc.                jneer at molex.com
Mr. Skip Jones         P  QLogic Corp.              sk_jones at qlc.com
Mr. Ting Li Chan       A  QLogic Corp.              t_chan at qlc.com
Mr. Chuck Micalizzi    V  QLogic Corp.              c_micalizzi at qlc.com
Mr. Fardad Siavoshi    V  QLogic Corp.              f_siavoshi at qlc.com
Mr. Patrick McGarrah   P  Quantum Corp.             pmcgarra at tdh.qntm.com
Mr. Richard Uber       V  Quantum Corp.             duber at tdh.qntm.com
Mr. Daniel (Dan) F.    O  Seagate Technology        daniel_f_smith at notes.
Smith                                               seagate.com
Mr. John Lohmeyer      P  Symbios, Inc.             john.lohmeyer at symbios.com
Ms Yang Jiao           V  TEAC                      yjiao at teac.com
Mr. Peter Baril        V  Temp-Flex Cable Inc.      pbaril at worldnet.att.net
Mr. William McMaken    V  Trimm Technologies        bmcmaken at trimm.com
Mr. Darryl Froman      V  UNISYS Corporation
Mr. Paul D. Aloisi     P  Unitrode Corporation      aloisi at unitrode.com
Mr. Doug Piper         P  Woven Electronics         doug.piper at internetmci.

25 People Present

Status Key:  P    -  Principal
             A,A# -  Alternate
             O    -  Observer
             L    -  Liaison
             V    -  Visitor

4.    Old Business

4.1   Low-Attenuation Cables (97-213, 97-228) [Rogers, Bellino]

Since no one has been present to address these proposals for several meetings,
this agenda item will be dropped.

4.2   Staged Contact Resistance [Amp]

John Lohmeyer briefly reviewed the idea of a staged contact design previously
disclosed by Bill Ham of Digital and documented in the minutes of a previous
working group meeting.  It includes a non-metallic lead-in section that
absorbs the electrical transitions slowly and the mated metallic section of
the contact is low-impedance for in service use.  The idea is that the high-
impedance section charges the contact to the actual bus voltage minimizing the
effects of hot plugging. Bob Atkinson noted that AMP is investigating such a
connector, but he was not prepared to discuss it now.  He asked to defer the
topic until March.

4.3   Bias Reduction Proposal (97-214) [Bridgewater]

Wally Bridgewater asked that this topic be deferred until March.

4.4   Dual Clocking Proposal (97-208) [Bastiani]

Vince Bastiani asked that this topic be deferred until March.

5.    New Business

5.1   Initial test results on dual clock signals (98-113r0) [Bastiani]

Vince Bastiani presented 98-113r0 on initial test results with dual-edge
clocks.  As usual, there were a number of questions about the test setup and
why particular values were selected.  The data supports the idea that dual-
edge clocking is feasible, but more testing is needed and planned.

Several of the test setups involved a relatively long cable from the driver to
a series of closely spaced receivers.  The signals were generally confirmed
previous data where the worst signals were seen at the first receiver and
improved signals at the second and subsequent receivers.  Bill Ham noted that
the idea of a signal "breakwater" ahead of the first real device was a valid
approach that could be realized by adding a simple lumped capacitor.

It was noted that the clock signal used for the test was very regular.  In the
real world, it will not be as regular.

Vince said that he expects to have a test chip before the March meeting.

5.2   Discussion on using eye pattern for specification (98-113r0) [Bastiani]

Vince Bastiani noted that eye patterns might not be entirely relevant to
testing parallel buses because of signal skew.  Bill Ham pointed out that
people who use eye patterns do so because they are forced to use sampling
techniques due to very fast signals.  SCSI does not have this problem since
the signals are still within analog scope ranges and does not need to resort
to using eye patterns.  Using color grade type plots can be valuable for non-
correlated signals to quickly determine the extremes of the waveforms.  This
can look like an eye and could be valuable.

There was some discussion about the term `cable skew' on page 18 of Vince's
presentation.  It perhaps should include other skews beyond just the cable

Briefly, the idea of skew compensation was discussed.  Most people believed
that Fast-80 will not require skew compensation, but we may want to lay the
groundwork for future generations of SCSI.  Skew compensation will require
some protocol changes to provide training patterns.

5.3   Need for error detection on dual-edge clocks (98-144r0) [Gintz]

Bill Gintz gave a presentation (98-114r0) on the need for more robust error
detection mechanisms when hot plugging with dual-edge clocking.  Bill Ham said
that the glitches that Bill Gintz showed were very similar to those  he had
previously measured and presented in March 1997.

There was discussion regarding the probability that the glitches would
introduce any undetected errors.  Bill Gintz was concerned that a plugging
glitch on REQ or ACK could move the clocking point for all the data lines.
This could introduce multiple-bit errors and overwhelm the parity mechanism,
which only reliably detects single-bit errors.

Staged resistance connector contacts is one solution to the plugging glitches.
It works by spreading out the energy of the plugging event.  Adding a CRC to
SCSI is another solution.  It doesn't prevent the glitches, but it would more
reliably detect the errors.

It was noted that there are other mechanisms (e.g., firmware errors, ESD) that
are more likely to produce undetected errors.  Adding a more robust error
detection scheme would help with some of these mechanisms, but not others.
John Lohmeyer noted that adding CRC would impact development costs, but should
have little or no impact on product costs; a staged contact would likely add
cost to each connector.

Bill Gintz said he had a test setup that allows him to inject a short pulse
anywhere within a data pattern provided he has control of the system clock.
This is quite useful in testing for worst-case timing shifts due to plugging

Bill Ham noted that some rather unexpected mechanisms might be present during
plugging events.  He has observed some data that might be explained by high
current densities melting the contact point.  He mentioned an article he had
written in the Digital Technical Journal, December 1997 issue, on this topic.
Bill plans to bring copies of the article to the March meeting.

5.4   Hot plugging concerns [Gintz]

See 5.3, above.

6.    Meeting Schedule

The next meeting of SPI-3 Working Group will be March 16, 1998, in San Diego,
CA at the Hyatt Islandia Hotel (619-224-1234), hosted by QLogic.

7.    Adjournment

The meeting was adjourned at 11:55 a.m. on Wednesday January 21, 1998.

John Lohmeyer                  Email: john.lohmeyer at symbios.com
Symbios, Inc.                  Voice: +1-719-533-7560
4420 ArrowsWest Dr.              Fax: +1-719-533-7036
Colo Spgs, CO 80907              BBS: +1-719-533-7950

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