Ultra SCSI SSWG Minutes
Ravinder S. Shergill
rss at berlioz.nsc.com
Thu Mar 10 14:24:57 PST 1994
To: SFF Reflector, SCSI Reflector
From: Robbie Shergill, National Semiconductor
Subj: Minutes of the Ultra SCSI SSWG
Date: March 10, 1994
Minutes of the Ultra SCSI Special Subject Working Group (SSWG)
of the Small Form Factor (SFF) Committee.
Held on March 2nd, 1994, at Milpitas, California.
Chaired by: Jim McGrath, Quantum Corp.
Hosted by: Jim McGrath, Quantum Corp.
Minutes recorded by: Robbie Shergill, National Semiconductor Corp.
Jim McGrath brought the meeting to order at 9:30 AM and asked each person in
attendance to introduce themselves. An attendance sheet was also circulated.
Name Company e-mail
---- ------- ------
Wally Bridgewater Adaptec wally at adaptec.com
Mike Dreitlein Adaptec ljlamers at adaptec.com
Norm Harris Adaptec nharris at adaptec.com
Shahe Krakirian Adaptec shahe at adaptec.com
Larry Lamers Adaptec ljlamers at adaptec.com
Craig Stuber Adaptec stuber at adaptec.com
Mark Knecht AMD mark.knecht at amd.com
Joseph Chen Cirrus Logic chen at cirrus.com
Bill Gintz Conner n/a
Louis Grantham Dallas Semiconductor grantham at dalsemi.com
Jens Paetau Dallas Semiconductor n/a
Michael Smith Dallas Semiconductor msmith at dalsemi.com
Bill Ham DEC ham at shwsys.enet.dec.com
Ed Kavetsky DPT kavetsky at dpt.com
Ron Roberts Maxtor ron_roberts at maxtor.com
Mike Farhat National Semiconductor farhat at rockie.nsc.com
John Goldie National Semiconductor cjfgsc at tevm2.nsc.com
Steve Ichikawa National Semiconductor tsmisc at eccc.nsc.com
Todd Nelson National Semiconductor ctwnsc at tevm2.nsc.com
Robbie Shergill National Semiconductor rss at berlioz.nsc.com
Mark Jander NCR mark.jander at colospgs.ncr.com
John Lohmeyer NCR john.lohmeyer at ftcollinsco.ncr.com
Harry Mason NCR n/a
Ting Chan Q-Logic t_chan at qlc.com
Jim McGrath Quantum jmcgrath at qntm.com
Brian Davis Seagate (to Gene Milligan)
Steve Finch SSI 5723283 at mcimail.com
Vit Novak Sun vit.novak at sun.com
Pete Tobias Tandem tobias_pete at tandem.com
Kasem Elkhalid TI 4307725 at mcimail.com
Kevin Gingerich TI 4307725 at mcimail.com
Paul Aloisi Unitrode aloisi at uicc.com
Tak Asami Western Digital asami at dt.wdc.com
Jim McGrath briefly described the SFF Committee's objective and its
workings. He then presented the proposed agenda for this meeting. The agenda
was discussed briefly and adopted as follows:
Review of SFF Rules Mcgrath
Objective of this SSWG Mcgrath
Date and Place of Next Meeting Mcgrath
Ultra SCSI (1) Concept Ham
Media Results Ham
Timing Budget Ham
OBJECTIVE OF THIS SSWG:
Jim McGrath reiterated his needs from the Ultra-SCSI specification as
previously stated in his Ultra-SCSI SSWG document. Jim has customer that
need next higher level of transfer rates, and they are primarily interested
in short distance, inside the box connections. So, the cable length can be
traded for speed. Jim knows that there are also other people that want
faster speeds over longer distances, outside the box. Such out-of-box
applications have to be differential; but the short distance, inside-the-box
applications should be kept single-ended for power and cost reasons.
John Lohmeyer raised the issue that he doesn't want this work continuing in
SFF. He pointed out that this work started in X3T10; so why not keep it
Jim McGrath said that he has no problem with that - perhaps the next meeting
in Newport Beach can be a joint SFF/X3T10 meeting. John said that he doesn't
see a need for even that as we should have basic agreemnet today.
Bill Ham pointed out that the SPI-2 project proposal is being prepared as we
speak and Ultra-SCSI transfer rate can be part of it. John Lohmeyer added
that the SPI spec has only one public comment against it and it is from
Lohmeyer on behalf of the committee. It is to include SCAM into SPI. SPI-2
project proposal will be posted to reflector within a few days.
Joe Chen asked about expectations over time. Jim McGrath said that he
doesn't expect complete agreement today because people would want to go home
and analyze. But he does expect this spec to be completed in 3 months'
The next meeting of this SSWG will be held on March 31, 1994. It will be
held at this same location (Crown Sterling Suites Hotel in Milpitas, CA) and
will be hosted by Quantum Corp.
(Note that the next discussion on Ultra-SCSI will take place in the SCSI
working group in Newport Beach, CA, on March 16, 1994).
ORIGINAL CONCEPT AND MEDIA RESULTS:
Bill Ham (DEC) took floor next and quickly went through his original
presentation to X3T10. Key points of his proposal are:
- intended as informative annex to SPI.
- fully backward compatible with current SPI.
- uses exactly the same physical connection.
Bill then presented the results of DEC's lab work. Bills' tester can go up
to 30 mega transfers/sec (MT/s) and uses separate transceiver chips for both
differential (National, DS36954) and single-ended operation (TI: 9-channel,
BICMOS, SPI-compatible with 24-mA active-negation and termination on-board).
The system sweeps across various data-to-clock time values and measures
Bill's differential system operated error-free (millions of transfers) with
data-to-clock times of about 6ns to 40ns at 20 MT/s; and about 6ns to 27ns
at 30 MT/s.
More discussion took place on the single-ended results. With a shielded
cable, 5 ft long, signals look good at 20 MT/s with little jitter and data-
to-clock times of about 7 to 44 ns allowed error-free operation over
millions of transfers. With 1.5m flat-cable, thirteen wires-only stubs on 4"
centers, and driving and receiving at mid-bus, times degrade only to about 8
to 43ns at 20 MT/s. However, when Bill mixed 1.5m round cable with 1.5m flat
cable with its associated stubs, the signal got very bad. The Vol level was
only about 1v and jitter was high. data-to-clock times went to about 14 to
Bill concluded that short distance and controlled rise and fall times appear
to provide a very friendly environment for 20 Mt/s operation. Key question
is "can we control the silicon well enough ?"
(Bill will provide hard copies of his results at the Newport Beach meeting).
Bill Ham outlined a set of "ground zero" assumptions for further discussion:
1. The Ultra-SCSI device will maintain chip timing and other specs that are
as good or better than the present (SPI) spec when operating in a non-ultra
Larry Lamers asked if we are going to allow old devices (pre-SPI) on the
bus? Jim McGrath and Bill Ham are willing to go along with this limitation
2. We have almost a clean sheet of paper once the two devices are in Ultra-
SCSI mode (data transfer).
3. specific areas to look at:
- window around slew rates
- receiver input spec
Larry Lamers mentioned that glich filter requirements have to be
- max assertion level (Vol)
Wally Bridgewater (Adaptec) stated that perhaps the Vol should be
spec'd in an AC way. paul Aloisi (Unitrode) doesn't want to put more
energy into the bus.
He and Bill Gintz (Conner) asserted that the focus should be on the
- setup and hold times
- active negation parameters
- clarifying how timings are defined.
John Lohmeyer asked about any possible emi issues.Bill Ham said that he
hasn't looked at it yet, but older data says that data traffic is not where
emi peaks are.
Ting Chan said that it may not be a concern at 20MT/s but should be
considered for rates above that.
4. Specify narrower chip (system) operational parameters that are needed in
normal office/computer room environment.
5. Chip specs that can be met by at least two siliocn suppliers using
established cost structures - ie, no BC process.
6. Stay with present packaging technology, but pinout changes are okay.
With the above list agreed to, Kevin Gingerich (TI) asked that we narrow
down the system operational parameters before we get into details of
silicon. This was agreed to and Bil Ham prioritized the above list in order
However, the discussion soon moved into skew budget issues.
Bill Ham said that at least two cable manufacturers are telling him that
cable skew (currently 4ns) can be cut to 2ns. Taking 2ns each from cable and
distortion skew, we can gain 4ns in the budget.
The discussion moved into actual operational parameters such as loading and
power supply range until Larry Lamers asserted that we're getting too deep
in; let's back off and look at the skew budget.
At this point, John Lohmeyer presented NCR's proposal on skew budget.
total cable skew = 4ns
tx chip s/h = 12/17
board skew still 1ns at each end
rx chip s/h = 6/11ns
total cable skew = 4ns
tx driver skew = 4ns
rx receiver skew = 5ns
board skew still = 1ns each
tx chip s/h = 16/21
rx chip s/h = 1/6
John asked if differential transceiver skew geting cut in half is okay with
TI and National as this was a hotly debated SPI spec. Kevin Gingerich (TI)
said that this is okay if the environment parameters are okay. John Goldie
(National) said that John's numbers look feasible.
Larry Lamers showed Adaptec's proposed skew budget numbers. Adaptec shows
assertion time degrading by only 2ns from tx to rx side. John Lohmeyer
observed that Adpatec numbers will have trouble when applied to the
General sense of the group was that NCR and Adaptec proposals are close
enough that any differences can be worked out after further analysis. NCR
and Adaptec will bring revised proposals to the Newport Beach meeting.
Larry wanted to discuss the receiver switching points before dissecting the
skew numbers any further. In particular, Adaptec wants to increase
hysteresis to 0.4v and redefine spec measurement points with hysteresis
considerd. Adaptec also wants to eliminate the glitch filtering requirement
if the group agrees to increase hysteresis to 0.4 volts. No one else offered
any objections on these points.
Steve Finch (SSI) drew some timing diagrams that served as basis for further
discussion on timing measurement points. After significant discussion, the
following measurement points were agreed to:
At the receiver and at the driver:
\ | 2.0v -/-
\ v /
\ --------- 1.6v -/-
\ nom. hyst /|
-\- 1.2v --------- / |
\ ^ / |
-\- 0.8v | / |
|\ / |
| --------------- |
|<- min assert time ->|
2.0v -/- \
/ | \
/ | \
/ | -\- 1.2v
/ | |\
/ | | \
/ |<---- min negation time ---->| \
------ ------------------------------------- ------
\ -/- 2.0v \ /
\ /| 1.6v -\- /
\ / | |\ /
Data \/ | | \/
/\ | | /\
/ \ | |/ \
/ \| 1.2v -/- \
/ -\- 0.8v /| \
-----/ |\-----------------------------------/ | \------
|<--- setup time --->| |
--------- | |
\ | |
\ | |
\ | |
\ | |
Clock \| |
1.2v -\ |<- hold time ->|
Rise and fall times were discussed next. Should the spec remain in terms of
10% and 90% points, or should it be changed to specific voltage levels such
as 0.5 volts and 2.5 volts? There was agreement that the current SPI
specification needs to be enhanced in this this area as the 0% and 100%
("full amplitude") voltage levels are not clearly defined.
Paul Aloisi (Unitrode) pointed out that maximum high voltage has to be
specified, if 10/90 % points are used, so that your tr/tf absolute numbers
don't kill the budget.
Robbie Shergill (National) pointed out that the good thing about 10% and 90%
points is that the full transition range, where the greatest slewing takes
place, is covered. Many people agreed that the best thing to do is to
specify the maximum slew rate. Finally, the group agreed on 400mV/ns maximum
on the test circuit. This is roughly the same as the current SPI spec.
Tak Asami (WD) wanted the present load circuit to be changed. All agreed
that this needs to be looked at.
Bill Gintz (Conner) wanted receiver test conditions also to be specified.
All agreed that this needs to be looked at.
Robbie Shergill wanted the System Deskew Delay time to be defined. John
Lohmeyer clarified that this time is defined as half of total skew in system
contributed by the two nodes (other than cable plant).
It was also mentioned that ground voltage offset spec. for the single ended
case should be defined as well and the current RS-422 based spec for the
differential case should be refined.
In the end, the group came up with the following wish-list for further lab
work on Bill Ham's tester:
a. stubs actually loaded with devices (all SPI-compliant, 16-bit devices).
b. receiver a minimum distance (4") away from driver, which is at the end.
c. cable distance of 1.5m and 3m.
d. loaded with up to 16 devices.
The meeting was adjourned at 3:45 PM.
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