IBIS Macromodel Task Group

Meeting date:27 July 2021

Members (asterisk for those attending):
Achronix Semiconductor:       Hansel Dsilva
Amazon:                       John Yan
ANSYS:                      * Curtis Clark
                            * Wei-hsing Huang
Cadence Design Systems:     * Ambrish Varma
                              Ken Willis
                              Jared James
Google:                       Zhiping Yang
Intel:                      * Michael Mirmak
                              Kinger Cai
                              Alaeddin Aydiner
Keysight Technologies:      * Fangyi Rao
                            * Radek Biernacki
                              Ming Yan
                              Todd Bermensolo
                              Rui Yang
Luminous Computing            David Banas
Marvell                       Steve Parker
Micron Technology:          * Randy Wolff
                              Justin Butterfield
Missouri S&T                  Chulsoon Hwang
Siemens EDA (Mentor):       * Arpad Muranyi
SiSoft (Mathworks):         * Walter Katz
                              Mike LaBonte
Teraspeed Labs:             * Bob Ross
Zuken USA:                  * Lance Wang

The meeting was led by Arpad Muranyi.  Curtis Clark took the minutes.

--------------------------------------------------------------------------------
Opens:
  
- None.

-------------
Review of ARs:

- Walter to send BIRD213.1 draft 2 to ATM for people to review.
  - Done.

--------------------------
Call for patent disclosure:

- None.

-------------------------
Review of Meeting Minutes:

Arpad asked for any comments or corrections to the minutes of the July 20th
meeting.  Michael moved to approve the minutes.  Walter seconded the motion.
There were no objections.

-------------
New Discussion:

BIRD211.3 draft2:
Fangyi shared the draft.  Ambrish said he had read about half of it, and he had
comments.

Ambrish said, the Definition of the Issue section states that,
  "The current Redriver statistical simulation flow is known to have the
   following issues:"
   
However, three issues are then listed, and the third one affects time domain
simulations not statistical simulations.  Arpad and Fangyi suggested removing
the word "statistical" from the introductory sentence.  Radek agreed, and
Ambrish said this would resolve the problem.

Top of Page 4:
Ambrish said the "(column 1)" was not needed in item 1.  The group redid the
wording of item 1 for clarity.

Ambrish said only the first sentence of item 3 should remain.  He said the
last two sentences were just attempting to summarize information that is
already provided in the Usage Rules of Tx_Impulse_Input.

Bob said that references to page numbers should be removed, as this BIRD will be
relative to 7.1, and we don't yet have that finalized.  In addition, he said the
page numbers weren't necessary since the BIRD describes where things should be
inserted relative to existing sections.

page 6:
In the system simulation figure near the top of the page, Ambrish noted that the
word Channel should not appear at the far left of the figure.  Fangyi added a
note to remove the left-most "Channel" from the figure.

page 7:
Normal (non-repeater) flow descriptions:
Ambrish asked whether the changes in the statistical and time domain flows for
the normal channel had actually amounted to any changes in results.  He said
that step 2 in both the statistical and time domain flows, which deals with the
values of Tx_Impulse_Input, isn't adding anything for the normal flow.  Fangyi
agreed that for a normal flow the results don't change.  Arpad said we had
needed to apply the new parameter description to the normal flow to explain how
it affects old models.  Curtis said we had decided to treat the terminal Tx and
the Redriver Tx in exactly the same way.  Ambrish said all the new steps and
discussion of Tx_Impulse_Input amount to nothing in the normal flow.

Ambrish said that nothing really changes in the normal flow.  He said we should
tell EDA tools to simply ignore the new Tx_Impulse_Input parameter for a
terminal Tx, as it doesn't add any value.  Fangyi agreed that we could do that.
He said we already state that if the parameter is not present, the default is
assumed to be "Downstream".  Fangyi added a note to the draft indicating that
we should keep the original flow and add a statement about the new parameter
being irrelevant to the normal flow.  Ambrish said he would prefer not to change
any language in the specification if we don't have to.

page 8:  Normal time-domain flow
Ambrish said steps 3 through 5 contain discussion about the ways an EDA tool may
determine the model's equalization response if GetWave_Exists is false.  He noted
that the 7.0 specification explicitly stated the conditions under which double-
counting could be an issue and deconvolution might be needed (if the Tx's
GetWave_Exists is True, and the Rx's GetWave_Exists is false, then you might
double count the effects of the Tx since they are contained in the input and
output of the Rx's AMI_Init and would also be in the Tx GetWave's output).  He
said the new language mentions determining the Tx model's equalization response,
but we don't have a problem generating results at the Rx if the Tx is Init-Only
(GetWave_Exists is false).  The new language also fails to explicitly describe
the actual problem scenario.

Ambrish said we should not change the normal flow at all.  We should only add
the additional statements about how the tool can use the "unit impulse response"
dummy aggressor column to determine the filter's response.  He noted that even
this is only necessary for the Rx.  There is never a need to for the tool to
determine the Tx filter's response to get the right answer at the Rx.  Fangyi
agreed that we could revert to the 7.0 descriptions for the normal flow.  He
said the Redriver flows that need the new steps and parameters have all of the
steps independently stated and do not rely on references to the normal flow.  He
noted that EDA tools could always safely utilize the unit impulse response dummy
crosstalk column with Tx models, because no Tx model would optimize based on
crosstalk columns, as no physical Tx device would be aware of its aggressing
effects onto others.

Arpad asked if anyone objected to adopting Ambrish's suggestions.  There were no
objections.  Fangyi agreed to revise the BIRD draft accordingly.

PAMn BIRD213 discussion:
Walter briefly reviewed the fundamentals of the BIRD.  He said the goal was to
avoid the need for a new BIRD and new separate parameters for each new
modulation level, n, we wanted to support.  The proposal defines Format Table
parameters for thresholds, offsets, etc., and these can be of varying lengths
to support different modulations.

Walter noted that the major debate last week had been about PAM_Mapping_Name
and PAM_Mapping_Table.  He said Ambrish had suggested that we remove everything
related to mapping and assume the EDA tool is responsible for knowing what to
do for each type of interface.  Ambrish agreed with this summary.  Walter said
he had no problem with the suggestion, and he proposed that we consider a motion
at the next meeting to remove the mapping information altogether.

Arpad asked whether we could create an Out parameter so the model could tell the
EDA tool what mapping to use.  Walter said the model only knows that it has n
levels and likely doesn't know about the mapping.

Fangyi asked whether this BIRD limited the model to supporting one value of n.
Walter said the parameters were allowed to be Usage Out, so the model could
return dynamically sized tables for different values of n.  The number of rows
in a table is dynamic, but the number of columns in each row is not.  So, the
model could return n rows, each with a single column value.  Fangyi suggested
the specification should mandate that the number of rows in the Output table(s)
match the value of n.  Ambrish asked whether the threshold parameter should be
required.  He said EDA tools could have ways to figure out thresholds
themselves.

- Randy: Motion to adjourn.
- Ambrish: Second.
- Arpad: Thank you all for joining.

AR: Walter to send BIRD213.1 draft 3 to ATM for people to review.
AR: Fangyi to create BIRD211.3 draft 3 based on discussion in today's meeting.

-------------
Next meeting: 03 August 2021 12:00pm PT
-------------

IBIS Interconnect SPICE Wish List:

1) Simulator directives
