IBIS Macromodel Task Group

Meeting date: 25 June 2024

Members (asterisk for those attending):
Achronix Semiconductor:       Hansel Dsilva
Amazon:                       John Yan
ANSYS:                      * Curtis Clark
                            * Wei-hsing Huang
Aurora System:                Dian Yang
                              Raj Raghuram
Cadence Design Systems:     * Ambrish Varma
                              Jared James
Dassault Systemes:            Longfei Bai                             
Google:                       Hanfeng Wang
                              GaWon Kim
Intel:                        Michael Mirmak
                            * Kinger Cai
                              Chi-te Chen
                              Liwei Zhao
                              Alaeddin Aydiner
                              Sai Zhou
Keysight Technologies:        Fangyi Rao
                              Majid Ahadi Dolatsara
                              Stephen Slater
                              Ming Yan
                              Rui Yang
Marvell:                      Steve Parker
Mathworks (SiSoft):         * Walter Katz
                              Graham Kus
Micron Technology:            Justin Butterfield
Missouri S&T:                 Chulsoon Hwang
                              Yifan Ding
                              Zhiping Yang
Rivos:                        Yansheng Wang
SAE ITC:                      Michael McNair
Siemens EDA (Mentor):       * Arpad Muranyi
                            * Randy Wolff
Teraspeed Labs:               [Bob Ross]
Zuken USA:                  * Lance Wang

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

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Opens:

- Arpad asked whether we should hold a meeting on July 2nd.  Walter moved to
  cancel it.  Ambrish seconded.  There were no objections.  The meeting
  scheduled for July 2nd will not be held.
  
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Review of ARs:

Arpad: Send his C-phy presentation and Alaeddin's to the ATM list.
       - Done.
            
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Call for patent disclosure:

- None.

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Review of Meeting Minutes:

Arpad asked for any comments or corrections to the minutes of the June 18th
meeting.  Ambrish moved to approve the minutes.  Arpad seconded the motion.
There were no objections.

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New Discussion:

SPIM transient support in IBIS:
Kinger reviewed a presentation on a proposal to add more to SPIM (Streamlined
Power Integrity Model) to support transient analysis.  He noted that BIRD223.1,
approved in December of 2023, added SPIM and support for AC impedance and DC IR
drop analyses.  Kinger and Chi-te are now proposing additional information be
added to SPIM to support transient analysis.

[SPIM Transient Target] is a proposed new keyword that contains Vpp, Vmin and
Vmax values.  Kinger said the Vmin is the minimum voltage required for the
circuit to function properly, Vmax defines the upper limit (e.g., a max limit
on overshoot), and Vpp is the peak-to peak-noise that would affect Power Supply
Induced Jitter.

[SPIM icct File] is a proposed new keyword that contains the name of an IBIS-ISS
file and an included subcircuit.  The subcircuit would define the current
profile to be drawn through the PDN.  Kinger said they would like to add VCCS
Poly (polynomial) to IBIS-ISS for this.  Kinger described the stages of
development for the icct model.  He said the 0th order ideal icct profile is
generated by connecting the Silicon model to an ideal voltage source.  The 1st
order modeling involves pulling the icct profile from a PDN model connected to
an ideal voltage source.  The 2nd order approach also pulls the icct profile
through the PDN, but the VCCS used to generate the icct also incorporates the
effects of the voltage drop through the PDN.  To support this second order
approach to the PDN testing, they propose using a VCCS Poly and an I PWL, both
of which would have to be added to IBIS-ISS.  The nominal icct current would be
additionally scaled according to the voltage fluctuation on the power rail.

Arpad noted that these PWL and Poly additions had been discussed on the
reflector this week.  He said that neither of them are currently available in
IBIS-ISS.  He said it probably wouldn't be too hard to add them, but we might
need to ask permission from Synopsys, as the IBIS-ISS is made up of a subset
of their netlist syntax.  Randy said IBIS-ISS (ISS = interconnect SPICE
subcircuit) was originally designed for passive interconnect.  He said that's
why it doesn't include support for these types of devices, and he expressed
concern that people might abuse the definition of IBIS-ISS if we added these
device types.

Arpad, Randy, and Walter suggested that we might instead provide the PWL data
and polynomial definition in the IBIS file (SPIM) and leave it to the EDA tool
to implement the current source and connect it.  Kinger agreed that this
solution might work.

Special characters in the Executable sub-param of [Algorithmic Model]:
Walter said he was aware of one EDA tool that complained about the appearance
of a plus sign ('+') in the Executable sub-param.  Walter noted that everyone
else he'd talked to thought '+' was perfectly legal.  Arpad asked whether the
specification explicitly states anything about it.  Walter said he believed the
specification said that '+' can't be used in a filename, but doesn't prohibit
its use in the Executable sub-param.  Arpad reviewed the specification's
definition of alphanumeric, but he noted that the Executable sub-param is not
restricted to alphanumeric entries.  Arpad reviewed the Usage Rules for
[Algorithmic Model] (IBIS 7.2, pg. 211).  The Platform_Compiler_Bits description
doesn't place any restrictions on the characters, except to state that '_' is
the separator between the three fields.  The Examples include '.' and '-'
characters, and the group agreed that '+' is a legal character in the
Executable sub-param.  Ambrish noted that '+' is also legal in signal_name (IBIS
7.2, pg. 356, Example).

Use of Reserved Words as Model_Specific AMI parameter names:
Walter noted that "Usage, Type, Format ... are reserved names" in the .ami file
(IBIS 7.2, section 10.3.4, pg. 237).  However, other IBIS keywords, for example
"corner", are not explicitly called out as reserved.  Walter said that IBIS 7.2
leaves it to interpretation, and we might want to clear it up and state that
"Corner", for example, can't be used as a Model Specific parameter name.
Ambrish agreed that we shouldn't allow any of the reserved words in IBIS to be
used as Model Specific parameter names.

Arpad reviewed the General Rules for the .ami file (IBIS 7.2, pg. 234), and the
group saw nothing that puts any further restrictions on Model Specific parameter
names beyond the statement on page 237 mentioned by Walter.  Arpad said he had
once seen an AMI model with a Model Specific parameter named "Corner", which
took additional options beyond normal corner values.  Arpad said that if we want
to make it clear we should add a bullet to the General Rules section explicitly
stating that reserved words can't be used as Model Specific parameter names.  He
asked whether anyone wanted to write a clarification BIRD.  Walter said he just
wanted to find out what people thought about the current state of the
specification.  The group agreed that there is no clear answer, but the
specification doesn't seem to restrict the names right now.  Ambrish said that
model makers should exercise some common sense when creating their Model
Specific parameters' names.

T-coil in [C Comp Model]:
Walter noted that it's possible to model a T-coil in an AMI model by providing a
Touchstone file in the Ts4file Reserved parameter.  For a standard IBIS model,
we could use [C Comp Model] to provide the Touchstone file for a T-coil.
However, a T-coil model would require an additional series model connection to
the output, and currently the [C Comp Model] output is always tied directly to
the I/O buffer pad.  Walter said he had drafted a BIRD in 2022 to address this
requirement.  He said the open question is whether we should proceed to work on
that BIRD or wait for a pressing need from the industry.

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

New ARs:

Kinger: Send his "SPIM transient support in IBIS" presentation to the ATM list.

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Next meeting: 09 July 2024 12:00pm PT
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IBIS Interconnect SPICE Wish List:

1) Simulator directives
