Minutes from the 23 May ibis-atm meeting are attached.
The following documents, which were discussed during the meeting, have been
posted to the ATM work archives.
23-JUN-2017 Walter Katz SiSoft BIRD 166.3 Resolving problems with Redriver
Init Flow draft 5 (zip
<http://ibis.org/atm_wip/archive/20170623/walterkatz/BIRD_166_3_Resolving_problems_with_Redriver_Init_Flow_draft_5.zip>
)(docx
<http://ibis.org/atm_wip/archive/20170623/walterkatz/BIRD%20166.3%20Resolving%20problems%20with%20Redriver%20Init%20Flow%20draft%205/bird166.3_draft5.docx>
)
23-JUN-2017 Walter Katz SiSoft BIRD 166 Now - Effects on Keysight Proposed
AMI_Init IR Outputs rev 2 (zip
<http://ibis.org/atm_wip/archive/20170623/walterkatz/BIRD_166_Now_-_Effects_on_Keysight_Proposed_AMI_Init_IR_Outputs_rev_2.zip>
)(pptx
<http://ibis.org/atm_wip/archive/20170623/walterkatz/BIRD%20166%20Now%20-%20Effects%20on%20Keysight%20Proposed%20AMI_Init%20IR%20Outputs%20rev%202/BIRD166.pptx>
)
IBIS Macromodel Task Group
Meeting date: 23 May 2017
Members (asterisk for those attending):
ANSYS: * Dan Dvorscak
* Curtis Clark
Broadcom (Avago): Xingdong Dai
* Bob Miller
Cadence Design Systems: * Ambrish Varma
Brad Brim
Kumar Keshavan
Ken Willis
eASIC: David Banas
Marc Kowalski
Ericsson: Anders Ekholm
GlobalFoundries: Steve Parker
IBM Luis Armenta
Trevor Timpane
Intel: * Michael Mirmak
Keysight Technologies: * Fangyi Rao
* Radek Biernacki
Ming Yan
Maxim Integrated Products: Hassan Rafat
Mentor, A Siemens Business: John Angulo
* Arpad Muranyi
Micron Technology: * Randy Wolff
Justin Butterfield
SiSoft: * Walter Katz
Todd Westerhoff
Mike LaBonte
Synopsys: Rita Horner
Kevin Li
Teraspeed Consulting Group: Scott McMorrow
Teraspeed Labs: * Bob Ross
TI: Alfred Chong
The meeting was led by Arpad Muranyi.
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Opens:
- None.
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Review of ARs:
- None.
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Call for patent disclosure:
- None.
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Review of Meeting Minutes:
- Arpad: Does anyone have any comments or corrections? [none]
- Ambrish: Motion to approve the minutes.
- Walter: Second.
- Arpad: Anyone opposed? [none]
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New Discussion:
BIRD 166.3 Redriver Flow:
- Arpad: Walter has a few slides to share. Let's try to come to some resolution
on BIRD 166 today.
- Walter: [sharing his "BIRD 166 Now, and the Effect on the Keysight Proposal
with AMI_Init Impulse Response Outputs" presentation]
- [slide 2]
- Defines basic topology in question.
- [slide 3] Rx1 has GetWave, Tx2 and Rx2 are both Init-only
- Slide from Fangyi's "Problem_in_BIRD166_Flow" presentation.
- [slide 4] The problem that Fangyi Contemplates
- Fangyi is right. If you do what my BIRD says, and the output of Rx2
Init() contains all of the upstream channel effects, then if you try to
use the output of Rx1 GetWave() and a downstream channel IR
(only containing Tx2, ch2, Rx2) extracted via deconvolution, then you run
into problems.
- I don't interpret the current 6.1 flow as saying to do what Fangyi
described.
- [slides 5, 6, 7] Walter's proposed interpretation of the IBIS 6.1 redriver
time domain flow.
- Step 8a. in the Redriver time domain flow says, " The EDA tool uses the
signal waveform at the output end of Rx1's algorithmic model ... as the
stimulus of Tx2's algorithmic model ... and performs simulation on the
downstream channel ... according to the AMI flow defined ... for channels
without redrivers."
- Step 6c. in the section for channels without redrivers says, "If Tx
GetWave_Exists is false and Rx GetWave_Exists is false, the output of
step 4 (digital stimulus) is convolved with the output of step 3 (output
of Rx Init()) by the EDA tool..."
- Discussion: Walter's proposed interpretation of the interaction between 8a.
and 6c. was as follows. Since the case Fangyi had described had Tx2 and
Rx2 as Init Only, when 8a. referred back to the flow for channels without
redrivers 6c was invoked because the downstream channel was Init Only. He
said this then lead to the assumption that the initial digital stimulus for
the channel should simply be convolved with the output of Rx2 Init(). Walter
noted that this interpretation would mean that all GetWave() functions were
ignored if any model in the chain did not have GetWave(). He noted that
there is no precise way to use the GetWave() functionality of Tx1 and Rx1
if Tx2 and Rx2 are Init Only and one wants to present Rx2's Init() with
all of the upstream effects.
Fangyi/Ambrish/Radek rejected this interpretation. Fangyi said this
interpretation took 8a. out of context. The intent had always been that the
output waveform from Rx1 took the place of a "digital stimulus" to Tx2
for the "channels without redrivers" processing of the downstream channel.
Radek said Walter's interpretation was a bit of a stretch, because in the
IBIS 6.1 flow, the output of Rx2 Init() did not contain any of the upstream
channel's effects (so simply convolving the original digital stimulus with
the output of Rx2 Init() would ignore the upstream channel altogether).
Arpad suggested that if the spec were not clear, and subject to different
interpretations, that perhaps we should start with a BIRD to clarify the
current descriptions. Then we could move on to advancing the flows.
Ambrish and Fangyi rejected this idea and said that the current specification
was clear.
Arpad said he could see it both ways. If the Tx1 and Rx1 also had
Init_Returns_Impulse true, then he could see Walter's interpretation to avoid
double counting. But if Tx1 and Rx1 were GetWave Only, then he could
see Fangyi/Radek/Ambrish's interpretation. Fangyi said the current 6.1
flow never suffered from double counting, because the output of Rx2 only
contained downstream channel information. Arpad countered by asking if we
were trying to solve the issue with the Bob Miller type models that relied
on getting the proper IR to their Init() (for Rx2 in this case). Bob Miller
said that he would prefer we not consider his models as a reason for making
any flow changes. Ambrish reiterated that he didn't want to retrofit the
spec in order to accommodate Bob's type of model.
Ambrish noted the caveat in the time domain reference flow (page 178,
IBIS 6.1):
The Rx executable model file writer should keep in mind that it is not
guaranteed that the impulse response that is presented to the Rx AMI_Init
function will always include the effects of the Tx filter...
Ambrish suggested Bob's models that optimized in Init() and then applied this
optimization in GetWave() did not heed this warning. Bob agreed that the
caveat applied to his models, but noted that the only real effect was that his
models would not be compatible with any upstream model that did not return
an IR from Init(). Bob suggested that instead of merely noting this in
his documentation, it might be better to have a new reserved parameter
so that the model could tell the EDA tool about its requirement. The EDA
tool could then determine when models were incompatible.
- Walter: I think there's fundamental disagreement so we will probably end
up tabling BIRD 166 and not discussing it in the Open Forum.
- EDA tools may simply have to document their own flows.
- I think this was still a very useful discussion to have.
- Arpad: Thank you all for joining.
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Next meeting: 30 May 2017 12:00pm PT
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IBIS Interconnect SPICE Wish List:
1) Simulator directives
