All,
Ultimately, AMI is a specification of the format and syntax of a .ami file
and what the inputs and outputs are of a DLL. It is important that the model
makers write DLLs in accordance with the standards defines of their inputs
and outputs.
It is not a requirement of an EDA tool follow the flows suggested in the
standard. SiSoft and other companies believe the flow in IBIS 6.1 gives the
wrong answer, as we stated three years ago. SiSoft uses a flow that gives
the correct answer, and submitted BIRD 166 to document this.
If other EDA companies state that they are getting the correct answer
because they religiously execute the flows documented in IBIS 6.1, so be it.
Bottom line is when a customer gets a different results from different EDA
vendors we can point them to this discussion and they can decide who is
right, since we cannot.
Walter
Walter Katz
wkatz@xxxxxxxxxx <mailto:wkatz@xxxxxxxxxx>
Phone 303.449-2308
Mobile 303.335-6156
From: Bob Miller (APD) [mailto:bob.miller@xxxxxxxxxxxx]
Sent: Monday, June 19, 2017 4:05 PM
To: Ambrish Varma <ambrishv@xxxxxxxxxxx>
Cc: wkatz@xxxxxxxxxx; Arpad_Muranyi@xxxxxxxxxx; ibis-macro@xxxxxxxxxxxxx
Subject: Re: [ibis-macro] Re: Response to BIRD-190
If this is the case then I think I can safely say that IBIS-AMI does a poor
job of support for statistical simulation, not to even supply a truly
workable path for adaptation therein, or even a
statistical-after-time-domain flow to patch around it.
Regards,
Bob
On Mon, Jun 19, 2017 at 1:57 PM, Ambrish Varma <ambrishv@xxxxxxxxxxx
<mailto:ambrishv@xxxxxxxxxxx> > wrote:
Hi Bob,
Yes. That is why we have/had Getwave. And the ‘Note’.
Thanks,
Ambrish.
From: Bob Miller (APD) [mailto:bob.miller@xxxxxxxxxxxx ;
<mailto:bob.miller@xxxxxxxxxxxx> ]
Sent: Monday, June 19, 2017 3:54 PM
To: Ambrish Varma <ambrishv@xxxxxxxxxxx <mailto:ambrishv@xxxxxxxxxxx> >
Cc: wkatz@xxxxxxxxxx <mailto:wkatz@xxxxxxxxxx> ; Arpad_Muranyi@xxxxxxxxxx
<mailto:Arpad_Muranyi@xxxxxxxxxx> ; ibis-macro@xxxxxxxxxxxxx
<mailto:ibis-macro@xxxxxxxxxxxxx>
Subject: Re: [ibis-macro] Re: Response to BIRD-190
EXTERNAL MAIL
Ambrish --
I'm sorry to say that "Init was never meant to do these things" is here and
now unworkable, at least for Broadcom -- not only me in my own little corner
but other sister divisions building and supporting statistical-only models,
even if this was the consensus in the past. (was it really??)
Regards,
Bob
On Mon, Jun 19, 2017 at 1:19 PM, Ambrish Varma <ambrishv@xxxxxxxxxxx
<mailto:ambrishv@xxxxxxxxxxx> > wrote:
Walter,
We know that IBIS 6.1 (not BIRD 190) fails to give the right result when
all models have Init_Returns_Impulse=True IF AND ONLY IF when either the Rx2
optimizes itself based on its input impulse response and/or when Rx2 has a
DFE.
The Init was never meant to do these things.
We have a ‘Note’ in the specification that documents it. BIRD 190 merely
reminds the users of the same fact in the Redriver section of the spec.
This issue only appears when there is Optimization in the Init or other non
LTI behavior (for which we have Getwave).
So the solution to this problem can be 1 of these 2:
a. Implement a Getwave (Model implementation) OR
b. Do smart sweeping to minimize the solution space (EDA tool
implementation)
and not change the specification to accommodate each and every permutation
and combination of models and simulation capabilities out there.
Thanks,
Ambrish.
From: ibis-macro-bounce@xxxxxxxxxxxxx
<mailto:ibis-macro-bounce@xxxxxxxxxxxxx>
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx ;
<mailto:ibis-macro-bounce@xxxxxxxxxxxxx> ] On Behalf Of Walter Katz
Sent: Monday, June 19, 2017 12:38 PM
To: Arpad_Muranyi@xxxxxxxxxx <mailto:Arpad_Muranyi@xxxxxxxxxx> ;
ibis-macro@xxxxxxxxxxxxx <mailto:ibis-macro@xxxxxxxxxxxxx>
Subject: [ibis-macro] Re: Response to BIRD-190
EXTERNAL MAIL
Arpad,
I have demonstrated that BIRD 190 fails to give the right result when all
models have Init_Returns_Impulse=True.
If any model has Init_Returns_Impulse=False, then Init processing requires
that EDA tools generate an AMI_Init proxy using AMI_GetWave results, and in
this case BIRD 190 gives the wrong answer.
Ambrish and Cadence have reputably stated that AMI Models should be
Init-Only or GetWave-Only. So for the case that all of the models are
Init-Only then both IBIS 6.1 and BIRD 190 give the wrong answer.
IBIS is clearly deficient for channels that do not have all Dual Models
(except for the terminal Rx).
BIRD 190 only re-affirms the fact that IBIS 6.1 give the wrong answer for
statistical flow in Redriver channels since it requires that the upstream
equalization is applied to the output of Rx2, not the input of Rx2.
Do you disagree with my proof that BIRD 190 and IBIS 6.1 gives the wrong
answer for statistical flow in this case when all of the models have
Init_Returns_Impulse=True?
Does anyone disagree that IBID 6.1 and BIRD 190 give the wrong answer for
statistical flow in this case when all of the models have
Init_Returns_Impulse=True?
Does anyone disagree that BIRD 166 gives the right answer for statistical
flow in this case when all of the models have Init_Returns_Impulse=True?
Does anyone disagree that we should not put into the standard any flow that
WILL give the wrong answer?
If we cannot get agreement on this, we should simply table BIRD 166 and BIRD
190. I think we have clearly document the problems in IBIS 6.1, that the
IBIS 6.1 Redriver flow gives the wrong answer when either the Rx2 optimizes
itself based on its input impulse response and/or when Rx2 has a DFE.
Walter
Walter Katz
wkatz@xxxxxxxxxx <mailto:wkatz@xxxxxxxxxx>
Phone 303.449-2308 <tel:(303)%20449-2308>
Mobile 303.335-6156 <tel:(303)%20335-6156>
From: ibis-macro-bounce@xxxxxxxxxxxxx
<mailto:ibis-macro-bounce@xxxxxxxxxxxxx>
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Muranyi, Arpad
Sent: Monday, June 19, 2017 11:54 AM
To: ibis-macro@xxxxxxxxxxxxx <mailto:ibis-macro@xxxxxxxxxxxxx>
Subject: [ibis-macro] Re: Response to BIRD-190
Walter,
Thanks for your comments. Regarding the last two bullets of your summary,
* The flow in BIRD-166 does allow the Rx2 to optimize itself correctly.
* The flow in BIRD-166 give the right results.
These statements are only true when we have “all Init-Only or Dual models”
in the simulation, as you stated in your introductory sentence. As you may
recall, the discussions we had in the ATM meetings revealed that we did not
think that imposing such requirements on model makers would be feasible.
The discussions also revealed that the proposed solution in BIRD166.x makes
certain other model combinations worse, and as long as those combinations
are allowed, the proposal in BIRD166 is unable to address the conflicting
requirements for all model combinations.
This is why Ambrish ended up submitting BIRD190. It does NOT attempt to
solve the challenges we are facing, it only documents the situation in the
redriver section of the specification so that the reader would be reminded
to the issues at hand.
It seems that in order to solve these problems, we would either have to
have a “full solution” along the lines of Fangyi’s proposal, or allow only
Init-only, GetWave-only or Dual models together with the proposal in
BIRD166, but the latter didn’t seem to be an option based on the discussions
we had in ATM.
I would very much like to make a decision on this soon, since we are
starting
to go around in circles in discussing this topic.
Thanks,
Arpad
============================================================
From: ibis-macro-bounce@xxxxxxxxxxxxx
<mailto:ibis-macro-bounce@xxxxxxxxxxxxx>
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Walter Katz
Sent: Sunday, June 18, 2017 6:24 AM
To: Ambrish Varma <ambrishv@xxxxxxxxxxx <mailto:ambrishv@xxxxxxxxxxx> >;
ibis-macro@xxxxxxxxxxxxx <mailto:ibis-macro@xxxxxxxxxxxxx>
Subject: [ibis-macro] Re: Response to BIRD-190
Ambrish,
Got time to review my response to BIRD 190, and would like to correct what I
wrote. Changes made in line.
Walter
Ambrish,
Can you please comment on the following statements.
This discussion is limited to statistical simulations of Redriver channels
with Tx1, Rx1, Tx2, Rx2 all Init-Only or Dual models.
1. BIRD 190 states:
a. The impulse response of the Rx2 model will not include all of the
effects
of the upstream equalization, and therefore the Rx2 AMI_Init will not be
able to perform an accurate equalization, and therefore to ensure successful
simulations, the user should be allowed to turn off any automatic
equalization in Rx2.
2. As Fangyi so aptly demonstrated, the Rx2 equalization will include two
parts, one is a scaling (LTI) part from a CTLE and AGC, and the second an
additive part (non-LTI) from a DFE.
a. If the part of the upstream equalization that is excluded in the input
to
Rx2 (as specified in IBIS 6.1 and BIRD 190) is convolved with the output of
Rx2, then both the CTLE and DFE equalization will scale this part of the
upstream equalization
b. If this part is not excluded from the input to the Rx2 then only the
CTLE
scales the effects of the upstream equalization.
c. In case 2.a. the DFE is (incorrectly) added twice
3. For those of us that find this argument unconvincing, then consider the
solution space that the user must explore to find a “best” solution if
automatic optimization is disabled as proposed in BIRD 190.
a. Let us assume that the user has set all of the upstream co-efficient to
their optimum setting, and the Rx2 automatic equalization is turned off by
the user in accordance with BIRD-190.
b. How many simulations would the user be required to run to find the
“best”
solution.
i. Case
1
1. Assume that the Rx2 model has the following controls (typical
PCIeG4, IEEE 802.3bj)
a. 10 CTLE settings
b. 10 AGC settings
c. 4 DFE taps each having 10 tap setting
2. The answer is 10^6 simulations
ii. Case 2
1. Assume that the Rx2 model has the following controls (IEEE 802.3
400Gj)
a. 10 CTLE settings
b. 10 AGC settings
c. 14 DFE taps each having 10 tap setting
2. The answer is 10^16 simulations
c. It is a requirement of our customers that our tool determine the AMI
settings that give the “best” solution. Sweeping these setting in the Rx2 as
BIRD-190 requires is unacceptable.
In conclusion:
* The flow in IBIS 6.1 does not allow the Rx2 to optimize itself
correctly.
* The flow in IBIS 6.1 gives the wrong results even when Rx2 optimization
is
turned off.
* The flow in BIRD-190 does not allow the Rx2 to optimize itself
correctly.
* The flow in BIRD-190 give the wrong results even when Rx2 optimization
is
turned off.
* The flow in BIRD-166 does allow the Rx2 to optimize itself correctly.
* The flow in BIRD-166 give the right results.
Walter