Some people put PAM4 parameters in Model_Specific, where the rules for them
are not checked. But tools should also then ignore them with respect to
their special meanings. Move on with a Range into Reserved_Parameters
though, and you get errors like this from ibischk6:
E4627 - Illegal Format Range specified for PAM4_UpperThreshold
I have trouble imagining how helpful it would be to allow more formats for
Out parameters. This is weighing the probability that a model will be coded
with incorrect calculations against the probability that the model maker
will put the wrong data in an AMI file. And if there is any complexity to
the numerical space that simple limits on each parameter can’t express, the
checks would have to widen the space and allow some illegal value
combinations through. For example, the ranges for the three PAM4 thresholds
.might overlap, so if a model produces lower values greater than the center
value, that might not be flagged as an error based on AMI setting alone.
Mike
From: Bob Miller (APD) [mailto:bob.miller@xxxxxxxxxxxx]
Sent: Tuesday, November 01, 2016 5:57 PM
To: Curtis Clark
Cc: Mike LaBonte; IBIS-ATM
Subject: Re: [ibis-macro] Re: Draft Format and Usage Out Clarifications BIRD
I was recalling my usage from memory; it was actually the threshold
parameters, not the offset parameters which were problematic.
I was doing this in the ami file:
(PAM4_UpperThreshold (Usage Out)(Range 0.33 0.0 1.0)(Type Float)
(Description "The decision level for the upper PAM4 eye")
)
(PAM4_CenterThreshold (Usage Out)(Range 0.0 -1.0 1.0)(Type Float)
(Description "The decision level for the center PAM4 eye")
)
(PAM4_LowerThreshold (Usage Out)(Range -0.33 -1.0 0.0)(Type Float)
(Description "The decision level for the lower PAM4 eye")
)
The EDA tool which did not send these parameters to the model, upon
receiving no values for the threshold parameters from the executable model,
quietly used {0.33,0,-0.33} for the trio. But the intention was for the
model to return these values to the EDA tool based on other hardware tap
settings and adaptation thereof.
Another popular EDA tool (the one I originally regressed the model on) sent
these Usage Out parameters to the model in the parameter string and the
model dutifully returned the real values to the EDA tool.
One could legitimately argue that I "got what I deserved." But perhaps a
little clarification in IBIS-AMI is in order.
Regards,
Bob
On Tue, Nov 1, 2016 at 3:27 PM, Curtis Clark <curtis.clark@xxxxxxxxx> wrote:
My guess is that Bob was referring to the default value that is given in the
spec (0.0) for use when that parameter is not declared in the .ami file at
all.
Is that right Bob?
Thanks,
Curtis
On Tue, Nov 1, 2016 at 5:23 PM, Mike LaBonte <mlabonte@xxxxxxxxxx> wrote:
The only allowable data Format for many Reserved_Paramneters including the
PAM4 Lower/Center/Upper ones is Value, and Default is illegal for Format
Value. So technically there should have been no Default to use, but there
should have been some kind of Value in the AMI file that a tool could use
when the model does not output it.. However, since IBIS says “For Usage Out,
the value in the AMI parameter leaves are determined by the Algorithmic
Model.” (oops, grammatical error), I don’t think tools should be silent
about substituting anything. Some people put unusable Values like “NA”,
attempting to cause a flag to be thrown on the play if it isn’t replaced.
Mike
From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Bob Miller ;(Redacted
sender "bob.miller" for DMARC)
Sent: Tuesday, November 01, 2016 5:05 PM
To: Curtis Clark
Cc: dmarc-noreply@xxxxxxxxxxxxx; Walter Katz; Mirmak, Michael; IBIS-ATM
Subject: [ibis-macro] Re: Draft Format and Usage Out Clarifications BIRD
The model maker can specify Usage InOut if that's the behavior they want,
right?
