Re: IBIS Bug57 Re: Minutes, IBIS Teleconference Meeting 7/20

Hi Bob:

I have been following the non-monotonic question and I have a question to ask
regarding to the end points, how does the parser calculate the -5.42V ? I wanted to
know where is the -5.42V coming from?

thanks
Jason Leung

"Four Errors are produced. An example is below

ERROR - Model out_bad: The [Falling Waveform]
      with [R_fixture]=50 Ohms and [V_fixture]=0V
      has TYP column DC endpoints of 0.00V and 2.50v, but
      an equivalent load applied to the model's I-V tables yields
      different voltages (-5.42V and 2.50V),
      a difference of -100.00% and 0.00%, respectively.

The calculated end point of -5.42 is wrong because of the non-monotonic
data.

When the non-monotonic points are commented out, 0 Errors are produced.

The testing routine should check matching voltages starting at the middle
of the I-V tables. Some EDA tools will accept such a model.

The options are (1) fix the text, (2) reduce Error to Warning - so tools
that accept it will work, or (3) accept this as a failure - and reject the
model if the ibischk3 parser is used for the parsing."

Bob Ross wrote:

> Hello LiuWeidong and Lynne:
>
> Let me clarify that the problem in bug57 is
> not the non-monotonic behavior itself. The
> issue is that the waveform endpoint test
> incorrectly fails. The waveform endpoints
> are actually correct, the the non-monotonic
> behavior described in bug57 causes the parser
> itself to not find the correct endpoints. This
> causes the model to fail because we recently
> changed the endpoint test (bug47) to issue
> an Error when the mismatch is greater than 10%.
>
> So a good model may be rejected because of
> the ibischk3 bug. The region where the
> failure occurs however, is not critical
> (e.g., in an extended clamping region where
> no current could possibly flow anyway. The
> easy (3) fix is just to change the current in
> that region to be monontonic. This type of
> change would be on a case-by-case basis
> based on where the problem is.
>
> I suspect that the parser problem is based
> an algorithm that starts at one end of a
> table to find a solution. If the algorithm
> started at the middle to find the solution,
> this would be less of a problem.
>
> See bug57 for a test case and more information:
>
> http://www.eda.org/pub/ibis/bugs/ibischk/bug57
>
> Bob Ross
> Mentor Graphics
>
> Lynne Green wrote:
> >
> > The EDA tools have to be able to use these models, which means the models
> > must pass the parser.
> >
> > A smart user will send the model back to the person who made it, to verify
> > whether the non-monotonicity is "real", before proceeding with simulation.
> >
> > - Lynne
> >
> > At 09:13 AM 7/25/2001 +0800, LiuWeidong wrote:
> > >For the message bellow,
> > >" Even though the model is non-monotonic, it may represent real data"
> > >" (3) ignore this problem and force the user to modify the IBIS file."
> > >" Bob suggested that we work on (1) as a low priority activity. If the
> > >fix is too difficult, then we might consider (3). No one wanted (2). "
> > >
> > >I want to ask:
> > >It seems that a good model maybe is non-monotonic(right or wrong ?),Then
> > >how can we modefy the IBIS file ?
> > >
> > >Thanks,
> > >regards,
> > >LiuWeidong
> > >
> > >----- Original Message ----- >
> > > >
> > > > IBISCHK3 BUG TRACKING
> > > > - BUG57 Non-Mononic Table Causes Waveform Endpoint Test to Fail
> > > > Bob Ross introduced BUG57 by pointing out that if the [Pulldown] and/or
> > > > the [Pullup] table contains non-monotonic data in the clamping regions,
> > > > and
> > > > there are no [Gnd Clamp] or [Power Clamp] tables, ibischk3 gives an
> > > > incorrect Error message.
> > > >
> > > > The non-monotonic data itself causes ibischk3 to calculate the wrong
> > > > endpoint values because the algorithm probably has numerical
> > > difficulties.
> > > > It probably starts its convergence calculation at one end of the table
> > > > rather than from the middle and gets numerically confused with the
> > > > non-monotonic data.
> > > >
> > > > Even though the model is non-monotonic, it may represent real data. Some
> > > > EDA tools will correctly process the model. However, the recently
> > > > implemented Waveform endpoint tests now report an Error instead of a
> > > > Warning, preventing the model to be processed in systems that uses
> > > > ibischk3
> > > > for input model parsing.
> > > >
> > > > Bob suggested classifying BUG57 as Annoying, Low, and Open.
> > > >
> > > > The problem is how to resolve BUG57. The choices are (1) fix the test,
> > > > (2)
> > > > change the Error back to a Warning, or (3) ignore this problem and force
> > > > the
> > > > user to modify the IBIS file.
> > > >
> > > > Bob suggested that we work on (1) as a low priority activity. If the fix
> > > > is
> > > > too difficult, then we might consider (3). No one wanted (2). Stephen
> > > > Peters suggested that a note could be added to the Warning or Error
> > > > message
> > > > to alert the user of a possible reason for the Error Message so that the
> > > > user could modify the model. Bob suggested that because this is a low
> > > > priority bug, it should be investigated after all the other open bugs are
> > > > fixed. Then we can decide how to proceed.
> > > >
> > > >