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Message started by SureshCh on May 29th, 2018, 10:59am

Title: Spectre convergence issues device loading failed
Post by SureshCh on May 29th, 2018, 10:59am
Need advise or info on the following two issues:
1) While debugging a large circuit for convergence issues, following warning came up: I ran simulation with "spectre +aps +diagnose netlist.scs".
Warning from spectre at time = 4.02112 us during transient analysis `tran'.
   WARNING (SPECTRE-16941): Floating point exception encountered in device loading. This might result in convergence problems during simulation. Check the device model equations for any illegal operations, such as divide by 0 or data overflow.

What device is this warning related to? How to identify.

My circuit has devices with verilog A models. Is there any relation to verilog A models with this warning.

2) tran: time = 5.621 us    (5.62 %), step = 308.3 fs  (limiting signal: I0.I_QP_0.I31.I3.I9.I0.TPCK:gmnode = 7.43315 mV 7.42195 mV 7.5713 mV, stepid = 7119)
       convergence failure at residue: I0.I_QPUMP_0.I7.TP2:gmnode (RESIDUE=161.798 uA REF=7.56877 mA)

What do the 3 values (highlighted portion) indicate?

Title: Re: Spectre convergence issues device loading failed
Post by Andrew Beckett on Jun 2nd, 2018, 6:54am
Which spectre version are you using? I suspect it's a little old because I don't think it reports the diagnose messages like that in SPECTRE161 or SPECTRE171 (it gives more useful information as to what each number means). If reported as you're seeing it, it's not terribly helpful, I agree.

Can you try a recent SPECTRE161 or SPECTRE171 hotfix version?

Regards,

Andrew.

Title: Re: Spectre convergence issues - device loading failed
Post by SureshCh on Jun 3rd, 2018, 9:35pm
Dear Andrew,

Thanks for the reply.

I am using spectre 16.10.567.
Spectre (R) Circuit Simulator
Version 16.1.0.567.isr12 32bit -- 12 Dec 2017

If there is any specific version in 161 and 171 to use, Please let me know.



Thanks!
Suresh

Title: Re: Spectre convergence issues device loading failed
Post by SureshCh on Jun 3rd, 2018, 10:57pm

Andrew Beckett wrote on Jun 2nd, 2018, 6:54am:
Which spectre version are you using? I suspect it's a little old because I don't think it reports the diagnose messages like that in SPECTRE161 or SPECTRE171 (it gives more useful information as to what each number means). If reported as you're seeing it, it's not terribly helpful, I agree.

Can you try a recent SPECTRE161 or SPECTRE171 hotfix version?

Regards,

Andrew.


Dear Andrew,

I have tried with version 17.10.238. Still the warning shows up:
Warning from spectre at time = 6.22759 us during transient analysis `tran'.
   WARNING (SPECTRE-16941): Floating point exception encountered in device  loading. This might result in convergence problems during simulation. Check the device model equations for any illegal operations, such as divide by 0 or data overflow.

Title: Re: Spectre convergence issues device loading failed
Post by Geoffrey_Coram on Jun 4th, 2018, 7:15am
How complicated are the Verilog-A models? I've seen some diode models from a foundry that weren't well formulated; one could get math errors. For a diode, with two terminals, one can easily add a $debug statement to print out values from inside the model. If it's a more complicated Verilog-A model, it might be tedious to print things out and trace down the problem.

Title: Re: Spectre convergence issues device loading failed
Post by SureshCh on Jun 4th, 2018, 7:47am

Geoffrey_Coram wrote on Jun 4th, 2018, 7:15am:
How complicated are the Verilog-A models? I've seen some diode models from a foundry that weren't well formulated; one could get math errors. For a diode, with two terminals, one can easily add a $debug statement to print out values from inside the model. If it's a more complicated Verilog-A model, it might be tedious to print things out and trace down the problem.

Dear Geoffrey,

There are two va models. one is a poly resistor in which self heating is modeled and the other is detailed mosvar model.
I have also looked at a log file inside "netlist.ahdlSimdb" directory and there was a warning (from GCC) "Woverflow" for a data type. But this does not point to any specific variable inside the verilog A code.

Thanks!


Thanks!

Title: Re: Spectre convergence issues device loading failed
Post by Geoffrey_Coram on Jun 11th, 2018, 5:23am
You could replace the poly res with a linear resistor, and conversely replace the mosvar with a linear capacitor, and then see if you still get the problem. (Of course, it could be that it's only the combination that causes problems.)

Title: Re: Spectre convergence issues device loading failed
Post by Andrew Beckett on Jun 17th, 2018, 3:27am
You may be best contacting Cadence Customer Support at http://support.cadence.com so that an Application Engineer can look in detail at your problem by being able to see the netlist and models.

Regards,

Andrew.

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