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ADEXL - Using initial conditions from a first sim in a second sim

cdonovan

I am trying to shorten some very long transient noise sims I have. Using ADEL I have succeeded in running a 100us transient simulation (simA) which has transient noise disabled. There are loops that need this time to fully settle before any meaningful results are available.

I then use the spectre.fc from this SimA as the readic file in a 2nd simulation, SimB, which is only 5us long with transient noise enabled. Thus simulation time is much reduced and an can examine signal integrity in the presence of noise.

The next step is to repeat this across corners in ADEXL and this is where I have a problem. I want SimA to create the spectre.fc file that is referenced by the readic of SimB.

My first attempt gave an explicit path for the write and read of the spectre.fc, but ADEXL wouldnt run the sims every second sim. I tried using one run with 1 corner setup with all corners specified. I tried expanding the corner into corners with only 1 sim... all to no avail. It wouldnt run them every second one so SimA kept overwriting the spectre.fc file before SimB got a chance to use it.

I tried to fix this by removing the explicit spectre.fc and simply using the default directory in ADEXL - eg: library_name/testbench/adexl/results/data/Interactive.1/1/SimA/netlist/spectre.fc

I then tried to reference this in the SimB using ../../SimA/netlist/spectre.fc but the output log says this file or directory could not be found. I verified the current working directory in the log did say it was in its netlist directory so I don't see why this didn't work.

This forced me to examine calibrated verification appnote which describes chained sims, but it doesn't mention anything about initial conditions... (appNote_Calibrated_Verification.pdf

I'm not sure what to try next. I'd appreciate any suggestions. Perhaps a completely different route, or maybe a way to get my relative reference to the spectre.fc to work?

Thanks,

Colm

Using VirtuosoIC 6.1.6-64b.500.2.1

  • Frank Wiedmann
    Using a relative path like ../../SimA/netlist/spectre.fc is the correct approach. In addition to that, you need to make sure that SimA always runs before SimB for every corner. To achieve this, define an expression like calcVal("anyOutput" "SimA") as an output of SimB (where anyOutput is the name of an output expression for SimA).
  • cdonovan
    Hi Frank, Thanks for that. Forcing the order was the problem... no point in a sim looking for a file not yet created! I don't suppose there is an easier solution to this that allows turning on transient noise after a certain time period? It would be a really handy option.

    Thanks again.
  • Frank Wiedmann

    An easier solution is probably possible. I have never tried it because I use pnoise instead of transient noise whenever possible. The feature is called "dynamic parameters" (see https://support.cadence.com/apex/ArticleAttachmentPortal?id=a1Od0000000nSoyEAE&pageName=ArticleContent). With "spectre -h tran" on the command line, you get the following example:

    Example4: turn On and Off transient noise in time windows.
              tran1 tran stop=0.5u noisefmax=10G noiseseed=1 param=isnoisy param_vec=[0ns 0 100ns 1 500ns 0 ]
    The transient noise is OFF from time 0 to 100ns. Noise is ON from 100ns to 500ns and noise is OFF from 500ns to stop time.

  • cdonovan
    Oh my god Frank! Thank you so much! I have used dynamic parameters before but I didn't realise it could be used for the noise. This is such a simple solution to an otherwise painful problem for me. That's great!

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