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Hidden States and SpectreRF: Is there a safe way to read DC values from file?

bmar


Beating my head with this problem for some time now.  Any help would be appreciated.

In our top-level test bench we have 84 8-bit registers that we need to set to get the whole thing to start up in a defined state.  These are mostly just trim settings, etc (so they don't change during the simulation).  Originally we used 84 ADE variables and multibits, but these are a huge pain to set (especially because they have to be in base-10 inside ADE).

We already have a text file with all the register settings as hex values.  It would really be best if we could just read this text file in at simulation time.  Ok, here is the catch....I want to use SpectreRF in this simulation.

Here is what I tried:  I don't need AMS (these are just DC values).  So I wrote a verilog-a model instead.  I used $fscanf to read the value into an integer at in @(initial_step).  I then use integer division and modulus to decompose it into a bunch of bits (each bit is of type integer).  I then just assign these with a contribution operator to each of the electrical outputs.  (1 = 1V, 0=0V)  The solution worked great....but...

The problem with this implementation is that there are hidden states.  Clearly I read the file only once at initial_step and so the variables hold this state (=hidden state).  Perhaps I could call $fscanf every time step, but that sounds like a bad solution (slow?).

Any ideas anyone?

Thanks in advance!

Parents

  •  You may also want to check out these articles on Cadence Online Support    http://support.cadence.com

    Article 11187476:  How to turn off hidden state checker when running pss/hb analysis.    

    and

    Article 20384843:  FAQ: SpectreRF Convergence tips for Shooting PSS analysis (Article 20409487 covers the same for HB)

    Verilog A:

    • Models designed with event-driven digital semantics in mind often do not work well in RF analyses.
      • Transient analyses require only the large-signal circuit behavior to be defined. Most RF analyses require that the small-signal behavior also be well-defined and well-behaved.
    • Harmonic balance does not work well with discontinuities of any type, for example “transition” statement.
    • “transition” statement is an issue for all RF analyses. Avoid if possible in RF analyses.
    • “delay” is usually difficult for shooting. Consider removing or replace by lumped approximate element.

    best regards,

    Tawna

Reply

  •  You may also want to check out these articles on Cadence Online Support    http://support.cadence.com

    Article 11187476:  How to turn off hidden state checker when running pss/hb analysis.    

    and

    Article 20384843:  FAQ: SpectreRF Convergence tips for Shooting PSS analysis (Article 20409487 covers the same for HB)

    Verilog A:

    • Models designed with event-driven digital semantics in mind often do not work well in RF analyses.
      • Transient analyses require only the large-signal circuit behavior to be defined. Most RF analyses require that the small-signal behavior also be well-defined and well-behaved.
    • Harmonic balance does not work well with discontinuities of any type, for example “transition” statement.
    • “transition” statement is an issue for all RF analyses. Avoid if possible in RF analyses.
    • “delay” is usually difficult for shooting. Consider removing or replace by lumped approximate element.

    best regards,

    Tawna

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