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Mr Alfabet

How does SystemC-AMS solve state space equations?

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Basically the question stated in the title, I'm particularly interested in:

  • Does the solver make smaller steps internally than the TDF module time step?
  • If so: are these steps fixed (like 1/100th of the TDF module time step) or variable?
  • Is there a way to find out how many steps the solver actually did?
  • What kind of solver algorithm is used?

If anyone has an answer to one of these questions or can point me to a document that answers them, please tell me. I was not able to find this information in the LRM or through Google.

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The solution of state-space equations is an implementation detail and not covered by the SystemC AMS 2.0 LRM. However, the SystemC AMS 2.0 LRM defines the semantics for the solution of the state-space equation system and how you can obtain solutions with a pace smaller than the TDF time step and redo a solution step (cf. to the discussion of the tstep parameter in clause 4.1.4.5.8).

 

Regarding your points, the answers depend on the used implementation of SystemC AMS 2.0. I will assume that you use Fraunhofer SystemC-AMS:

  • An implementation may do smaller time steps than the TDF module time step.
  • The linear ODE/DAE solver is for its internal time stepping constrained only to not make a step bigger than the TDF module time step or the explicitly passed tstep value.
  • I'm not aware that an instance of sca_tdf::sca_ss can output statistics about its internal time stepping.
  • As far as I know, Fraunhofer SystemC-AMS uses the Euler and trapezoidal integration methods.

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