Oscillator modeling with SystemC-AMS

[slavisha]

Hello everyone,

I'm trying to model a simple harmonic oscillator with SystemC-AMS by using sca_lsf primitives.

There's no non-linearities in my description. However, I don't get what I expect.

I put everything in the main file.

#include <systemc-ams>

int sc_main(int argc, char* argv[])
{

    sc_core::sc_set_time_resolution(1.0, sc_core::SC_FS);

    sca_lsf::sca_signal in;

    double init_value = 0.0;
    double offset = 0.0;
    double amplitude = 0.0;
    double frequency = 1500;
    double phase = 0.0;
    sca_core::sca_time delay = sca_core::sca_time(0, sc_core::SC_MS);

    sca_lsf::sca_source src("src", init_value, offset, amplitude,
            frequency, phase,delay ); // step of 1 unit at t=10ms
    src.y(in);
    src.set_timestep(1, sc_core::SC_MS);

    
    sca_lsf::sca_signal y_dot1_signal;
    sca_lsf::sca_signal y_dot2_signal;
    sca_lsf::sca_signal y_gain1_signal;
    sca_lsf::sca_signal y_signal;

    sca_lsf::sca_integ  integ1("integ1",1.0,1.0);
    sca_lsf::sca_integ  integ2("integ2",1.0,0.0);
    sca_lsf::sca_gain   gain1("gain1",2.5);
    sca_lsf::sca_add    sub1("sub1");
    

    integ1.x(y_dot2_signal);
    integ1.y(y_dot1_signal);

    integ2.x(y_dot1_signal);
    integ2.y(y_signal);


    gain1.x(y_signal);
    gain1.y(y_gain1_signal);


    sub1.x1(in);
    sub1.x2(y_gain1_signal);
    sub1.y(y_dot2_signal);

    // tracing
    sca_util::sca_trace_file* atf = sca_util::sca_create_tabular_trace_file("oscillator");
    
    sca_util::sca_trace(atf, y_dot2_signal, "dot2");
    sca_util::sca_trace(atf, y_dot1_signal, "dot1");
    sca_util::sca_trace(atf, y_signal, "y");

    std::cout << "Simulation started..." << std::endl;

    sc_core::sc_start(10.0, sc_core::SC_SEC);

    std::cout << "Simulation finished." << std::endl;

    sca_util::sca_close_tabular_trace_file(atf);

    return 0;
  }

The code compiles without any error. But I don't get what I expected. I should have a sinusoidal trace in y_signal, but I don't get it at all.

First of all, is it possible to have a right behavior with SystemC-AMS of this simple harmonic oscillator? Simulink gives me what I expect.

Thank you in advance for your feedback.

Slavisha

[Martin Barnasconi]

sca_lsf::sca_add    sub1("sub1");

Due to this, your feedback is not negative. Either change the gain to -2.5 or replace sca_lsf::sca_add by sca_lsf::sca_sub.

BTW, it is not a good coding practice to instantiate an adder and call it sub1... (difficult to debug)

After this change, it should work

[slavisha]

Thank you very much for you quick reply. It was a copy/paste matter without changing all that was needed.

It does work like a charm now.