Design oscillator with enable

[Alaba]

Hello 

I was trying to design an oscillator without using the sc_clock 

 

#include "systemc.h"

SC_MODULE(osc)
{

  sc_in<bool> enable;  
  sc_out<sc_bit> out;
  sc_bit bval;

  SC_HAS_PROCESS(osc);
  osc(sc_module_name name, uint _delay = 0)
      : sc_module(name), delay(_delay)

  {
     //SC_THREAD(run_clk);
     SC_METHOD(run_clk);
     sensitive << enable.pos();
  }  

  void run_clk()
  {
   
    while (enable.read() ==true)
    {
      bval = '0';
      out.write(bval);
      // next_trigger() ;
      next_trigger(20, SC_NS);
      // wait(1, SC_NS);
      bval = '1';
      out.write(bval);
      next_trigger(20, SC_NS);
      // wait(1, SC_NS);
      if (false)  break;
    }
  }

private:
  uint delay;

}; // End of Module counter

And the Test bench

#include "systemc.h"
#include "osc.hpp"
#include <systemc-ams>
int sc_main(int argc, char *argv[])
{
  sc_signal<sc_bit> clks;
  sc_signal<bool> enable;

  osc osc0("osc", 1);
  osc0.out(clks);
  osc0.enable(enable);

  sca_util::sca_trace_file *wf = sca_util::sca_create_tabular_trace_file("clks.dat");
  sca_trace(wf, clks, "clks");
  sca_trace(wf, enable, "enable");

  enable = false;
  sc_start(100, SC_NS);

  enable = true;
  sc_start(100, SC_NS);

  enable = false;
  sc_start(100, SC_NS);

  sca_close_tabular_trace_file(wf);
  return 0;
}

 

I need the clock (oscillator) to start at enable=true and to  stop when enable is false.

I start with enable = false

when enable is changed to true  the sensitivity catches it  

But if it is in enabled  state and  I change input to false  sensitivity wont catch it and gets stuck in an infinite loop. I guess I cant change state once in the while in the loop    

Any solution will be appreciated 🙂 

 

[Eyck]

Declaring run_clk as SC_METHOD and and using a while loop will effectively stop your simulation as time will not progress. next_trigger() will not wait rather trigger the method after the given time.

You should define it as:

#include "systemc.h"

SC_MODULE(osc)
{

  sc_in<bool> enable;  
  sc_out<bool> out;

  SC_HAS_PROCESS(osc);
  osc(sc_module_name name, uint _delay = 0)
      : sc_module(name), delay(_delay)
  {
     //SC_THREAD(run_clk);
     SC_METHOD(run_clk);
     sensitive << enable;
  }  

  void run_clk() {
    if (enable.read() || out.read()) { 
      // executes while enable is active or the out is high. If enable is false it will end with out==false
      out.write(!out.read());
      next_trigger(20, SC_NS);
    }
  }

private:
  uint delay;

}; // End of Module counter

 

[Alaba]

Thanks a lot Eyck.. It works

 // executes while enable is active or the out is high. If enable is false it will end with out==false

  !!!!! Very clever trick 

Thanks again