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AdrianAlter

Simple program problem

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Hey everyone! I'm a total beginner with SystemC as i'm just starting to learn about it; i'm doing a simple program that takes two inputs and either sums or multiplies them depending on the signal i'm asserting.
This is the code:
 

#include <systemc.h>

SC_MODULE( operation ){
  sc_in<bool> clock;
  sc_in<bool> enable;
  sc_in<bool> reset;
  sc_in<bool> mult;
  sc_in<sc_uint<8>> in1;
  sc_in<sc_uint<8>> in2;
  sc_out<sc_uint<8>> out;
  sc_uint<8> val;

  void func(){
    cout << "in1: " << in1.read() << endl;
    if(reset.read() == 1){
      out = 0;
      out.write(val);
      cout << "@" << sc_time_stamp() << " ||RESET asserted. VAL: " << out.read() << endl;
    }else if(enable.read() == 1){
        val = val + in1.read() + in2.read();
        out.write(val);
        cout << "@" << sc_time_stamp() << " || I summed the numbers. VAL: " << out.read() << endl;
    }else if(mult.read() == 1){
      val = val * in2.read();
      out.write(val);
      cout << "@" << sc_time_stamp() << " || I multiplied the numbers. VAL: " << out.read() << endl;
    }else{
      cout << "@" << sc_time_stamp() << " || doing nothing atm" << endl;

    }

  }

    SC_CTOR( operation ){
      cout << "@" << sc_time_stamp() << " || executing new " << endl;
      SC_METHOD(func);
      sensitive << reset;
      sensitive << clock.pos();
    }
};
#include <systemc.h>
#include <and.cpp>

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

  sc_signal<bool> clock;
  sc_signal<bool> reset;
  sc_signal<bool> enable;
  sc_signal<bool> mult;
  sc_signal<sc_uint<8>> result;
  sc_signal<sc_uint<8>> num1;
  sc_signal<sc_uint<8>> num2;
  int i = 0;
  clock = 1;
  operation operation("TEST");
  operation.clock(clock);
  operation.reset(reset);
  operation.enable(enable);
  operation.mult(mult);
  operation.out(result);
  operation.in1(num1);
  operation.in2(num2);
  enable = 1;
  reset = 0;
  mult = 0;
  num1 = 1;
  num2 = 2;
  clock = 0;
  sc_start(10, SC_MS);
  clock = 1;
  sc_start(10, SC_MS);
  

  return 0;
}

And the output:
 


        SystemC 2.3.3-Accellera --- Jun  5 2019 18:17:04
        Copyright (c) 1996-2018 by all Contributors,
        ALL RIGHTS RESERVED
@0 s || executing new 
in1: 1
@0 s || I summed the numbers. VAL: 0
in1: 1
@10 ms || I summed the numbers. VAL: 3

The problem is that at first cycle, VAL is 0, and should be 3, and at second cycle it should be 6.
What am I doing wrong?

Thanks,

Adrian

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Your code is operating correctly; however, you are displaying the results at the wrong time. This is because the write() method of sc_signal is not the same as a simple store operation.

In normal programming, you expect that if you do:

variable = 5;

Then immediately after storing the value into your variable, the variable will contain the value.

You might then assume that the write() of sc_signal is the same. It is not. It takes a small amount of time for the value to be stored. The amount of time is tiny and is refered to as a "delta delay" time. You can cause your program to wait a delta cycle before displaying the result, but it is slightly more complicated because you are using an SC_METHOD style process instead of the SC_THREAD style process.

If you are using C++11 you can replace your cout line with this to see correct answer:

        sc_spawn( [&]{
          wait( SC_ZERO_TIME ); ///< wait one delta-cycle delay
          cout << "@" << sc_time_stamp() <<"(" << sc_delta_count() << ")"
               << " || in1:" << in1.read() << " + in2:" << in2.read() << "= val:" << out.read() << endl;
        });
 

 

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