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Output of systemC


bocuabeucon

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Hi all,

Suppose I have a Module which has 2 processes (SC_CTHREAD) T1, T2, and a shared signal as the follows:

 

sc_signal<int> a;

void T1() {

   wait();

   while(true) {

      a = 1;

      wait();

   }

}

 

void T2() {

   int b;

   wait();

   while(true) {

      b = a;

      wait();

   }

}

 

The SystemC design is simulated by 2 clock cycles. Suppose that the execution sequence will be (T1,T2,T1,T2). I donot understand why the ouput is (a = 1, b = 0).

Other execution sequences, like (T1,T2,T2,T1) produce the same output.

I think that the output should be (a=1, b=1).

 

Thanks,

 

 

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Hi,

I am very new in SystemC. This example is extracted from a slide, and it does not provide enough information.

However, I guess that the constructor of the module as the following:

 

SC_CTOR(example) {

   SC_CTHREAD(T1, clk.pos());

   SC_CTHREAD(T2, clk.pos());

}

 

Maybe, we can print the value of a and b at the end of the corresponding process.

As I understand, the scheduler of systemC maintains a runnable queue of processes. In this example, T2 always runs before T1, right? Or, the scheduler will randomly pick up one process to be executed.

 

Thanks,

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Scheduling order of processes in the same run phase is random.

It's important to realise that because a is a primitive channel (sc_signal), it doesn't update its value immediately. a will only update after all processes have and reached a wait statement,

 

regards

Alan

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