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ashwathgan

SystemC without Signals

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Hi All

 

I tried to implement a simple Task Scheduler in SystemC. It works as follows:

I have three modules "TaskA" , "TaskB" and "CPU". The algorithm works in such a way that the CPU gives full utilization if only one task is present at a time and gives 50% utilization if both the tasks are present. The Arrival times of both the tasks are assigned before the start of the simulation. I was able to implement it with ports and signals, but now i want to measure the performace without ports and signals (i.e) using the C++ and the internal clock of systemc( sc_time_stamp(), sc_start() etc ).

 

Presently, i have the following:

 

class Task : sc_module

{

void taskA()

{

....

bool tskA = true;

if(tskA)

{

eventA.notify(10,SC_NS); // Arrival time of A as a Event

tskA = false

}

else

{

outA= true // So that we get the event after 10ns of simualtion time

}

 

void taskB()

{

.....

bool tskB = true;

if(tskB)

{

eventB.notify(20,SC_NS); // Arrival Time of B as a Event

tskB = false;

}

else

{

outB = true; // To get taskB after 20ns after the start simulation 

}

}

 

SC_CTOR()

{

SC_METHOD(taskA);

SC_METHOD(taskB);

 

sensitive << eventA;

sensitive << eventB;

}

 

 

class CPU: sc_module

{

 

Task A;

Task B;

 

void cpu()

{

 

A.taskA();

B.taskB();

 

if(outA)

{

//Debug statement

 

cout << "A arrives @"<< sc_time_stamp() << endl;

 

some calculation

}

else if (outA && outB)

{

//Debug Statement

 

cout << "B arrives @" << sc_time_stamp() << endl;

 

some calculation}

 

}

}

 

SC_CTOR(CPU) : A("AT"), B("BT")

{

SC_METHOD(cpu);

 

sensitive << eventA;

sensitive << eventB;

}

 

 

But, the problem is the modules gets executed always. To me more precise:

 

What I expect as Output is:

 

A arrives @ 10ns

B arrives @ 20ns

 

 

But, What I am getting now is

 

A arrives @ 10ns

B arrives @ 10ns

A arrives @ 20ns

B arrives @ 20ns

 

I am not able to figure out where I am going wrong, can anyone please give me suggestions/ point out the msitake i am doing here?

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SC_METHOD's and SC_THREAD's are always called once at the start of simulation (to allow reset/startup behavior). If you use dont_initialize() after each registration, you can avoid that:

 

SC_METHOD(my_func);

sensitive << my_event;

dont_initialize();

SC_METHOD(other_func);

sensitive << other_event;

dont_initialize();

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Hi All

 

I tried to implement a simple Task Scheduler in SystemC. It works as follows:

I have three modules "TaskA" , "TaskB" and "CPU". The algorithm works in such a way that the CPU gives full utilization if only one task is present at a time and gives 50% utilization if both the tasks are present. The Arrival times of both the tasks are assigned before the start of the simulation. I was able to implement it with ports and signals, but now i want to measure the performace without ports and signals (i.e) using the C++ and the internal clock of systemc( sc_time_stamp(), sc_start() etc ).

 

Presently, i have the following:

 

class Task : sc_module

{

void taskA()

{

....

bool tskA = true;

if(tskA)

{

eventA.notify(10,SC_NS); // Arrival time of A as a Event

tskA = false

}

else

{

outA= true // So that we get the event after 10ns of simualtion time

}

 

void taskB()

{

.....

bool tskB = true;

if(tskB)

{

eventB.notify(20,SC_NS); // Arrival Time of B as a Event

tskB = false;

}

else

{

outB = true; // To get taskB after 20ns after the start simulation 

}

}

 

SC_CTOR()

{

SC_METHOD(taskA);

SC_METHOD(taskB);

 

sensitive << eventA;

sensitive << eventB;

}

 

 

class CPU: sc_module

{

 

Task A;

Task B;

 

void cpu()

{

 

A.taskA();

B.taskB();

 

if(outA)

{

//Debug statement

 

cout << "A arrives @"<< sc_time_stamp() << endl;

 

some calculation

}

else if (outA && outB)

{

//Debug Statement

 

cout << "B arrives @" << sc_time_stamp() << endl;

 

some calculation}

 

}

}

 

SC_CTOR(CPU) : A("AT"), B("BT")

{

SC_METHOD(cpu);

 

sensitive << eventA;

sensitive << eventB;

}

 

 

But, the problem is the modules gets executed always. To me more precise:

 

What I expect as Output is:

 

A arrives @ 10ns

B arrives @ 20ns

 

 

But, What I am getting now is

 

A arrives @ 10ns

B arrives @ 10ns

A arrives @ 20ns

B arrives @ 20ns

 

I am not able to figure out where I am going wrong, can anyone please give me suggestions/ point out the msitake i am doing here?

 

Hello Sir,

It is all very fine to use explicit event handling with the wait-notify  pair

scheme for small systems with e.g., 5 - 10 events. But what would one

do in a complicated system with e.g., 30 events ? The programmer

would HAVE to correctly add the wait/notify at the correct positions in

the code, else there would be a complete, useless mess. So, why

bother ? With sensitivity lists and implicit events, the SystemC runtime

kernel keeps track of/manages all these confusing but vital event

tracking tasks. Hope that helps.

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