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SystemVerilog Tutorial PART 16: by Abhiram Rao

Examples of Threads in SystemVerilog-1

 

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This is an example of using threads

 


 


program example();

 

// semaphores are a unique datatype in SV semaphore want_to_print;

// this is the "shared resource", would be a bus,

// but in this case its a $display

 

task write_bus(int addr, int data);

     $display("here is a write to the bus at addr %d", addr);

     #100;

endtask

int done = 0, i = 0;

 

initial

  begin

  // here we initialize the semaphore with one token  availabe to      //share. We could initialize

 // with more, if there were an interleaved bus, for  example

 

  want_to_print = new(1);

  fork

   begin

   /// here is one parallel thread competing

    while(!done)

     begin

      // wait for some random time

      #($random() % 100);

      // attempt to get the one semaphore token

      want_to_print.get(1);

      // got it!, lets use the bus

      write_bus(200, $random());

      i++;

      // we must return the semaphore token want_to_print.put(1);

     end

end

 

Here is a second parallel thread

 

begin

  while(!done)

   begin

    // wait for some random time

    #($random() % 100);

    // attempt to get the one semaphore token

    want_to_print.get(1);

    // got it!, lets use the bus to the exclusion of others

    write_bus(100, $random());

    i++;

    // we must return the semaphore token

    want_to_print.put(1);

   end

end

Here is a third (Watchdog) parallel thread, this is to decide when we are done

begin

  while(!done)

    begin

     @(i);

     if (i > 100)

     done = 1;

    end

end

 join

   $display ("done -- out\n");

 end

endprogram

 

 

 

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