11 Rand and Constraint Block +1

Dec 01, 2012 | Constraint Block, Randomize()

Multiple constraint blocks on a variable.The return value of randomize() function.constraint_mode() to turn constraints on/off.

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Multiple constraint blocks on a variable and between variables

The return value of randomize() function.

constraint_mode() to turn constraints on/off.

A continuing intro to the constraint block, we add a second variable/die (value2) and a second constraint that affects the relation of the values.
Using constraint_mode(), we turn the constraints on and off.

using multiple constraint blocks

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module dice_game;

class dice;
   rand int value, value2;

   constraint six_sides { value>=1  && value<=6; 
                          value2>=1 && value2<=6; 
   }
   constraint seven_eleven { ((value+value2)==7) || ((value+value2)==11); }

   function void pre_randomize();      
      $write(" dice ready to be rolled ....");
   endfunction   

   function void post_randomize();      
      $display(" dice roll is now = %0d %0d", value, value2);
   endfunction   
endclass

   initial begin
      dice my_dice;
      my_dice  = new();

      my_dice.constraint_mode(0);      
      my_dice.six_sides.constraint_mode(1);      
      repeat (8) begin
     assert (my_dice.randomize()) else 
       $fatal(" ERROR: Mister SVS, randomization failed, miserably.");   
      end      
   end 

endmodule // dice_game

.
//run command

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irun -sv dice_roll.sv

Aside: Notice my incorrect usage of $fatal in the logfile warning.