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Overriding constraints

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Using the example below, how can I override the constraints of classes A and B on an instance by instance basis?

For instance, let's say I wanted a1's constraint of VarA0 to be VarA0 > 3 and b1's constraint of  VarB1 to be VarB1

Thanks!


module test();
  class A;
    rand bit [3:0] varA0;
    rand bit [3:0] varA1;

    constraint c0 { varA0 > 1; }
    constraint c1 { varA1 > 2; }
  endclass

  class B;
   rand bit [3:0] varB0;
   rand bit [3:0] varB1;

   constraint c0 { varB0 > 1; }
   constraint c1 { varB1 > 2; }
 endclass

  A a0=new;
  A a1=new;
  B b0=new;
  B b1=new;

initial begin
  if (a0.randomize()==0) begin
    $display("error!");
  end
  if (a1.randomize()==0) begin
    $display("error!");
  end
  if (b0.randomize()==0) begin
    $display("error!");
  end
  if (b1.randomize()==0) begin
    $display("error!");
  end
  $display("a0.varA0=%d",a0.varA0);
  $display("a0.varA1=%d",a0.varA1);
  $display("a1.varA0=%d",a1.varA0);
  $display("a1.varA1=%d",a1.varA1);
  $display("b0.varB0=%d",b0.varB0);
  $display("b0.varB1=%d",b0.varB1);
  $display("b1.varB0=%d",b1.varB0);
  $display("b1.varB1=%d",b1.varB1);
end   
 
endmodule




Originally posted in cdnusers.org by weberrm

  • Hello!

    There are quite a few different ways to change constraints for a specific instance of the class. The easiest way to do it is to use the b1.randomize() with {constraint} notation.

    if (a1.randomize() with { varA0 > 3;})
    $display("a1.varA0=%d a1.varA1=%d", a1.varA0, a1.varA1)
    else $display("a1.randomize error");

    if (b1.randomize() with {varB1 <5;})
    $display("b1.varB0=%d b1.varB1=%d", b1.varB0, b1.varB1);
    else $display("b1.randomize error");

    The with {...} would have to be used each time you invoke randomize for that instance though. Other options are to use external constraint blocks - but those are class-specific. Or you can extend a class and only modify the constraints (overwrite a constraint or add an additional constraint). You also have the option to enable and disable constraints using the constraint_mode() methods.

    I hope that helps a little....

    Kathleen Meade
    (meade@cadence.com)


    Originally posted in cdnusers.org by kameade

  • Attached is a presentation I created for random data generation which includes slides on overriding constraints.

    Tim


    Originally posted in cdnusers.org by tpylant
    generation.pdf

  • Hello Tim, I am a new user for SV & while going thru the forum I found that u have attached a pdf, but that seems to be encrypted and I am unable to open it. Same is the case with "itp_pylant_generation.pdf" posted onto the forum. Is there any special way to open it. Could u plz help me out. Parag parag@txc.stpn.soft.net


    Originally posted in cdnusers.org by parag123

  • Hi,
    I have written a brief article on soft constraints:
    http://www.aceverification.com/Soft%20Constraints%20for%20SystemVerilog.pdf
    Also, you can download Ace Verification's soft constraints for SV at the following link: http://www.aceverification.com/softconstraints_pkg.htm

    Akiva


    Originally posted in cdnusers.org by Akiva

  • Hi,
    I have written a brief article on soft constraints:
    http://www.aceverification.com/Soft%20Constraints%20for%20SystemVerilog.pdf
    Also, you can download Ace Verification's soft constraints for SV at the following link: http://www.aceverification.com/softconstraints_pkg.htm

    Akiva


    Originally posted in cdnusers.org by Akiva

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