How to pass parameter to constrain?

SystemVerilog
1

Hi,
In my verification environment, the mainly different between my cases is constrain, for example:

//==============================================
   class Image;  
    
    rand int width;  
    rand int height;  
    ...
    endclass  

   case 1:  img.randomize() with  { img_width > 100 ; img_height > 100}
   case 2:  img.randomize() with  {img_width < 120 ; img_height > 120}
   case 3:  img.randomize() with  {img_width != 120 ; img_height > 300}

I want to modify the constraint block to be configurable so that I only need to compile once but can run with different constraints.

I have do some try, use variable in constraint_block

   if (!$value$plusargs("WIDTH=%d", img.width)) begin  
       $display("WIDTH argument not provided, using default value 640");  
       img.width = 640; 
   end  
  
   if (!$value$plusargs("HEIGHT=%d", img.height)) begin  
       $display("HEIGHT argument not provided, using default value 480");  
       img.height = 480; 
   end  
   img.randomize() with { img_width > width ; img_height > height}

However, this approach only allows changing the data and not the operator (e.g., “>”). Additionally, it is inconvenient. How can I solve this issue?
Thanks!

2

You probably want to encapsulate the constraint in a separate class.
Try something like this, which should be easier to configure.

class policy_base #(type T=uvm_object);
    T item;
    virtual function set_item(T item);
        this.item = item;
    endfunction
endclass

class policy_base #(type T=uvm_object);
    T item;
    virtual function set_item(T item);
        this.item = item;
    endfunction
endclass

class policy_one extends policy_base;
    constraint c { ... }
endclass

class image extends uvm_sequence_item;
    policy_base #(image)  policy[$];
    function pre_randomize();
        foreach(policy[i])
            policy[i].set_item = this;
    endfunction
endclass

class sequence exntends uvm_sequence;
    image my_image = new;
    policy_one policy_one_item = new;
    policy_two policy_two_item = new;
    my_image.policy = {policy_one_item, policy_two_item};
endclass
3

Thank you for your response. My main goal is to achieve dynamic binding of constraints at runtime, rather than at compile time.

The reason for this requirement is that I frequently need to modify the constraints, and each time, only the constraints are changed while the rest of the sequence remains the same. I don’t want to recompile the entire project for every minor constraint modification, as it is very time-consuming.

If this requirement is met, I would only need to compile my project once and could run simulations with different constraints by passing the constraint expressions during runtime.

4

You may want to look at strategies for separate and incremental compilation of your design and testbench. These are going to be tool specific.