Err - A reference to a rand variable in an array index is not currently supported in this context

SystemVerilog
, ,
1

Hi,

the below randomization code:

class classifier_lut_cfg extends uvm_object;
rand bit [31:0] cls_out_doq_active_reg;

function void post_randomize ();
int tmp_hw2sw_ring; 
std::randomize(tmp_hw2sw_ring) with {cls_out_doq_active_reg[tmp_hw2sw_ring] == 1;};
endfunction : post_randomize

gives me the following err:
“A reference to a rand variable in an array index is not currently supported in this context”

any solution/other idea of how to rand ‘tmp_hw2sw_ring’ while “cls_out_doq_active_reg[tmp_hw2sw_ring] == 1;”

2

In reply to yakirye:

I’m not sure why you are attempting to randomize a local variable in the post_randomize() function. Why don’t you make tmp_hw2sw_ring a class variable and randomize it with the class constraints?

3

In reply to cgales:

In reply to yakirye:
I’m not sure why you are attempting to randomize a local variable in the post_randomize() function. Why don’t you make tmp_hw2sw_ring a class variable and randomize it with the class constraints?

Hi, this is a very simplified part of the code as there are few reasons for it.
The ‘tmp_hw2sw_ring’ is later used as an assignment to a multidimensional array.

Why, Do you think the err is related to the fact that its a local var?

4

In reply to yakirye:

Without a complete example showing your issue, it’s difficult to make any recommendations.

It seems that you are trying to impose a constraint in the post_randomize() function which needs to be utilized in the main randomize() call. What about the case where cls_out_doq_active_reg is all 0’s? It is impossible to randomize tmp_hw2sw_ring to a valid value if this occurs.

If you post your entire class and what you are trying to accomplish, perhaps a better approach could be provided.

5

In reply to cgales:

In reply to yakirye:
Without a complete example showing your issue, it’s difficult to make any recommendations.
It seems that you are trying to impose a constraint in the post_randomize() function which needs to be utilized in the main randomize() call. What about the case where cls_out_doq_active_reg is all 0’s? It is impossible to randomize tmp_hw2sw_ring to a valid value if this occurs.
If you post your entire class and what you are trying to accomplish, perhaps a better approach could be provided.

‘cls_out_doq_active_reg’ is never zero (by constraint).
the error seems to be related to a kind of a syntax/elab issue.

unfortunally, i can’t provide the entire class as it is too sensitive…

6

In reply to yakirye:

The following works:


class classifier_lut_cfg;
  rand bit [31:0] cls_out_doq_active_reg;
 
  function void post_randomize ();
    int tmp_hw2sw_ring; 
    std::randomize(tmp_hw2sw_ring) with {cls_out_doq_active_reg[tmp_hw2sw_ring] == 1;};
    $display("post_randomize: cls_out_doq_active_reg is %0h, tmp_hw2_sw_ring is %0d", cls_out_doq_active_reg, tmp_hw2sw_ring);
  endfunction : post_randomize
endclass

module testbench();
  classifier_lut_cfg c;
  
  initial begin
    c = new();
    repeat (10) begin
      if (!c.randomize()) $display("Randomize failed");
      else $display("Randomize success");
    end
  end
endmodule

If it doesn’t work for you, you likely have a tool issue and should contact your vendor.