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  • Array constraint

Array constraint

SystemVerilog 6745
Array constraint... 1
UVM_geek
UVM_geek
Full Access
18 posts
May 21, 2023 at 9:20 am

Hi,

In array 2 values should be same between index 0-7.Array elements should be between 1 to 9.
https://edaplayground.com/x/8tmm
OUTPUT is
Result = '{'h0, 'h0, 'h0, 'h0, 'h0, 'h0, 'h0, 'h0, 'h0, 'h0}

Can anyone tell why it is not working?

Thanks !!!

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Solution

Solution

dave_59
dave_59
Forum Moderator
11281 posts
May 21, 2023 at 10:06 am

In reply to UVM_geek:

Your results are all zeros because the randomization failed. You should always test the result of the randomize function.

Your constraints fail because they have a conflict in that an array cannot have 10 unique values between 1-9. Also, constraints must be satisfied before calling post_randomize.

Here is a different approach:

class packet;
  rand bit [3:0] array[10], helper[9];
constraint c1 {
  foreach (array[i]) array[i] inside {[1:9]};
  foreach (helper[i]) helper[i] inside {array};
}
constraint unique_elements {
  unique { helper };
}
 
endclass
 
module test;
  packet p; 
  initial begin
    p=new();
    repeat (10) begin
      assert( p.randomize );
      $display("Result = %p ",p.array); //p.print();
    end
  end
endmodule

— Dave Rich, Verification Architect, Siemens EDA

KillSteal
KillSteal
Full Access
89 posts
May 21, 2023 at 10:07 am

In reply to UVM_geek:

There's a contraint error; meaning that the constraints cannot be solved.

You have a array of size 10, you want them to be between 1 and 9, and unique.
You can only have 9 unique elements based on your above constraints.

An unsolved/error in constraint silver leaves the array as before, and hence the display with all elements in array as 0.

UVM_geek
UVM_geek
Full Access
18 posts
May 21, 2023 at 11:10 pm

Thank you KillSteal for your response.

Hi Dave,
My expected output was {1,2,3,3,4,5,6,7,8,9}or {1,2,3,4,5,5,6,7,8,9}or ......
I mean array size is 10 but it should has unique elements between 1 to 9.As I want 1 repeated set then it should satisfy right?
Please correct me if I am wrong.
"Also, constraints must be satisfied before calling post_randomize."
May be sue to this it got failed as I am making duplicates in the post_randomize().

Thank you Dave for your response.

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