Enum type generation with distributed wight

SystemVerilog
,
1

Hi all,

I have a constraint for an enum field in my packet class.

it is something like that

typedef enum {
	No_error,
        ERR1,
        ERR2,
        ..
        ..
        ERR20              	      
} Error_t;

I would like to have a distribution of lets say 25% “no_error” packets and all other options to be uniformly distributed.

my question is, is there a way to implicitly say “all other options” ?
something like -

constraint Error_Type_c {Error_Type dist {
No_error :=25,
**??all other options ??:/**75;}

I don’t want to list explicitly all enum options (let say in the future I would extend the enum type and might forget to update the dist constraint and a value can be left out of generation)

thanks in advance ,
Guy

2

In reply to guy.levi:

The best way to do this is to create a random error mode bit and put the distribution on that bit.

rand bit error mode;
rand Error_t Error_Type;
constraint Error_Type_c { error_mode dist {0:=25, 1:=75};
                          error_mode == 0 -> Error_Type == no_error;
                          solve error_mode before Error_Type;
                        }
3

In reply to dave_59:
thanks for your help Dave

4

Hi Guy,

Dave’s solution is good but the percentage of no_error packets will be greater than 25%:

  • 25% because error_mode will be 0 in 25% of the cases
    • an additional percentage because no_error will also appear when error_mode is 1

The complete solution is:


  rand bit error_mode;
  rand Error_t Error_Type;

  constraint Error_Type_c {
    solve error_mode before Error_Type;

    error_mode dist {0:=25, 1:=75};

    error_mode == 0 -> Error_Type == no_error;
    error_mode == 1 -> Error_Type != no_error;
  }

Best regards,
Daniel.

5

In reply to ciupitudan:

oh, right.
Thanks for pointing this issue for me Daniel :)
10x,
Guy

6

You can also write dist constraints on expressions, which will make the code shorter:



constraint error_distribution { 
  Error_Type == No_error dist {
    0 := 25,
    1 := 75
  };
7

In reply to Tudor Timi:

very elegant : )

thanks!