How to dynamically Constrain range of coverage item in specman?

Question

Signal x is a one hot signal of bits 'n' I would like to cover only one hot values of the signal and not interested in other values.

Ex: if a signal x is of 3 bits then I would like does x is reaching below values are not.

x == 3'b001
x == 3'b010
x == 3'b100

I tried below to achieve goal.

struct ABC {
 x :uint(bits:n);
 event pqrs;
 cover pqrs is {
   item x using ranges={
                         range([1]);
                         range([2]);
                         range([4]);
                       };
 };

But above code is not elegant since 'n' `define value which can be varied based on environment. Please help me how to write coverage for above case.

Thanking all in advance for your help. Regards, Srikanth

Answer 1

you can write yourself a define-as-computed macro that creates the covergroup. Note that the macro must expand to the full syntactic element, you cannot just create a macro that creates the range expressions. (I have such a macro but cannot disclose it).

Thorsten.

Answer 2

you cam write a simple 'define as computed' macro to do so. i have written a short example below.

the macro should look like this :

 define <RANGE1'struct_member> "COVER_ITEM_WITH_DEFAULT_RANGES <struct_member>" as computed { 

var x:uint(bits:NBITS) = 1;
var str := append( "cover covT_e is also {",
  "item ", <1>," using ranges = {");
while(x!=0){
    str =append(str,"range([",x,"]);");
    x=x<<1;
};
  str=append(str,        "};",
                  "}"
                );
return str;
};

and the you can use that in your code like so :

<'
define NBITS 4;
import cover0;

extend sys {

 field1 : uint(bits:NBITS);
event covT_e;

cover covT_e is empty;          

COVER_ITEM_WITH_DEFAULT_RANGES field1;

run() is also {
    for i from 1 to 20 {
        gen field1;
          emit covT_e;
        print field1;
    }; // for i from 1 to...
}; // run() is also


finalize() is also{
    specman("show cover");
};
}; // extend sys
'>

hope this helps!