I had expected all 3 of these calls to randomize to return values using the constraint. However, the first does not. Can anyone tell me why?
class thursday_seq extends junk_seq_seq; //which extends uvm_sequence
rand int count;
constraint c1 { count >= 2; count <= 9; }
function new(string name="thursday_seq");
super.new(name);
if (std::randomize(count)) begin
`uvm_info("",$psprintf(" cnt=%0d .....",count),UVM_LOW) end
else $finish;
if (randomize(count)) begin
`uvm_info("",$psprintf(" cnt=%0d .....",count),UVM_LOW) end
else $finish;
if (this.randomize()) begin
`uvm_info("",$psprintf(" cnt=%0d .....",count),UVM_LOW) end
else $finish;
$finish;
endfunction:new
UVM_INFO @ 0: reporter@ [] cnt=415747889 ..... UVM_INFO @ 0: reporter@ [] cnt=9 ..... UVM_INFO @ 0: reporter@ [] cnt=2 .....
It seems what is happening is that while std::randomize and randomize are calling the same method in the standard package, the standard version is oblivious to local constraints.
I see in 1800-2012.pdf (SV spec), sec. 18.5.2 "The randomize() method is virtual and therefore honors constraints of the object on which it was called, ..." (highlighting mine)
Later in the spec, there is reference to the 'scope of the randomize(' which confuses me a bit, if the constraints are always to be honored. (Although, I suppose in the first two cases above "of the object on which it was called" is not true, b/c I don't call it on the object, but on a property of the object.) Is that correct?
After doing a bunch more reading, I am going to continue with this post for feedback. Here is something more I learned.
This quote in section "18.12 Randomization of scope variables—std::randomize()" I think explains it all for me.
I'm a bit unsure, but I think the answer to my question is this.
"without the need to define a class" and "in the current scope", from above, imply that std::randomize performs only on the scope that is passed to it. i.e. if I pass it a class object, then it knows of that object's constraints. If I pass it a data-member of a class, then the scope that data-member exists in is not seen (i.e. any constraints which are in the scope above that data-member are not seen). Though they could be replicated as inline constraints.).
The local randomize knows of all the constraints in the object from which it is called.
Do I understand this correctly? I think I just walked myself through understanding this. Comments welcome.
thx,
note: using Cadence's IUS12.1-s004