RE: [sv-cc] ref obj: more clarifications and issues

Francoise,
 
My first instinct is to model these portions of ref parent objects as
ref.
The main reason is that if we model them as normal variables, then it
would
be cumbersome to determine if the selected object is a ref or not.
A vpi programmer would always have to inspect upwards towards a parent
object until it could be fully determined that there is no ref in the
upward
object chain.  (Imagine a complex object with nested structs, unions,
arrays,
and a select made to a deep child in there).
 
What relationships do you think would be missing if these were modeled
as ref?
 
Thanks,
Doug
 


________________________________

	From: owner-sv-cc@eda.org [mailto:owner-sv-cc@eda.org] On Behalf
Of Francoise Martinolle
	Sent: Friday, April 08, 2005 5:54 PM
	To: sv-cc@eda.org
	Subject: [sv-cc] ref obj: more clarifications and issues
	
	
	I uploaded an update for the ref obj diagram, however I still
think that there are some 
	clarifications or issues with the access to ref obj.
	The access depicted by this diagram seems to only support ref
obj which represent the entire net/variable.
	However we could have an expression which is a bit select of a
net, a member select of a variable and the variable
	or net are passed by reference.
	 
	Consider the following example:
	ex:
	typedef struct { logic [1:0] m1; real m2 [2:0];} struct_t;
	 
	module m (ref struct_t v);
	 
	 initial begin
	     v.m1 = 2'b0;      ??
	     v.m1[1:0] = 2'b0;    ??
	     v.m1[0] = 1'b0;       ??
	     v.m2 = '{0.0. 1.0, 2.0};    ??
	     v.m2[2] = 3.0;     ??
	 end
	endmodule
	 
	v is a ref obj but what is v.m1? 
	If v was not passed by reference, v.m1 would be a logic var.
	But because v is passed by reference and v is a ref obj, does it
make it a ref obj?
	 
	Same question for v.m2. v.m2 would be an array var if v was not
passed by reference.
	 
	If v.m2 is a ref obj, what is its name and vpiActual returns?
	 
	I am also wondering what does the vpiParent relationship does?
Is it used for the purpose of walking from
	a sub ref obj to its parent ref obj (for instance from a var
select ref obj to the array 
	var ref obj like in the case of v.m2[2]?)
	 
	If we model all these uses as ref obj, I think that we are
missing a few relationships and properties to 
	be able to distinguish between the expressions in the example. 
	If we don't, is it okay to go from var select handle
representing v.m2[2] to a parent ref obj representing v?
	 
	Perhaps we can discuss these issues on Monday.
	 
	 
	Francoise
	       '