Re: [sv-ec] implicit sensitivity list and class dynamic members

Mark,

always_comb addresses the class method side directly in the text I
quoted so I don't think virtual comes into play -- you don't impact
the sensitivity list with a virtual method call either.

I view the "write rule" for always_comb as being tied to the
sensitivity lists -- if we ignore methods and class objects for
sensitivity, I think they should also be ignored for the
"write rule".

Gord.



Mark Hartoog wrote:
> I agree with Gord's interpretation that class objects, class methods and class properties do not add to the sensitivity list of always_comb or @(*).
> 
> If Daniel's question is should the LRM be changed to allow this, there are a number of issues to consider.
> 
> Always_comb sensitivity lists include sensitivities from functions called from the always_comb. Since class methods can be virtual, there is no way to do this for virtual class methods.
> 
> Always_comb also says it is an error for multiple always_comb to write to the same variable. The aliasing problem with class handles makes it very difficult to do this check for class fields.
> 
> 
> -----Original Message-----
> From: owner-sv-ec@eda.org [mailto:owner-sv-ec@eda.org] On Behalf Of Gordon Vreugdenhil
> Sent: Friday, July 24, 2009 6:49 AM
> To: Daniel Mlynek
> Cc: sv-ec@eda.org
> Subject: Re: [sv-ec] implicit sensitivity list and class dynamic members
> 
> Daniel,
> 
> 9.2.2.2.1 explicitly deals with always_comb:
>     References to class objects and method calls of class objects do
>     not add anything to the sensitivity list of an always_comb.
> 
> 9.2.2.2.2 (on @(*)) is less clear although it claims that
>     The SystemVerilog always_comb procedure differs from
>     always @* (see 9.4.2.2) in the following ways:
>        ...
> 
> Whether @(*) is sensitive to class refs was never explicitly
> addressed in the LRM, but it would be reasonable to interpret
> the lack of comment about classes in 9.2.2.2.2 to imply that
> @(*) should be sensitized to class references either.
> 
> Gord.
> 
> Daniel Mlynek wrote:
>> I've a question related to implicit sensitivity list (@*, always_comb).
>> This feature was assumed to help users in design code - for
>> combinatorial blocks. But in blocks under @* or always_comb also
>> references to dynamic class members can be used - as in below code.
>> Should such references be added to implicit sensitivity list>
>>
>>     class class0;
>>      int x;
>>     endclass
>>
>>     module top_006;
>>      class0 c0 = new;
>>      class0 c1 = new;
>>
>>      initial begin
>>         #10 c0.x = 1;
>>         #10 c0.x = 0;
>>         #10 c0.x = 1;
>>         #10 c0 = c1;
>>      end
>>      always@* $display($time, c0.x);        //should this be sensitive
>>     to c0.x?
>>     endmodule
>>
>> DANiel
>>
>> --
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> --
> --------------------------------------------------------------------
> Gordon Vreugdenhil                                503-685-0808
> Model Technology (Mentor Graphics)                gordonv@model.com
> 
> 
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Gordon Vreugdenhil                                503-685-0808
Model Technology (Mentor Graphics)                gordonv@model.com


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