RE: [sv-ac] 1728 mantis: "let" construct vs function

Mirek,

 

I agree with you. This has been my issue with let as well. We tried to
do this in Accellera, but ran out of time and never came back to it.
This construct needs to be generalized for use in expressions other than
just assertions.

 

Dave

 

 

________________________________

From: owner-sv-ac@server.eda.org [mailto:owner-sv-ac@server.eda.org] On
Behalf Of Mirek Forczek
Sent: Monday, April 07, 2008 7:34 AM
To: sv-ac@server.eda.org
Subject: [sv-ac] 1728 mantis: "let" construct vs function

 

Hi,

 

The 1728 mantis introduces 'let' construct: the motivation is given as:

 

"Including let expressions into packages (See Clause 25) is a natural
way to implement a well-structured customization for assertions."

 

there is an example also:

 

// in a package
let at_least_two(sig, rst = 1'b0) = rst || ($countones(sig) >= 2);


// in a design
reg [15:0] sig1; reg [3:0] sig2;
    always_comb begin
        q1: assert (at_least_two(sig1));
        q2: assert (at_least_two(~sig2));
    end

 

 

I'm wondering if the same could be achieved just with functions (?):

 

// in a package
function automatic bit at_least_two(sig, rst = 1'b0);

    return rst || ($countones(sig) >= 2);

endfunction


// in a design (no change at all vs 'let' version)
reg [15:0] sig1; reg [3:0] sig2;
    always_comb begin
        q1: assert (at_least_two(sig1));
        q2: assert (at_least_two(~sig2));
    end

 

 

Are there any other benefits in having 'let' construct over already
existing 'function' ?

 

If it is about unbounded argument types in 'let' construct, a
parametrized function and tasks shall be considered as an alternative.

They shall provide same flexibility as the "let" construct but they
would be an extension of an existing concept (function, task) instead of
a brand new one (let).

The parametrized function and tasks extension (functions and tasks with
#parameters - in particular: with type parameters) would be consistent
with already intorduced concpet of the parametrized classes - and their
methods in particular.

 

 

Regards,

Mirek

  


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