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

There may be contexts where certain argument types are not allowed, just
as immediate assertions will have restrictions on what could be used
inside a let.

 

________________________________

From: owner-sv-ac@server.eda.org [mailto:owner-sv-ac@server.eda.org] On
Behalf Of Bresticker, Shalom
Sent: Monday, April 07, 2008 7:56 AM
To: Mirek Forczek; sv-ac@server.eda.org
Subject: RE: [sv-ac] 1728 mantis: "let" construct vs function

 

There are several advantages to let over parameterized tasks and
functions (which have not been done yet because it is not trivial to do
so). Others can explain them better than I. One example, though, is that
let arguments can be sequences and properties. Another is their context
sensitiveness.

 

Shalom

	 

	
________________________________


	From: owner-sv-ac@server.eda.org
[mailto:owner-sv-ac@server.eda.org] On Behalf Of Mirek Forczek
	Sent: Monday, April 07, 2008 5:34 PM
	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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