Systemverilog interface definition - lint error message

Question

I'm using Systemverilog interfaces to enable the implementation of generic functions. The interface is defined in one file as follows:

interface interface_onehot_to_binary
# (parameter WIDTH_ONEHOT=16)
(); // Empty port list
localparam WIDTH_BINARY = $clog2 (WIDTH_ONEHOT) ;
 function logic [WIDTH_BINARY-1:0] onehot_to_binary
 (logic [WIDTH_ONEHOT-1: 0] onehot);
 automatic logic [WIDTH_BINARY-1:0] binary=0;
 foreach (onehot[index])
 begin
 if (onehot[index]==1'b1) begin
 binary=binary|index;
 end
 end
 return binary;
 endfunction
endinterface

And then instantiated in another file as follows:

interface_onehot_to_binary
#(.WIDTH_ONEHOT(256))
inst_interface_onehot_to_binary
(); // Empty port list

The simulation and synthesis tools that I use digest this code without issues. But the SpyGlass linter fails with the following error message: interface 'interface_onehot_to_binary' declaration does not have a modport definition. The error points to the first file - where the interface is defined. What's wrong with my code? How can it be solved?

• dave_59: This seems like a strange use of an interface. Why not put your function in a package?
• shaiko: Because I want the function to be generic. To my understanding, if I store the function in a package I'll have to statically declare WIDTH_ONEHOT using a localparam in that package. An interface on the other hand allows me to pass the width using a parameter.
• dave_59: You can make the function a static method of a parameterized class. (and synthesizable).
• shaiko: I would love to learn that. Can you please post an example of my function modified to the form that you mentioned ?

Answer 1

class class_onehot_to_binary
# (parameter WIDTH_ONEHOT=16);
localparam WIDTH_BINARY = $clog2 (WIDTH_ONEHOT) ;
 static function logic [WIDTH_BINARY-1:0] onehot_to_binary
 (logic [WIDTH_ONEHOT-1: 0] onehot);
 logic [WIDTH_BINARY-1:0] binary=0;
 foreach (onehot[index])
 begin
 if (onehot[index]==1'b1) begin
 binary=binary|index;
 end
 end
 return binary;
 endfunction
endclass

Note that even though onehot_to_binary has a static class qualifier, the function has an automatic lifetime.

You would call this using class_onehot_to_binary#(32)::onehot_to_binary(value)

• shaiko: Thanks! If the class is declared in a package - shouldn't we call it as some_pkg::class_onehot_to_binary#(32)::onehot_to_binary(value) ?