Type-checking SystemVerilog interfaces using a class signature

As I wrote here,

Unlike class specializations, interface specializations cannot be used in a module port declaration. For example, the following is disallowed

module m #(parameter N) (IFC#(N) ifc, ...);

Steven Sharp followed up here that perhaps it was an oversight instead of a decision. Either way, it is still disallowed. He discusses some of the problems this causes for separate compilation. Happily, it is possible to get the effect of at least type checking SystemVerilog interfaces by combining class specializations (8.25) and interface-based typedefs (6.18) using a couple macros.

`define SIGNATURE_DEFINE(Params) \
   typedef SIGNATURE Params \%SIGNATURE ;

`define SIGNATURE_CHECK(Params, Port) \
  if (1) begin \
    typedef SIGNATURE Params Expected; \
    typedef Port.\%SIGNATURE Actual; \
    if (type(Expected) != type(Actual)) begin \
      $fatal("Mismatch"); \
    end \

Here’s a simple example

virtual class SIGNATURE#(int N, type T);

interface IFC#(int N, type T);
  T a[N], z[N];
  modport mp (input a, output z);

module top;
  IFC#(8,int) ifc_inst();
  test#(32,byte) test_inst(ifc_inst.mp);

module test#(int N, type T)(IFC.mp ifc_mp);
  `SIGNATURE_CHECK(/*IFC*/#(N,T), ifc_mp);
  // ...
Copyright © 2016 Brad Pierce

1 Comment

  1. Thanks Brad, that’s intriguing, a coding pattern that could be useful elsewhere too. Unfortunately it’s not very useful just now, as vendor support for the type() operator is – how shall we say – patchy.

    Could you, as a compiler guy, comment on whether the creation of large numbers of virtual class typedef specializations could be a significant overhead for elaboration?


Tell me (anonymous OK)

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s