Interface

SV Verification Directory

Interface

Interface in SystemVerilog is a construct that bundles all the signals together or group related to signals so that they can be shared among multiple modules in the verification environment. This simplifies the connection between modules, improves code readability, and reduces the likelihood of errors in complex designs.

Syntax

// create interface
interface interface_name;
   signals;
endinterface


// intantiate interface in a module
inteface_name inst_name;

Example Code

• Design

  module add (
    // outputs
    s,
    // inputs
    a, b );
  
    // outputs
    output [4:0] s;
  
    // inputs
    input [3:0] a, b;
  
    assign s = a + b;
  
  endmodule
  

• Testbench

  interface intf;
    logic [3:0] a;
    logic [3:0] b;
    logic [4:0] s;
  endinterface
  
  module test;
  
    intf i_intf();
  
    add DUT(.a(i_intf.a),
            .b(i_intf.b),
            .s(i_intf.s));
  
    initial begin
      $display("---------- ADDER ----------");
      repeat(10) begin
        i_intf.a = $random();
        i_intf.b = $random();
        #1;
        $display("a = %d, b = %d => s = %d", i_intf.a, i_intf.b, i_intf.s);
      end
    end
  endmodule
  

  Execute the code in EDA Playground

Advantages

1. Addition and deletion od signals are easy since all the signals are at one place.
2. The signals can be grouped and passed as a signal port rather than multiple port declaration.
3. Signals can be grouped based on direction (Modport) and timing information (Clocking Block).

Virtual Interface

• Both the interface and module are static, meaning they exist throughout the simulation and are straightforward to connect.
• Since both are static, connecting them is as simple as wiring them together.
• Unlike interfaces, classes are dynamic—they are instantiated only when needed.
• Interfaces, being static, cannot be directly used inside a class since the two follow different lifecycles.
• To access an interface from within a class, the virtual keyword must be used during instantiation.
• A virtual interface provides a handle to the static interface, allowing it to be used within a class-based environment.
• One advantage of a virtual interface is that it can be assigned dynamically at runtime, providing flexibility.
• A virtual interface must be initialized (assigned to a valid interface instance) before it can be accessed or driven. Failure to do so will result in errors during simulation.