iverilog/docs/virtual-interface.md

Virtual interfaces (Tier A #3)

Status: partial — enough for basic UVM-agent style connectivity.

Supported in this slice

interface bus_if;
  logic clk;
  logic [7:0] data;
endinterface

class driver;
  virtual interface bus_if vif;          // class property
  function new(virtual interface bus_if i); // TF argument
    vif = i;                             // assign interface instance
  endfunction
  task drive(logic [7:0] d);
    @(posedge vif.clk);                  // edge wait via VI
    vif.data = d;                        // member write
  endtask
endclass

module top;
  bus_if bif();
  driver drv;
  initial begin
    drv = new(bif);
    // ...
  end
endmodule

Also: member reads (v = vif.data) and anyedge / negedge waits on VI members.

Syntax note: the type must be written as virtual interface <name>. Bare virtual bus_if is deferred (parser conflicts with virtual class / virtual function).

Encoding

Layer	Role
Parse	K_virtual_interface + virtual_interface_type_t (class props / TF ports)
Netlist	netvif_t (IVL_VT_CLASS so object load/store reuse works)
Elab	$ivl_vif_new / $ivl_vif_get / $ivl_vif_wait; VI member lvals
Runtime	vvp_vif + %new/vif, %vif/load/vec4, %vif/store/vec4, %vif/wait

A virtual interface is a handle to an interface instance: member access and waits go through the bound signals.

Example

examples/virtual_interface/vif_basic.sv — prints PASSED.

./install/bin/iverilog -g2012 -o /tmp/vif_basic.vvp examples/virtual_interface/vif_basic.sv
./install/bin/vvp /tmp/vif_basic.vvp

Deferred (do not claim)

• Bare virtual bus_if (without the interface keyword)
• Virtual interface arrays
• Modport-qualified virtual interfaces (type enforcement)
• Clocking blocks on VI (Tier A #4)
• Parameterized interfaces

See also STATUS.md and ROADMAP.md.