Question

The specify block is used to describe various paths across a module and perform timing checks to ensure that events occurring at the module inputs satisfy the timing constraints of the device described by the module. The module paths are from module input ports to output ports and the timing checks are relative to the module inputs. The specify block refers to these ports as terminal descriptor. Module inout ports can function as either an input or output terminal. When one of the port instances is an interface, each signal in the interface becomes an available terminal, with the default direction as defined for an interface, or as restricted by a modport. A ref port cannot be used as a terminal in a specify block.

The following shows an example of using interfaces together with a specify block:

interface itf;
    logic c,q,d;
    modport flop (input c,d, output q);
endinterface

module dtype (itf.flop ch);
    always_ff @(posedge ch.c) ch.q <= ch.d;
    specify
        ( posedge ch.c => (ch.q+:ch.d)) = (5,6);
        $setup( ch.d, posedge ch.c, 1 );
    endspecify
endmodule