/********************************************************************** * Code snippet showing declaration order dependency with $unit space * * Author: Stuart Sutherland * * (c) Copyright 2003, Sutherland HDL, Inc. *** ALL RIGHTS RESERVED *** * www.sutherland-hdl.com * * Used with permission in the book, "SystemVerilog for Design" *  By Stuart Sutherland, Simon Davidmann, and Peter Flake. *  Book copyright: 2003, Kluwer Academic Publishers, Norwell, MA, USA *  www.wkap.il, ISBN: 0-4020-7530-8 * * Revision History: *   1.00 15 Dec 2003 -- original code, as included in book *   1.01 10 Jul 2004 -- cleaned up comments, added expected results *                       to output messages * * Caveat: Expected results displayed for this code example are based * on an interpretation of the SystemVerilog 3.1 standard by the code * author or authors.  At the time of writing, official SystemVerilog * validation suites were not available to validate the example. * * RIGHT TO USE: This code example, or any portion thereof, may be * used and distributed without restriction, provided that this entire * comment block is included with the example. * * DISCLAIMER: THIS CODE EXAMPLE IS PROVIDED "AS IS" WITHOUT WARRANTY * OF ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING, BUT NOT LIMITED * TO WARRANTIES OF MERCHANTABILITY, FITNESS OR CORRECTNESS. IN NO * EVENT SHALL THE AUTHOR OR AUTHORS BE LIABLE FOR ANY DAMAGES, * INCLUDING INCIDENTAL OR CONSEQUENTIAL DAMAGES, ARISING OUT OF THE * USE OF THIS CODE. *********************************************************************/module parity_check (input wire [63:0] data );  assign parity = ^data; // parity is anendmodule                // implicit local netreg parity;  // $unit declaration is not used             // by module parity_checkmodule test;  reg [63:0] data;  parity_check dut (data);  initial    begin      parity = 'x; // set $unit parity      data = 32;    // should change parity      #1 $display("\n $unit parity = %b (expect x)", parity);         $display("\n dut.parity = %b (expect 1)\n", dut.parity);    endendmodule