//------------------------------------------------------------------------------
//
// tb_lowlevel_subtractor32.v
// -----------------------------------------------------------------------------
// Testbench for 32-bit subtractor.
//
// Authors: Pavel Shatov
//
// Copyright (c) 2015-2016, NORDUnet A/S
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// - Redistributions of source code must retain the above copyright notice,
//   this list of conditions and the following disclaimer.
//
// - Redistributions in binary form must reproduce the above copyright notice,
//   this list of conditions and the following disclaimer in the documentation
//   and/or other materials provided with the distribution.
//
// - Neither the name of the NORDUnet nor the names of its contributors may be
//   used to endorse or promote products derived from this software without
//   specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
// POSSIBILITY OF SUCH DAMAGE.
//
//------------------------------------------------------------------------------


//------------------------------------------------------------------------------
`timescale 1ns / 1ps
//------------------------------------------------------------------------------

module tb_lowlevel_subtractor32;

   //
   // Inputs
   //
   reg				clk;
   reg [31: 0] 			a;
   reg [31: 0] 			b;
   reg				b_in;

   //
   // Outputs
   //
   wire [31: 0] 		d;
   wire				b_out;

   //
   // Test Vectors {a, b, b_in}
   //
   wire [64: 0] 		vec_0		= {32'h00000000, 32'h00000000, 1'b0};	// all zeroes, no borrow
   wire [64: 0] 		vec_1		= {32'h00000000, 32'h00000000, 1'b1};	// all zeroes with borrow
   wire [64: 0] 		vec_2		= {32'h00000000, 32'hFFFFFFFF, 1'b0};	// zeroes and ones, no borrow
   wire [64: 0] 		vec_3		= {32'h00000000, 32'hFFFFFFFF, 1'b1};	// zeroes and ones with borrow
   wire [64: 0] 		vec_4		= {32'hFFFFFFFF, 32'h00000000, 1'b0};	// ones and zeroes, no borrow
   wire [64: 0] 		vec_5		= {32'hFFFFFFFF, 32'h00000000, 1'b1};	// ones and zeroes with borrow
   wire [64: 0] 		vec_6		= {32'hFFFFFFFF, 32'hFFFFFFFF, 1'b0};	// all ones, no borrow
   wire [64: 0] 		vec_7		= {32'hFFFFFFFF, 32'hFFFFFFFF, 1'b1};	// all ones with borrow

   wire [64: 0] 		vec_8		= {32'hd898c296, 32'h37bf51f5, 1'b0};	// random values, no borrow
   wire [64: 0] 		vec_9		= {32'hf4a13945, 32'hcbb64068, 1'b0};	// random values, no borrow
   wire [64: 0] 		vec_10	= {32'h2deb33a0, 32'h6b315ece, 1'b0};	// random values, no borrow
   wire [64: 0] 		vec_11	= {32'h77037d81, 32'h2bce3357, 1'b0};	// random values, no borrow
   wire [64: 0] 		vec_12	= {32'h63a440f2, 32'h7c0f9e16, 1'b1};	// random values with borrow
   wire [64: 0] 		vec_13	= {32'hf8bce6e5, 32'h8ee7eb4a, 1'b1};	// random values with borrow
   wire [64: 0] 		vec_14	= {32'he12c4247, 32'hfe1a7f9b, 1'b1};	// random values with borrow
   wire [64: 0] 		vec_15	= {32'h6b17d1f2, 32'h4fe342e2, 1'b1};	// random values with borrow


   //
   // UUT
   //
   subtractor32_wrapper uut
     (
      .clk		(clk),
      .a		(a),
      .b		(b),
      .d		(d),
      .b_in		(b_in),
      .b_out		(b_out)
      );


   //
   // Testbench Routine
   //
   reg 			ok = 1;
   initial begin
      //
      clk = 0;
      //
      #100;
      //
      test_subtractor32(vec_0);
      test_subtractor32(vec_1);
      test_subtractor32(vec_2);
      test_subtractor32(vec_3);
      test_subtractor32(vec_4);
      test_subtractor32(vec_5);
      test_subtractor32(vec_6);
      test_subtractor32(vec_7);
      //
      test_subtractor32(vec_8);
      test_subtractor32(vec_9);
      test_subtractor32(vec_10);
      test_subtractor32(vec_11);
      test_subtractor32(vec_12);
      test_subtractor32(vec_13);
      test_subtractor32(vec_14);
      test_subtractor32(vec_15);
      //
      if (ok)	$display("tb_lowlevel_subtractor32: SUCCESS");
      else	$display("tb_lowlevel_subtractor32: FAILURE");
      //
      $finish;
      //
   end


   //
   // Test Routine
   //
   reg	[31: 0]	dd;		// reference value of difference
   reg 		bb;		// reference value of borrow
   reg 		dd_ok;	// result matches reference value

   task test_subtractor32;

      input	[64: 0] vec;

      begin

	 /* break down test vector */
	 a		= vec[64:33];
	 b		= vec[32: 1];
	 b_in	= vec[ 0: 0];

	 /* calculate reference values */
	 {bb, dd} = {1'b0, a} - {1'b0, b} - {32'd0, b_in};

	 /* send one clock tick */
	 #10 clk = 1;
	 #10 clk = 0;

	 /* check outputs */
	 dd_ok = (d == dd) && (b_out == bb);

	 /* display results */
	 $display("test_subtractor32(): 0x%08X - (0x%08X + %01d) = {%01d, 0x%08X} [%0s]", a, b, b_in, b_out, d, dd_ok ? "OK" : "ERROR");

	 /* update global flag */
	 ok = ok && dd_ok;

      end

   endtask

endmodule

//------------------------------------------------------------------------------
// End-of-File
//------------------------------------------------------------------------------