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////////////////////////////////////////////////////////////////////////////////

//

// Filename:    bigsub.v

//

// Project:     OpenArty, an entirely open SoC based upon the Arty platform

//

// Purpose:     

//

// Creator:     Dan Gisselquist, Ph.D.

//              Gisselquist Technology, LLC

//

////////////////////////////////////////////////////////////////////////////////

//

// Copyright (C) 2016, Gisselquist Technology, LLC

//

// This program is free software (firmware): you can redistribute it and/or

// modify it under the terms of  the GNU General Public License as published

// by the Free Software Foundation, either version 3 of the License, or (at

// your option) any later version.

//

// This program is distributed in the hope that it will be useful, but WITHOUT

// ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY or

// FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

// for more details.

//

// You should have received a copy of the GNU General Public License along

// with this program.  (It's in the $(ROOT)/doc directory, run make with no

// target there if the PDF file isn't present.)  If not, see

// <http://www.gnu.org/licenses/> for a copy.

//

// License:     GPL, v3, as defined and found on www.gnu.org,

//              http://www.gnu.org/licenses/gpl.html

//

//

////////////////////////////////////////////////////////////////////////////////

//

//

module  bigsub(i_clk, i_sync, i_a, i_b, o_r, o_sync);

        input                   i_clk, i_sync;

        input           [63:0]   i_a, i_b;

        output  reg     [63:0]   o_r;

        output  reg     o_sync;

        reg             r_sync, r_pps;

        reg     [31:0]   r_hi_a, r_hi_b, r_low;

        initial r_sync = 1'b0;

        always @(posedge i_clk)

                r_sync <= i_sync;

        always @(posedge i_clk)

                { r_pps, r_low } <= i_a[31:0] + ({1'b1,~i_b[31:0]}) + 1'b1;

        always @(posedge i_clk)

                r_hi_a <= i_a[63:32];

        always @(posedge i_clk)

                r_hi_b <= ~i_b[63:32];

        initial o_sync = 1'b0;

        always @(posedge i_clk)

                o_sync <= r_sync;

        always @(posedge i_clk)

                o_r[31:0] <= r_low;

        always @(posedge i_clk)

                o_r[63:32] <= r_hi_a + r_hi_b + { 31'h00, r_pps };

endmodule