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`timescale 1ns / 1ps

// ============================================================================

//        __

//   \\__/ o\    (C) 2007-2017  Robert Finch, Waterloo

//    \  __ /    All rights reserved.

//     \/_//     robfinch<remove>@finitron.ca

//       ||

//

// PSGHarmonicSynthsizer.v

// Harmonic synthesizer

//

// This source file is free software: you can redistribute it and/or modify 

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

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

// (at your option) any later version.                                      

//                                                                          

// This source file is distributed in the hope that it will be useful,      

// but WITHOUT ANY WARRANTY; without even the implied warranty of           

// MERCHANTABILITY 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.  If not, see <http://www.gnu.org/licenses/>.    

//                                                                          

//=============================================================================

module PSGHarmonicSynthesizer(rst, clk, test, sync, freq, o);

parameter WID = 32;

input rst;

input clk;

input test;

input sync;

input [WID-1:0] freq;   // frequency control

output [WID-1:0] o;

reg [WID-1:0] acc;

always @(posedge clk)

if (rst)

    acc <= 0;

else begin

    if (~test) begin

        if (sync)

            acc <= 0;

        else

            acc <= acc + freq;

    end

    else

        acc <= 0;

end

assign o = acc;

endmodule