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+//======================================================================
+//
+// rosc.v
+// ---------
+// Digital ring oscillator used as entropy source.
+//
+//
+// Author: Bernd Paysan
+// Copyright (c) 2014, Bernd Paysan
+// All rights reserved.
+// 
+// Redistribution and use in source and binary forms, with or 
+// without modification, are permitted provided that the following 
+// conditions are met: 
+// 
+// 1. Redistributions of source code must retain the above copyright 
+//    notice, this list of conditions and the following disclaimer. 
+// 
+// 2. 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. 
+// 
+// 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 OWNER 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.
+//
+//======================================================================
+
+module rosc(clk, nreset, in1, in2, dout);
+   parameter l=8;
+   input clk, nreset;
+   input [l-1:0] in1, in2;
+   output reg 	 dout;
+
+   wire 	 cin;
+   wire [l:0]  sum = in1 + in2 + cin;
+
+   assign cin = ~sum[l];
+
+   always @(posedge clk or negedge nreset)
+     if(!nreset)
+       dout <= 0;
+     else
+       dout <= sum[l];
+   
+endmodule // rosc
+
+//======================================================================
+// EOF rosc.v
+//======================================================================