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/*

 Asynchronous SDM NoC

 (C)2011 Wei Song

 Advanced Processor Technologies Group

 Computer Science, the Univ. of Manchester, UK

 Authors:

 Wei Song     wsong83@gmail.com

 License: LGPL 3.0 or later

 XY address decoder, 1-of-4 code

 * Assuming the output will be capture for long time

 * The withdrawal of inputs are not guarded

 History:

 14/07/2010  Initial version. <wsong83@gmail.com>

*/

module addr_dec(/*AUTOARG*/

   // Outputs

   dec,

   // Inputs

   locx, locy, tarx, tary

   );

   input [7:0] locx, locy;       // the local addresses

   input [7:0] tarx, tary;       // the target addresses in the incoming frame

   output [4:0] dec;             // the decoded routing request

   wire [3:0][2:0] cmp;           // compare results

   comp4 X0 (.a(tarx[3:0]), .b(locx[3:0]), .q(dec[0]));

   comp4 X1 (.a(tarx[7:4]), .b(locx[7:4]), .q(dec[1]));

   comp4 Y0 (.a(tary[3:0]), .b(locy[3:0]), .q(dec[2]));

   comp4 Y1 (.a(tary[7:4]), .b(locy[7:4]), .q(dec[3]));

   assign dec[0] = dec[1][1] | (dec[1][2]&dec[0][1]); // south, tarx < locx

   assign dec[1] = dec[1][2]&dec[0][2]&(dec[3][0]|(dec[3][2]&dec[2][0])); // west, tary > locy

   assign dec[2] = dec[1][0] | (dec[1][2]&dec[0][0]); // north, tarx < locx

   assign dec[3] = dec[1][2]&dec[0][2]&(dec[3][1]|(dec[3][2]&dec[2][1])); // west, tary < locy

   assign dec[4] = dec[3][2]&dec[2][2]&dec[1][2]&dec[0][2];

endmodule // addr_dec