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//////////////////////////////////////////////////////////////////////
////                                                              ////
////  OR1200's Write-back Mux                                     ////
////                                                              ////
////  This file is part of the OpenRISC 1200 project              ////
////  http://www.opencores.org/cores/or1k/                        ////
////                                                              ////
////  Description                                                 ////
////  CPU's write-back stage of the pipeline                      ////
////                                                              ////
////  To Do:                                                      ////
////   - make it smaller and faster                               ////
////                                                              ////
////  Author(s):                                                  ////
////      - Damjan Lampret, lampret@opencores.org                 ////
////                                                              ////
//////////////////////////////////////////////////////////////////////
////                                                              ////
//// Copyright (C) 2000 Authors and OPENCORES.ORG                 ////
////                                                              ////
//// This source file may be used and distributed without         ////
//// restriction provided that this copyright statement is not    ////
//// removed from the file and that any derivative work contains  ////
//// the original copyright notice and the associated disclaimer. ////
////                                                              ////
//// 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 2.1 of the License, or (at your option) any   ////
//// later version.                                               ////
////                                                              ////
//// This source 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 Lesser General Public License for more ////
//// details.                                                     ////
////                                                              ////
//// You should have received a copy of the GNU Lesser General    ////
//// Public License along with this source; if not, download it   ////
//// from http://www.opencores.org/lgpl.shtml                     ////
////                                                              ////
//////////////////////////////////////////////////////////////////////
//
// CVS Revision History
//
// $Log: not supported by cvs2svn $
// Revision 1.1.1.1  2001/10/06 10:18:36  igorm
// no message
//
// Revision 1.2  2001/08/09 13:39:33  lampret
// Major clean-up.
//
// Revision 1.1  2001/07/20 00:46:23  lampret
// Development version of RTL. Libraries are missing.
//
//
 
// synopsys translate_off
`include "timescale.v"
// synopsys translate_on
`include "defines.v"
 
module wbmux(
	// Clock and reset
	clk, rst,
 
	// Internal i/f
	wb_freeze, rfwb_op,
	muxin_a, muxin_b, muxin_c, muxin_d,
	muxout, muxreg, muxreg_valid
);
 
parameter width = `OPERAND_WIDTH;
 
//
// I/O
//
 
//
// Clock and reset
//
input				clk;
input				rst;
 
//
// Internal i/f
//
input				wb_freeze;
input	[`RFWBOP_WIDTH-1:0]	rfwb_op;
input	[width-1:0]		muxin_a;
input	[width-1:0]		muxin_b;
input	[width-1:0]		muxin_c;
input	[width-1:0]		muxin_d;
output	[width-1:0]		muxout;
output	[width-1:0]		muxreg;
output				muxreg_valid;
 
//
// Internal wires and regs
//
reg	[width-1:0]		muxout;
reg	[width-1:0]		muxreg;
reg				muxreg_valid;
 
//
// Registered output from the write-back multiplexer
//
always @(posedge clk or posedge rst) begin
	if (rst) begin
		muxreg <= #1 32'd0;
		muxreg_valid <= #1 1'b0;
	end
	else if (!wb_freeze) begin
		muxreg <= #1 muxout;
		muxreg_valid <= #1 rfwb_op[0];
	end
end
 
//
// Write-back multiplexer
//
always @(muxin_a or muxin_b or muxin_c or muxin_d or rfwb_op) begin
	case(rfwb_op[`RFWBOP_WIDTH-1:1]) // synopsys full_case parallel_case infer_mux
		2'b00: muxout = muxin_a;
		2'b01: begin
			muxout = muxin_b;
`ifdef OR1200_VERBOSE
// synopsys translate_off
			$display("  WBMUX: muxin_b %h", muxin_b);
// synopsys translate_on
`endif
		end
		2'b10: begin
			muxout = muxin_c;
`ifdef OR1200_VERBOSE
// synopsys translate_off
			$display("  WBMUX: muxin_c %h", muxin_c);
// synopsys translate_on
`endif
		end
		2'b11: begin
			muxout = muxin_d + 4'h8;
`ifdef OR1200_VERBOSE
// synopsys translate_off
			$display("  WBMUX: muxin_d %h", muxin_d + 4'h8);
// synopsys translate_on
`endif
		end
	endcase
end
 
endmodule