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//////////////////////////////////////////////////////////////////////
//// 								  ////
//// divide for 8051 Core 				  	  ////
//// 								  ////
//// This file is part of the 8051 cores project 		  ////
//// http://www.opencores.org/cores/8051/ 			  ////
//// 								  ////
//// Description 						  ////
//// Two cycle implementation of division used in alu.v	          ////
//// 								  ////
//// To Do: 							  ////
////  check if compiler does proper optimizations of the code     ////
//// 								  ////
//// Author(s): 						  ////
//// - Simon Teran, simont@opencores.org 			  ////
//// - Marko Mlinar, markom@opencores.org 			  ////
//// 								  ////
//////////////////////////////////////////////////////////////////////
//// 								  ////
//// Copyright (C) 2001 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 			  ////
//// 								  ////
//////////////////////////////////////////////////////////////////////
//
// ver: 1
//
// ver: 2 markom
// changed nonsynthesizable version to two cycle divison
 
// synopsys translate_off
`include "oc8051_timescale.v"
// synopsys translate_on
 
module oc8051_divide (clk, rst, enable, src1, src2, des1, des2, desOv);
//
// this module is part of alu
// clk          (in)
// rst          (in)
// enable       (in)  starts divison
// src1         (in)  first operand
// src2         (in)  second operand
// des1         (out) first result
// des2         (out) second result
// desOv        (out) Overflow output
//
 
input clk, rst, enable;
input [7:0] src1, src2;
output desOv;
output [7:0] des1, des2;
 
// wires
reg desOv;
wire div0, div1;
wire [7:0] rem1, rem2;
wire [15:0] cmp0, cmp1;
reg [7:0] div_out, rem_out;
wire [7:0] div;
 
// real registers
reg cycle;
reg [5:0] tmp_div;
reg [7:0] tmp_rem;
 
/* This logic is very redundant, but it should be optimized by
   synthesizer */
assign cmp1 = src2 << ({1'b0, cycle} * 3'h2 + 3'h1);
assign cmp0 = src2 << ({1'b0, cycle} * 3'h2 + 3'h0);
 
assign rem2 = cycle != 0 ? tmp_rem : src1;
assign div1 = cmp1 <= rem2;
assign rem1 = rem1 - (div1 ? cmp1[7:0] : 8'h0);
assign div0 = cmp0 <= rem1;
 
//
// in clock cycle 0 we first calculate two MSB bits, ...
// till finally in clock cycle 3 we calculate two LSB bits
always @(rem1 or div0 or cmp0 or tmp_div or src2)
begin
  if (src2 == 8'h0) begin
    desOv = 1'b1;
    div_out = 8'hx;
    rem_out = 8'hx;
  end else begin
    desOv = 1'b0;
    rem_out = rem1 - (div0 ? cmp0[7:0] : 8'h0);
    div_out = {div1, div0, tmp_div};
  end
end
 
//
// divider works in four clock cycles -- 0, 1, 2 and 3
always @(posedge clk or posedge rst)
begin
  if (rst) begin
    cycle <= #1 1'b0;
    tmp_div <= #1 6'h0;
    tmp_rem <= #1 8'h0;
  end else begin
    if (enable && !cycle) cycle <= #1 1'b1;
    else cycle <= #1 1'b0;
    tmp_div <= #1 div_out[7:2];
    tmp_rem <= #1 rem_out;
  end
end
 
//
// assign outputs
assign des1 = rem_out;
assign des2 = div_out;
 
endmodule