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//// fifoRTL.v                                                    ////

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//// This file is part of the usbhostslave opencores effort.

//// <http://www.opencores.org/cores//>                           ////

////                                                              ////

//// Module Description:                                          ////

////  parameterized fifo. fifo depth is restricted to 2^ADDR_WIDTH

////  No protection against over runs and under runs.

////  User must check full and empty flags before accessing fifo

//// 

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//// To Do:                                                       ////

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//// Author(s):                                                   ////

//// - Steve Fielding, sfielding@base2designs.com                 ////

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//// Copyright (C) 2004 Steve Fielding 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>                   ////

////                                                              ////

//////////////////////////////////////////////////////////////////////

//

// $Id: fifoRTL.v,v 1.1.1.1 2004-10-11 04:00:51 sfielding Exp $

//

// CVS Revision History

//

// $Log: not supported by cvs2svn $

//

`timescale 1ns / 1ps

module fifoRTL(clk, rst, dataIn, dataOut, fifoWEn, fifoREn, fifoFull, fifoEmpty, forceEmpty, numElementsInFifo);

//FIFO_DEPTH = ADDR_WIDTH^2. Min = 2, Max = 66536

  parameter FIFO_WIDTH = 8;

        parameter FIFO_DEPTH = 64;

  parameter ADDR_WIDTH = 6;

input clk;

input rst;

input [FIFO_WIDTH-1:0] dataIn;

output [FIFO_WIDTH-1:0] dataOut;

input fifoWEn;

input fifoREn;

output fifoFull;

output fifoEmpty;

input forceEmpty;

output [15:0]numElementsInFifo; //note that this implies a max fifo depth of 65536

wire clk;

wire rst;

wire [FIFO_WIDTH-1:0] dataIn;

reg [FIFO_WIDTH-1:0] dataOut;

wire fifoWEn;

wire fifoREn;

reg fifoFull;

reg fifoEmpty;

wire forceEmpty;

reg  [15:0]numElementsInFifo;

// local registers

reg  [ADDR_WIDTH-1:0]bufferInIndex;

reg  [ADDR_WIDTH-1:0]bufferOutIndex;

reg  [ADDR_WIDTH:0]bufferCnt;

reg  fifoREnDelayed;

wire [FIFO_WIDTH-1:0] dataFromMem;

always @(posedge clk)

begin

  if (rst == 1'b1 || forceEmpty == 1'b1)

  begin

    bufferCnt <= 0;

    fifoFull <= 1'b0;

    fifoEmpty <= 1'b1;

                bufferInIndex <= 0;

                bufferOutIndex <= 0;

    fifoREnDelayed <= 1'b0;

        end

    else

    begin

      if (fifoREn == 1'b1 && fifoREnDelayed == 1'b0) begin

        dataOut <= dataFromMem;

      end

      fifoREnDelayed <= fifoREn;

      if (fifoWEn == 1'b1 && fifoREn == 1'b0) begin

        bufferCnt <= bufferCnt + 1;

        bufferInIndex <= bufferInIndex + 1;

      end

      else if (fifoWEn == 1'b0 && fifoREn == 1'b1 && fifoREnDelayed == 1'b0) begin

        bufferCnt <= bufferCnt - 1;

        bufferOutIndex <= bufferOutIndex + 1;

      end

      else if (fifoWEn == 1'b1 && fifoREn == 1'b1 && fifoREnDelayed == 1'b0) begin

        bufferOutIndex <= bufferOutIndex + 1;

        bufferInIndex <= bufferInIndex + 1;

      end

      if (bufferCnt[ADDR_WIDTH] == 1'b1)

        fifoFull <= 1'b1;

      else

        fifoFull <= 1'b0;

      if (|bufferCnt == 1'b0)

        fifoEmpty <= 1'b1;

      else

        fifoEmpty <= 1'b0;

    end

end

//pad bufferCnt with leading zeroes

always @(bufferCnt) begin

  numElementsInFifo <= { {16-ADDR_WIDTH+1{1'b0}}, bufferCnt };

end

fifoMem #(FIFO_WIDTH, FIFO_DEPTH, ADDR_WIDTH)  u_fifoMem (

        .addrIn(bufferInIndex),

        .addrOut(bufferOutIndex),

        .clk(clk),

        .dataIn(dataIn),

        .writeEn(fifoWEn),

        .readEn(fifoREn),

        .dataOut(dataFromMem));

endmodule