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

////                                                              ////

//// fifoRTL.v                                                    ////

////                                                              ////

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

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

////                                                              ////

//// Module Description:                                          ////

////  parameterized dual clock domain fifo. 

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

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

//// 

////                                                              ////

//// To Do:                                                       ////

//// 

////                                                              ////

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

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

////                                                              ////

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

////                                                              ////

//// 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>                   ////

////                                                              ////

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

//

`timescale 1ns / 1ps

module fifoRTL(wrClk, rdClk, rstSyncToWrClk, rstSyncToRdClk, dataIn,

  dataOut, fifoWEn, fifoREn, fifoFull, fifoEmpty,

  forceEmptySyncToWrClk, forceEmptySyncToRdClk, numElementsInFifo);

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

  parameter FIFO_WIDTH = 8;

  parameter FIFO_DEPTH = 64;

  parameter ADDR_WIDTH = 6;

// Two clock domains within this module

// These ports are within 'wrClk' domain

input wrClk;

input rstSyncToWrClk;

input [FIFO_WIDTH-1:0] dataIn;

input fifoWEn;

input forceEmptySyncToWrClk;

output fifoFull;

// These ports are within 'rdClk' domain

input rdClk;

input rstSyncToRdClk;

output [FIFO_WIDTH-1:0] dataOut;

input fifoREn;

input forceEmptySyncToRdClk;

output fifoEmpty;

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

wire wrClk;

wire rdClk;

wire rstSyncToWrClk;

wire rstSyncToRdClk;

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:0]bufferInIndex;

reg  [ADDR_WIDTH:0]bufferInIndexSyncToRdClk;

reg  [ADDR_WIDTH:0]bufferOutIndex;

reg  [ADDR_WIDTH:0]bufferOutIndexSyncToWrClk;

reg  [ADDR_WIDTH-1:0]bufferInIndexToMem;

reg  [ADDR_WIDTH-1:0]bufferOutIndexToMem;

reg  [ADDR_WIDTH:0]bufferCnt;

reg  fifoREnDelayed;

wire [FIFO_WIDTH-1:0] dataFromMem;

always @(posedge wrClk)

begin

  bufferOutIndexSyncToWrClk <= bufferOutIndex;

  if (rstSyncToWrClk == 1'b1 || forceEmptySyncToWrClk == 1'b1)

  begin

    fifoFull <= 1'b0;

    bufferInIndex <= 0;

  end

    else

    begin

      if (fifoWEn == 1'b1) begin

        bufferInIndex <= bufferInIndex + 1'b1;

      end

      if ((bufferOutIndexSyncToWrClk[ADDR_WIDTH-1:0] == bufferInIndex[ADDR_WIDTH-1:0]) &&

          (bufferOutIndexSyncToWrClk[ADDR_WIDTH] != bufferInIndex[ADDR_WIDTH]) )

        fifoFull <= 1'b1;

      else

        fifoFull <= 1'b0;

    end

end

always @(bufferInIndexSyncToRdClk or bufferOutIndex)

  bufferCnt <= bufferInIndexSyncToRdClk - bufferOutIndex;

always @(posedge rdClk)

begin

  numElementsInFifo <= { {16-ADDR_WIDTH+1{1'b0}}, bufferCnt }; //pad bufferCnt with leading zeroes

  bufferInIndexSyncToRdClk <= bufferInIndex;

  if (rstSyncToRdClk == 1'b1 || forceEmptySyncToRdClk == 1'b1)

  begin

    fifoEmpty <= 1'b1;

    bufferOutIndex <= 0;

    fifoREnDelayed <= 1'b0;

  end

    else

    begin

      fifoREnDelayed <= fifoREn;

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

        dataOut <= dataFromMem;

        bufferOutIndex <= bufferOutIndex + 1'b1;

      end

      if (bufferInIndexSyncToRdClk == bufferOutIndex)

        fifoEmpty <= 1'b1;

      else

        fifoEmpty <= 1'b0;

    end

end

always @(bufferInIndex or bufferOutIndex) begin

  bufferInIndexToMem <= bufferInIndex[ADDR_WIDTH-1:0];

  bufferOutIndexToMem <= bufferOutIndex[ADDR_WIDTH-1:0];

end

dpMem_dc #(FIFO_WIDTH, FIFO_DEPTH, ADDR_WIDTH)  u_dpMem_dc (

  .addrIn(bufferInIndexToMem),

  .addrOut(bufferOutIndexToMem),

  .wrClk(wrClk),

  .rdClk(rdClk),

  .dataIn(dataIn),

  .writeEn(fifoWEn),

  .readEn(fifoREn),

  .dataOut(dataFromMem));

endmodule