Subversion Repositories openrisc

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

////                                                              ////

//// RxfifoBI.v                                                   ////

////                                                              ////

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

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

////                                                              ////

//// Module Description:                                          ////

//// 

////                                                              ////

//// 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>                   ////

////                                                              ////

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

//

`include "timescale.v"

`include "usbhostslave_wishbonebus_h.v"

module RxfifoBI (

  address,

  writeEn,

  strobe_i,

  busClk,

  usbClk,

  rstSyncToBusClk,

  fifoSelect,

  fifoDataIn,

  busDataIn,

  busDataOut,

  fifoREn,

  forceEmptySyncToUsbClk,

  forceEmptySyncToBusClk,

  numElementsInFifo

  );

input [2:0] address;

input writeEn;

input strobe_i;

input busClk;

input usbClk;

input rstSyncToBusClk;

input [7:0] fifoDataIn;

input [7:0] busDataIn;

output [7:0] busDataOut;

output fifoREn;

output forceEmptySyncToUsbClk;

output forceEmptySyncToBusClk;

input [15:0] numElementsInFifo;

input fifoSelect;

wire [2:0] address;

wire writeEn;

wire strobe_i;

wire busClk;

wire usbClk;

wire rstSyncToBusClk;

wire [7:0] fifoDataIn;

wire [7:0] busDataIn;

reg [7:0] busDataOut;

reg fifoREn;

wire forceEmptySyncToUsbClk;

wire forceEmptySyncToBusClk;

wire [15:0] numElementsInFifo;

wire fifoSelect;

reg forceEmptyReg;

reg forceEmpty;

reg forceEmptyToggle;

reg [2:0] forceEmptyToggleSyncToUsbClk;

//sync write

always @(posedge busClk)

begin

  if (writeEn == 1'b1 && fifoSelect == 1'b1 &&

    address == `FIFO_CONTROL_REG && strobe_i == 1'b1 && busDataIn[0] == 1'b1)

    forceEmpty <= 1'b1;

  else

    forceEmpty <= 1'b0;

end

//detect rising edge of 'forceEmpty', and generate toggle signal

always @(posedge busClk) begin

  if (rstSyncToBusClk == 1'b1) begin

    forceEmptyReg <= 1'b0;

    forceEmptyToggle <= 1'b0;

  end

  else begin

    if (forceEmpty == 1'b1)

      forceEmptyReg <= 1'b1;

    else

      forceEmptyReg <= 1'b0;

    if (forceEmpty == 1'b1 && forceEmptyReg == 1'b0)

      forceEmptyToggle <= ~forceEmptyToggle;

  end

end

assign forceEmptySyncToBusClk = (forceEmpty == 1'b1 && forceEmptyReg == 1'b0) ? 1'b1 : 1'b0;

// double sync across clock domains to generate 'forceEmptySyncToUsbClk'

always @(posedge usbClk) begin

    forceEmptyToggleSyncToUsbClk <= {forceEmptyToggleSyncToUsbClk[1:0], forceEmptyToggle};

end

assign forceEmptySyncToUsbClk = forceEmptyToggleSyncToUsbClk[2] ^ forceEmptyToggleSyncToUsbClk[1];

// async read mux

always @(address or fifoDataIn or numElementsInFifo)

begin

  case (address)

      `FIFO_DATA_REG : busDataOut <= fifoDataIn;

      `FIFO_DATA_COUNT_MSB : busDataOut <= numElementsInFifo[15:8];

      `FIFO_DATA_COUNT_LSB : busDataOut <= numElementsInFifo[7:0];

      default: busDataOut <= 8'h00;

  endcase

end

//generate fifo read strobe

always @(address or writeEn or strobe_i or fifoSelect) begin

  if (address == `FIFO_DATA_REG &&   writeEn == 1'b0 &&

  strobe_i == 1'b1 &&   fifoSelect == 1'b1)

    fifoREn <= 1'b1;

  else

    fifoREn <= 1'b0;

end

endmodule