usb1_fifo2.v

usb1.1 ip核

/////////////////////////////////////////////////////////////////////
////                                                             ////
////  Fast FIFO 2 entries deep                                   ////
////                                                             ////
////                                                             ////
////  Author: Rudolf Usselmann                                   ////
////          [e-mail]                                      ////
////                                                             ////
////                                                             ////
////  Downloaded from: http://www.opencores.org/cores/usb1_funct/////
////                                                             ////
/////////////////////////////////////////////////////////////////////
////                                                             ////
//// Copyright (C) 2000-2002 Rudolf Usselmann                    ////
////                         www.asics.ws                        ////
////                         [e-mail]                       ////
////                                                             ////
//// 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 SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY     ////
//// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED   ////
//// TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS   ////
//// FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL THE AUTHOR      ////
//// OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,         ////
//// INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES    ////
//// (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE   ////
//// GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR        ////
//// BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF  ////
//// LIABILITY, WHETHER IN  CONTRACT, STRICT LIABILITY, OR TORT  ////
//// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT  ////
//// OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE         ////
//// POSSIBILITY OF SUCH DAMAGE.                                 ////
////                                                             ////
/////////////////////////////////////////////////////////////////////

//  CVS Log
//
//  $Id: usb1_fifo2.v,v 1.1.1.1 2002/09/19 12:07:31 rudi Exp $
//
//  $Date: 2002/09/19 12:07:31 $
//  $Revision: 1.1.1.1 $
//  $Author: rudi $
//  $Locker:  $
//  $State: Exp $
//
// Change History:
//               $Log: usb1_fifo2.v,v $
//               Revision 1.1.1.1  2002/09/19 12:07:31  rudi
//               Initial Checkin
//
//
//
//
//
//

`include "timescale.v"

module usb1_fifo2(clk, rst, clr,  din, we, dout, re);

input		clk, rst;
input		clr;
input   [7:0]	din;
input		we;
output  [7:0]	dout;
input		re;


////////////////////////////////////////////////////////////////////
//
// Local Wires
//

reg     [7:0]	mem[0:1];//定义了长度为两字节的8位存储器
reg		wp;
reg		rp;

////////////////////////////////////////////////////////////////////
//
// Misc Logic
//

always @(posedge clk or negedge rst)
        if(!rst)	wp <= #1 1'h0;
        else
        if(clr)		wp <= #1 1'h0;
        else
        if(we)		wp <= #1 ~wp;//取反放回，因为是两字节的才可这么轻松！！

always @(posedge clk or negedge rst)
        if(!rst)	rp <= #1 1'h0;
        else
        if(clr)		rp <= #1 1'h0;
        else
        if(re)		rp <= #1 ~rp;//取反放回

// Fifo Output
assign  dout = mem[ rp ];//无条件一直输出，输出仅由rp决定

// Fifo Input 
always @(posedge clk)
        if(we)     mem[ wp ] <= #1 din;

endmodule