module newfifo_2clock
  #(parameter DWIDTH=32, AWIDTH=9)
  (input wclk, input [DWIDTH-1:0] datain, input src_rdy_i, output dst_rdy_o, output reg [AWIDTH-1:0] level_wclk,
   input rclk, output [DWIDTH-1:0] dataout, output src_rdy_o, input dst_rdy_i, output reg [AWIDTH-1:0] level_rclk,
   input arst);

   wire full, empty, write, read;

   assign dst_rdy_o  = ~full;
   assign src_rdy_o  = ~empty;
   assign write      = src_rdy_i & dst_rdy_o;
   assign read 	     = src_rdy_o & dst_rdy_i;

//`define USE_XLNX_FIFO 1
`ifdef USE_XLNX_FIFO
   fifo_xlnx_512x36_2clk mac_tx_fifo_2clk
     (.rst(rst),
      .wr_clk(wclk),.din(datain),.full(full),.wr_en(write),.wr_data_count(fifo_occupied[8:0]),
      .rd_clk(rclk),.dout(dataout),.empty(empty),.rd_en(read),.rd_data_count() );   
`else
   // ISE sucks, so the following doesn't work properly

   reg [AWIDTH-1:0] wr_addr, rd_addr;
   wire [AWIDTH-1:0] wr_addr_rclk, rd_addr_wclk;
   wire [AWIDTH-1:0] next_rd_addr;
   wire 	    enb_read;
   
   // Write side management
   wire [AWIDTH-1:0] next_wr_addr = wr_addr + 1;
   always @(posedge wclk or posedge arst)
     if(arst)
       wr_addr <= 0;
     else if(write)
       wr_addr <= next_wr_addr;
   assign 	    full = (next_wr_addr == rd_addr_wclk);

   //  RAM for data storage.  Data out is registered, complicating the
   //     read side logic
   ram_2port #(.DWIDTH(DWIDTH),.AWIDTH(AWIDTH)) mac_rx_ff_ram
     (.clka(wclk),.ena(1'b1),.wea(write),.addra(wr_addr),.dia(datain),.doa(),
      .clkb(rclk),.enb(enb_read),.web(1'b0),.addrb(next_rd_addr),.dib(0),.dob(dataout) );

   // Read side management
   reg 		    data_valid;
   assign 	    empty = ~data_valid;
   assign 	    next_rd_addr = rd_addr + data_valid;
   assign 	    enb_read = read | ~data_valid;

   always @(posedge rclk or posedge arst)
     if(arst)
       rd_addr <= 0;
     else if(read)
       rd_addr <= rd_addr + 1;

   always @(posedge rclk or posedge arst)
     if(arst)
       data_valid <= 0;
     else
       if(read & (next_rd_addr == wr_addr_rclk))
	 data_valid <= 0;
       else if(next_rd_addr != wr_addr_rclk)
	 data_valid <= 1;
	 
   // Send pointers across clock domains via gray code
   gray_send #(.WIDTH(AWIDTH)) send_wr_addr
     (.clk_in(wclk),.addr_in(wr_addr),
      .clk_out(rclk),.addr_out(wr_addr_rclk) );
   
   gray_send #(.WIDTH(AWIDTH)) send_rd_addr
     (.clk_in(rclk),.addr_in(rd_addr),
      .clk_out(wclk),.addr_out(rd_addr_wclk) );

   // Generate fullness info, these are approximate and may be delayed 
   // and are only for higher-level flow control.  
   // Only full and empty are guaranteed exact.
   always @(posedge wclk) 
     level_wclk <= wr_addr - rd_addr_wclk;
   always @(posedge rclk) 
     level_rclk <= wr_addr_rclk - rd_addr;
`endif
endmodule // fifo_2clock