oh_fifo_cdc.v

//#############################################################################
//# Function: Clock domain crossing FIFO                                      #
//#############################################################################
//# Author:   Andreas Olofsson                                                #
//# License:  MIT (see LICENSE file in OH! repository)                        # 
//#############################################################################

module oh_fifo_cdc # (parameter DW        = 104,      //FIFO width
		      parameter DEPTH     = 32,       //FIFO depth (entries)
		      parameter TARGET    = "GENERIC" //XILINX,ALTERA,GENERIC
		      )
   (
   input 	   nreset, // shared domain async active low reset
   input 	   clk_in, // write clock
   input 	   access_in, // write access
   input [DW-1:0]  packet_in, // write packet
   output 	   wait_out, // write pushback
   input 	   clk_out, //read clock
   output reg 	   access_out, //read access
   output [DW-1:0] packet_out, //read packet
   input 	   wait_in, // read pushback
   output 	   prog_full, // fifo is half full
   output 	   full, // fifo is full
   output 	   empty // fifo is empty
    );
   
   // local wires
   wire 	   wr_en;
   wire 	   rd_en;
   wire 	   io_nreset;
      
   // parametric async fifo
   oh_fifo_async  #(.TARGET(TARGET),
		    .DW(DW),
		    .DEPTH(DEPTH))
   fifo (.prog_full (prog_full),
	 .full	    (full),
	 .rd_count  (),
	 .nreset    (nreset),
	 .dout	    (packet_out[DW-1:0]),
	 .empty	    (empty),
	 .wr_clk    (clk_in),
	 .rd_clk    (clk_out),
	 .wr_en	    (wr_en),
	 .din	    (packet_in[DW-1:0]),
	 .rd_en	    (rd_en));

   // FIFO control logic
   assign wr_en    = access_in;
   assign rd_en    = ~empty & ~wait_in;
   assign wait_out = prog_full;         //wait_out should stall access_in signal

   // pipeline access_out signal
   always @ (posedge clk_out or negedge io_nreset)
     if(!io_nreset)
       access_out <= 1'b0;   
     else if(~wait_in)
       access_out <= rd_en;
   
   // be safe, synchronize reset with clk_out
   oh_rsync sync_reset(.nrst_out  (io_nreset),
		       .clk	  (clk_out),
		       .nrst_in	  (nreset));
   
endmodule // oh_fifo_cdc