ph_meter.v

Clock data recovery .........good example

///////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2003 Xilinx, Inc.
// All Rights Reserved
///////////////////////////////////////////////////////////////////////////////
//   ____  ____
//  /   /\/   /
// /___/  \  /    Vendor: Xilinx
// \   \   \/     Version: 1.0
//  \   \         Application : XAPP868
//  /   /         Filename: ph_meter.v
// /___/   /\     Timestamp: Thu Jan 17 2008
// \   \  /  \
//  \___\/\___\
//
///////////////////////////////////////////////////////////////////////////////
`timescale 1ns / 1ps

module ph_meter(in_sig_1, in_sig_2);
   input   in_sig_1;
   input   in_sig_2;
   //output time out_ph1;
   
   real phase;
   reg  alt=0;
   real out_ph1;
   real strt;
   real stp;
   
   always @( in_sig_1)
   begin: xhdl0
      //time    strt;
      //time    stp;
      //time    diff;
      
        
      if (in_sig_1 == 1'b1 & ~(alt))
      begin
         strt = $realtime;
         alt = 1;
      end
   end
   
   always @( in_sig_2)
   begin: xhdl1  
      if (in_sig_2 == 1'b1 & (alt)& $realtime>strt)
      //if (in_sig_2 == 1'b1 & $realtime>strt)
      begin
        stp = $realtime;
        
	     phase = (stp-strt)/0.5e3;
	     alt = 0;
      end
   assign out_ph1 = phase;
   end  
endmodule