///////////2007.02.27 DPLL
module dpll(reset,clk,signal_in,signal_out,syn);//signalin=1.4us(best) to 1.28us,clk=10ns
parameter para_K=4;
parameter para_N=16;
input reset;
input clk;
input signal_in;
output signal_out;
output syn;
reg signal_out;
reg dpout;
reg delclk;
reg addclk;
reg add_del_clkout;
reg [7:0]up_down_cnt;
reg [2:0]cnt8;  //add or delate pulse
reg [8:0]cnt_N;
reg syn;
reg dpout_delay;
reg [8:0]cnt_dpout_high;
reg [8:0]cnt_dpout_low;


/******phase detector*****/
always@(signal_in or signal_out)
  begin
    dpout<=signal_in^signal_out;//edge detect
  end

/******synchronization establish detector*****/
always@(posedge clk or negedge reset)
  begin
        if(!reset)    dpout_delay<='b0;  //reset
        else          dpout_delay<=dpout;
  end
always@(posedge clk or negedge reset)
  begin
      if(!reset)
          begin 
            cnt_dpout_high<='b0; cnt_dpout_low<='b0;
          end
      else if(dpout)
                if(dpout_delay==0)  cnt_dpout_high<='b0;
                else
                    if(cnt_dpout_high==8'b11111111)  cnt_dpout_high<='b0;
                    else  cnt_dpout_high<=cnt_dpout_high+1;
      else if(!dpout)
                 if(dpout_delay==1)  cnt_dpout_low<='b0;
                 else
                     if(cnt_dpout_low==8'b11111111)  cnt_dpout_low<='b0;
                     else  cnt_dpout_low<=cnt_dpout_low+1;
   end
always@(posedge clk or negedge reset)
  begin
          if(!reset)  syn<='b0;
      else if((dpout&&!dpout_delay)||(!dpout&&dpout_delay))
           if(cnt_dpout_high[8:0]-cnt_dpout_low[8:0]<=4||cnt_dpout_low[8:0]-cnt_dpout_high[8:0]<=4)  syn<='b1;//no syn
           else  syn<='b0; //syn=ok
  end


/****up down couter with mod=K****/
always@(posedge clk or negedge reset)
begin
   if(!reset)
     begin 
       delclk<='b0;
       addclk<='b0;
       up_down_cnt<='b00000000;
     end
   else
     begin
       if(!dpout)
          begin
            delclk<='b0;
               if(up_down_cnt==para_K-1)
                  begin
                     up_down_cnt<='b00000000;
                     addclk<='b0;
                  end
                else
                  begin
                     up_down_cnt<=up_down_cnt+1;
                     addclk<='b0;
                   end
            end
         else
            begin
               addclk<='b0;
                  if(up_down_cnt=='b0)
                     begin
                        up_down_cnt<=para_K-1;
                        delclk<='b0;
                     end
                  else
                    if(up_down_cnt==1)
                       begin
                         delclk<='b1;
                         up_down_cnt<=up_down_cnt-1;
                       end
                    else
                       up_down_cnt<=up_down_cnt-1;
             end
        end
  end


/******add and delete clk*****/
always@(posedge clk or negedge reset)// add/ delate gate
begin
  if(!reset)  //reset=0
     begin
       cnt8<='b000;  //cnt8=0
     end
  else
     begin
       if(cnt8=='b111)//cnt8=0x07
         begin
            cnt8<='b000; //cnt8=0
         end
       else
          if(addclk&&!syn)   //add pulse
             begin
                cnt8<=cnt8+2;//add 1 pulse
             end
          else
             if(delclk&&!syn)
                cnt8<=cnt8;   // delate1 pulse
             else
                cnt8<=cnt8+1;  //no add /delate 
     end
end
always@(cnt8 or reset)
begin
if(!reset)
  add_del_clkout<='b0;
else
  add_del_clkout<=cnt8[2];
end


/******counter with mod=N******///fenpin N
always@(posedge add_del_clkout or negedge reset)
begin
  if(!reset)    //reset 
    begin
      cnt_N<='b0000;  //clear 0
      signal_out<='b0;
    end
  else
    begin
      if(cnt_N==para_N-1)
        begin
          cnt_N<='b0000;
          signal_out<='b0; //out 0
        end
      else
        if(cnt_N==(para_N-1)/2)    // at  N==(para_N-1)/2  out 1
           begin
             signal_out<='b1;  //out 1
             cnt_N<=cnt_N+1;
           end
        else
          cnt_N<=cnt_N+1;
    end
end
endmodule