Subversion Repositories dpll-isdn

/* Random Walk Filter with reset value of 0*/

module randomwalkfilter(MainClock, Lead, Lag, Positive, Negative);

 input  MainClock, Lead, Lag;    // System Clock and Phase Comparator signals

 output Positive, Negative;      // "positive shift" and "negative shift" outputs

/* some parametere are accessible from outside */

parameter FilterLength      = 8;

parameter FilterResetValue  = 4;

parameter FilterMaxValue    = FilterResetValue;

parameter FilterMinValue    = 256 - FilterResetValue;

/* reversive counter */

reg [FilterLength-1 : 0] FilterCounter;

/* calculation of output pulses synchrinized with MainClock */

always @(posedge MainClock)

 begin

  if((FilterCounter == FilterMaxValue) || (FilterCounter == FilterMinValue))

    FilterCounter <= 0;

    else

     begin

      if(Lead) FilterCounter <= FilterCounter + 1;

      if(Lag)  FilterCounter <= FilterCounter - 1;

     end

 end

/* making "Lead" and "Lag" signals when  */

/* counter reached max or min levels     */

reg Positive, Negative;

always @(posedge MainClock)

 begin

  Positive <= (FilterCounter == FilterMaxValue);

  Negative <= (FilterCounter == FilterMinValue);

 end

endmodule