verilog/rtl/lib/clk_ctl.v

//////////////////////////////////////////////////////////////////////
////                                                              ////
////  Tubo 8051 cores common library Module                       ////
////                                                              ////
////  This file is part of the Turbo 8051 cores project           ////
////  http://www.opencores.org/cores/turbo8051/                   ////
////                                                              ////
////  Description                                                 ////
////  Turbo 8051 definitions.                                     ////
////                                                              ////
////  To Do:                                                      ////
////    nothing                                                   ////
////                                                              ////
////  Author(s):                                                  ////
////      - Dinesh Annayya, dinesha@opencores.org                 ////
////                                                              ////
////  Revision : Mar 2, 2011                                      //// 
////                                                              ////
//////////////////////////////////////////////////////////////////////
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//// Copyright (C) 2000 Authors and OPENCORES.ORG                 ////
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//// You should have received a copy of the GNU Lesser General    ////
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//////////////////////////////////////////////////////////////////////

// #################################################################
// Module: clk_ctl
//
// Description:  Generic clock control logic , clk-out = mclk/(2+clk_div_ratio)
//
//  
// #################################################################


module clk_ctl (
   // Outputs
       clk_o,
   // Inputs
       mclk,
       reset_n, 
       clk_div_ratio 
   );

//---------------------------------
// CLOCK Default Divider value.
// This value will be change from outside
//---------------------------------
parameter  WD = 'h1;

//---------------------------------------------
// All the input to this block are declared here
// --------------------------------------------
   input        mclk          ;// 
   input        reset_n       ;// primary reset signal
   input [WD:0] clk_div_ratio ;// primary clock divide ratio
                               // output clock = selected clock / (div_ratio+1)
   
//---------------------------------------------
// All the output to this block are declared here
// --------------------------------------------
   output       clk_o             ; // clock out

               

//------------------------------------
// Clock Divide func is done here
//------------------------------------
reg  [WD-1:0]    high_count       ; // high level counter
reg  [WD-1:0]    low_count        ; // low level counter
reg              mclk_div         ; // divided clock


assign clk_o  = mclk_div;

always @ (posedge mclk or negedge reset_n)
begin // {
   if(reset_n == 1'b0) 
   begin 
      high_count  <= 'h0;
      low_count   <= 'h0;
      mclk_div    <= 'b0;
   end   
   else 
   begin 
      if(high_count != 0)
      begin // {
         high_count    <= high_count - 1;
         mclk_div      <= 1'b1;
      end   // }
      else if(low_count != 0)
      begin // {
         low_count     <= low_count - 1;
         mclk_div      <= 1'b0;
      end   // }
      else
      begin // {
         high_count    <= clk_div_ratio[WD:1] + clk_div_ratio[0];
         low_count     <= clk_div_ratio[WD:1] + 1;
         mclk_div      <= ~mclk_div;
      end   // }
   end   // }
end   // }


endmodule