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--=============================================================================--

--                                                                             --

--  System09 - Synthesizable System On a Chip - XuLA System Clock DCM          --

--                                                                             --

--=============================================================================--

--

--

-- File name      : XuLA_clk.vhd

--

-- Entity name    : XuLA_clk

--

-- Purpose        : Clock module to generate 48MHz SDRAM clock

--                  and 24MHz CPU and VDU pixel clock 

--                  from the 12MHz PIC FPGA Clock

--

-- Dependencies   : ieee.Std_Logic_1164

--                  ieee.std_logic_unsigned

--                  ieee.std_logic_arith

--                  ieee.numeric_std

--

-- Uses           : 

--

-- Author         : John E. Kent      

--                  dilbert57@opencores.org      

--

--  Copyright (C) 2011 John Kent

--

--  This program is free software: you can redistribute it and/or modify

--  it under the terms of the GNU General Public License as published by

--  the Free Software Foundation, either version 3 of the License, or

--  (at your option) any later version.

--

--  This program is distributed in the hope that it will be useful,

--  but WITHOUT ANY WARRANTY; without even the implied warranty of

--  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

--  GNU General Public License for more details.

--

--  You should have received a copy of the GNU General Public License

--  along with this program.  If not, see <http://www.gnu.org/licenses/>.

--

--===========================================================================--

--

--                              Revision History:

--

--===========================================================================--

--

-- Version 0.1 - 30 April 2011 - John Kent

-- Initial version

--

library ieee;

   use ieee.std_logic_1164.all;

   use IEEE.STD_LOGIC_ARITH.ALL;

   use IEEE.STD_LOGIC_UNSIGNED.ALL;

   use ieee.numeric_std.all;

library unisim;

   use unisim.vcomponents.all;

Entity XuLA_clk is

  generic(

        FPGA_CLK_FREQ          : integer := 12000000; -- HZ

             CPU_CLK_FREQ           : integer := 24000000; -- Hz

             VDU_CLK_FREQ           : integer := 24000000; -- Hz

                  RAM_CLK_FREQ           : integer := 48000000 -- Hz

  );

  port(

    fpga_clk     : in  std_logic;      -- 12MHz FPGA Clock

    cpu_clk      : out std_logic;      -- 24MHz CPU clock

    vdu_clk      : out std_logic;      -- 24MHz VDU clock

         ram_clk      : out std_logic       -- 48MHz RAM clock

    );

end XuLA_clk;

Architecture RTL of XuLA_clk is

signal clk12_dcm : std_logic;

signal clk24_dcm : std_logic;

signal clk48_dcm : std_logic;

component BUFG

  port (

    I : in  std_logic;

    O : out std_logic

  );

end component;

begin

  DCM_XuLA_inst : DCM

   generic map (

     DLL_FREQUENCY_MODE    => "LOW", -- "LOW" or "HIGH" 

     CLKIN_PERIOD          => 83.3,  -- in nsec 

     CLKFX_DIVIDE          => 1,

     CLKFX_MULTIPLY        => 4,

          CLKDV_DIVIDE          => 2,

     CLKIN_DIVIDE_BY_2     => FALSE,

     CLKOUT_PHASE_SHIFT    => "NONE",

     CLK_FEEDBACK          => "1X",

     DESKEW_ADJUST         => "SYSTEM_SYNCHRONOUS",

     DFS_FREQUENCY_MODE    => "LOW",

     DUTY_CYCLE_CORRECTION => TRUE,

     FACTORY_JF            => X"8080",

     PHASE_SHIFT           => 0,

     STARTUP_WAIT          => FALSE)

   port map (

     CLKIN      => fpga_clk,     -- input 12MHz

     CLKFB      => clk12_dcm,    -- feedback input 

     CLK0       => clk12_dcm,    -- Feedback output (phase, freq = input) 

     CLK90      => open,         -- Feedback output +  90deg

     CLK180     => open,         -- Feedback output + 180deg 

     CLK270     => open,         -- Feedback output + 270deg

     CLK2X      => clk24_dcm,    -- 2 x input Freq Output 

     CLK2X180   => open,         -- 2 x input Freq Output + 180 deg

     CLKDV      => open,         -- Fclkdv = Fclkin/CLKDV_DIVIDE 

     CLKFX      => clk48_dcm,    -- Fclkfx = Fclkin*CLKFX_MULIPLY/CLKFX_DIVIDE 

     CLKFX180   => open,         -- CLKFX180 = CLKFX + 180 degrees 

     LOCKED     => open,         -- DCM in lock 

     PSDONE     => open,

     STATUS     => open,

     PSCLK      => open,         -- Clock input to dynamic phase shifter 

     PSEN       => open,

     PSINCDEC   => open,

     RST        => '0'

   );

  bufram : BUFG port map(

               I => clk48_dcm,

               O => ram_clk

              );

  bufcpu : BUFG port map (

               I => clk24_dcm,

               O => cpu_clk

              );

  bufvdu : BUFG port map (

               I => clk24_dcm,

               O => vdu_clk

              );

end RTL;