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-------------------------------------------------------------------------------

-- Title      : Write pulse synchronizer for Mixed clock FIFO

-- Project    :

-------------------------------------------------------------------------------

-- File       : 

-- Author     : kulmala3

-- Created    : 16.12.2005

-- Last update: 18.12.2006

-- Description: Re faster than WE

-------------------------------------------------------------------------------

-- Copyright (c) 2005

-- one p may be a bit suspicious if blindly trusted. should not be used.

-------------------------------------------------------------------------------

-- Revisions  :

-- Date        Version  Author  Description

-- 16.12.2005  1.0      AK      Created

-------------------------------------------------------------------------------

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_arith.all;

use ieee.std_logic_unsigned.all;

entity we_pulse_synchronizer is

  generic (

    data_width_g : integer := 0

    );

  port (

    clk_re    : in std_logic;   -- THIS IS ALWAYS THE FASTER CLOCK!!!

    clk_ps_re : in std_logic;           -- phase shifted pulse

    clk_we    : in std_logic;

    clk_ps_we : in std_logic;           -- phase shifted pulse

    rst_n     : in std_logic;

    -- to synchronize clk_we -> clk_re

    data_in   : in  std_logic_vector (data_width_g-1 downto 0);

    we_in     : in  std_logic;

    full_out  : out std_logic;

    one_p_out : out std_logic;

    -- from synchronization to clk_re, we pulse width adjusted

    data_out  : out std_logic_vector (data_width_g-1 downto 0);

    we_out     : out  std_logic;

    -- From clk_re domain FIFO

    full_in : in std_logic;

    one_p_in : in std_logic

    );

end we_pulse_synchronizer;

architecture rtl of we_pulse_synchronizer is

  signal data_to_fifo : std_logic_vector (data_width_g-1 downto 0);

  signal we_to_fifo   : std_logic;

  signal we_local_r   : std_logic;

  signal clk_we_was_r : std_logic;

  signal data_between_r  : std_logic_vector (data_width_g-1 downto 0);

  signal we_between_r    : std_logic;

  signal full_between_r  : std_logic;

  signal one_p_between_r : std_logic;

  signal full_from_fifo  : std_logic;

  signal one_p_from_fifo : std_logic;

  signal full_out_r      : std_logic;

  signal clk_we_period_r : std_logic;

  signal derived_clk : std_logic;

begin  -- rtl

  full_out  <= full_out_r;              --from_fifo;

  data_out <= data_to_fifo;

  we_out <= we_to_fifo;

  one_p_from_fifo <= one_p_in;

  full_from_fifo <= full_in;

  refaster : process (clk_we, rst_n)

  begin  -- process refaster

    if rst_n = '0' then                 -- asynchronous reset (active low)

      full_out_r     <= '1';

      data_between_r <= (others => '0');

      we_between_r   <= '0';

    elsif clk_we'event and clk_we = '1' then  -- rising clock edge

      if full_between_r = '0' then

        data_between_r <= data_in;

        we_between_r   <= we_in;

      end if;

      full_out_r <= full_between_r or one_p_between_r;

    end if;

  end process refaster;

  derived_clk <= (clk_ps_we nand clk_ps_re) and clk_we;

  derclk : process (derived_clk, rst_n)

  begin  -- process derclk

    if rst_n = '0' then                 -- asynchronous reset (active low)

      data_to_fifo    <= (others => '0');

      we_local_r      <= '0';

      full_between_r  <= '0';

      one_p_between_r <= '0';

      clk_we_period_r <= '0';

    elsif derived_clk'event and derived_clk = '1' then  -- rising clock edge

      if full_from_fifo = '0' then

        data_to_fifo <= data_between_r;

        we_local_r   <= we_between_r;

      else

        we_local_r <= '0';

      end if;

      full_between_r  <= full_from_fifo;

      one_p_between_r <= one_p_from_fifo;

      clk_we_period_r <= not clk_we_period_r;

    end if;

  end process derclk;

  one_p_out <= one_p_between_r;         -- follows one_p_between.

  we_to_fifo <= (clk_we_period_r xor clk_we_was_r) and we_local_r;

  process (clk_re, rst_n)

  begin  -- process

    if rst_n = '0' then                 -- asynchronous reset (active low)

      clk_we_was_r <= '0';

    elsif clk_re'event and clk_re = '1' then  -- rising clock edge

      clk_we_was_r <= clk_we_period_r;

    end if;

  end process;

end rtl;