-- ***************************************************************************
-- ***************************************************************************
-- Copyright 2013(c) Analog Devices, Inc.
--  Author: Lars-Peter Clausen <lars-peter.clausen@analog.com>
-- 
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-- ***************************************************************************

library ieee;
use ieee.std_logic_1164.all;

entity fifo_synchronizer is
	generic (
		DEPTH		: integer := 4;
		WIDTH		: integer := 2
	);
	port (

		in_clk	    : in std_logic;
		in_resetn   : in std_logic;
		in_data	    : in std_logic_vector(WIDTH - 1 downto 0);
		in_tick	    : in std_logic;

		out_clk	    : in std_logic;
		out_resetn  : in std_logic;
		out_data    : out std_logic_vector(WIDTH - 1 downto 0);
		out_tick    : out std_logic
	);

end fifo_synchronizer;

architecture impl of fifo_synchronizer is
	type DATA_SYNC_FIFO_TYPE is array (0 to DEPTH - 1) of std_logic_vector(WIDTH - 1 downto 0);
	signal fifo: DATA_SYNC_FIFO_TYPE;

	signal rd_addr : natural range 0 to DEPTH - 1;
	signal wr_addr : natural range 0 to DEPTH - 1;

	signal cdc_sync_stage0_tick : std_logic;
	signal cdc_sync_stage1_tick : std_logic;
	signal cdc_sync_stage2_tick : std_logic;
	signal cdc_sync_stage3_tick : std_logic;
	signal tick : std_logic;
begin

	process (in_clk)
	begin
		if rising_edge(in_clk) then
			if in_tick = '1' then
				cdc_sync_stage0_tick <= not cdc_sync_stage0_tick;
				fifo(wr_addr) <= in_data;
			end if;
		end if;
	end process;

	process (in_clk)
	begin
		if rising_edge(in_clk) then
			if in_resetn = '0' then
				wr_addr <= 0;
			else
				if in_tick = '1' then
					wr_addr <= (wr_addr + 1) mod DEPTH;
				end if;
			end if;
		end if;
	end process;

	process (out_clk)
	begin
		if rising_edge(out_clk) then
			cdc_sync_stage1_tick <= cdc_sync_stage0_tick;
			cdc_sync_stage2_tick <= cdc_sync_stage1_tick;
			cdc_sync_stage3_tick <= cdc_sync_stage2_tick;
		end if;
	end process;

	tick <= cdc_sync_stage2_tick xor cdc_sync_stage3_tick;
	out_tick <= tick;

	process (out_clk)
	begin
		if rising_edge(out_clk) then
			if tick = '1' then
				out_data <= fifo(rd_addr);
			end if;
		end if;
	end process;

	process (out_clk)
	begin
		if rising_edge(out_clk) then
			if out_resetn = '0' then
				rd_addr <= 0;
			else
				if tick = '1' then
					rd_addr <= (rd_addr + 1) mod DEPTH;
				end if;
			end if;
		end if;
	end process;
end;