----------------------------------------------------------------------------------
-- Company:        ETH Zurich, Institute for Particle Physics
-- Engineer:       Patrick Vogler
-- 
-- Create Date:    March 11  2011
-- Design Name:    
-- Module Name:    FTM Timing counter
-- Project Name: 
-- Target Devices: 
-- Tool versions: 
-- Description:    48 bit counter for time stamping and on-time counting
--
-- Dependencies: 
--
-- Revision: 
-- Revision 0.01 - File Created
-- Additional Comments: 
--
--
-- modifications:
--
-- April 12 2011 by Patrick Vogler
--
-- May 18 2011 by Patrick Vogler
----------------------------------------------------------------------------------

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;

---- Uncomment the following library declaration if instantiating
---- any Xilinx primitives in this code.
library UNISIM;
use UNISIM.VComponents.all;

library ftm_definitions;
USE ftm_definitions.ftm_array_types.all;
USE ftm_definitions.ftm_constants.all;



entity Timing_counter is
  port(
   
-- Clock
-------------------------------------------------------------------------------
   clk              : in   STD_LOGIC;       -- 50 MHz system clock

   enable           : in   STD_LOGIC;       -- enable counter
   reset            : in   Std_LOGIC;       -- reset counter

   -- handshake signal
   read_counter     : in   STD_LOGIC;       -- read counter
   reading_started  : out  STD_LOGIC;
   reading_valid    : out  STD_LOGIC;       -- counter reading at output ready

   -- counter reading
   counter_reading  : out  std_logic_vector (TC_WIDTH - 1 downto 0)   
  );
end Timing_counter; 



architecture Behavioral of Timing_counter is

type type_read_counter_state is (IDLE, COPY, SET_VALID, RESET_STARTED);   
signal read_counter_state       : type_read_counter_state  := IDLE;   
  
signal counting            : std_logic_vector (TC_WIDTH - 1       downto 0);
signal counter_reading_sig : std_logic_vector (TC_WIDTH - 1       downto 0);
signal precounting         : std_logic_vector (PRECOUNT_WIDTH - 1 downto 0);


begin
--  counting
-------------------------------------------------------------------------------
  count :  process (clk, reset, enable)
  begin 
    if reset = '1' then
	 counting    <= (others => '0');
	 precounting <= (others => '0');
		 
       elsif rising_edge(clk) then 
           if enable = '1' then
              precounting <= precounting + 1;
              if (precounting = PRECOUNT_DIVIDER) then         
                counting <= counting + 1;
                precounting <= (others => '0');       		 
              end if;          
       end if;       
    end if;   
  end process count;


-- read counter
-------------------------------------------------------------------------------
  readout_counter : process (clk, read_counter)
  begin
    if rising_edge(clk) then
       case read_counter_state is

         when IDLE =>
              if read_counter = '1' then 
                 reading_valid <= '0';
                 reading_started <= '1'; 
                 read_counter_state <= COPY;
              end if;
                       
         when COPY =>
              counter_reading_sig <= counting;		  
	      read_counter_state <= SET_VALID;

         when SET_VALID =>               
              read_counter_state <= RESET_STARTED;

         when RESET_STARTED =>
              if read_counter = '0' then 
                 reading_started <= '0';
                 reading_valid <= '1';
                 read_counter_state <= IDLE;
              end if;
                
       end case;           
    end if;  
end process readout_counter; 
	  	 
counter_reading <= counter_reading_sig;

end Behavioral;