source: firmware/FTM/Timing_counters/Timing_counter.vhd@ 12521

----------------------------------------------------------------------------------
-- 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
--
-- May 20, 2011, by Q. Weitzel
-- counting was wrong by one clock cycle (1 us)
--
-- May 23, 2011, by Q. Weitzel
-- counter reset changed from async to sync reset
-- reset, enable and read_counter removed from sensitity lists
--
----------------------------------------------------------------------------------

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) := (others => '0');
signal counter_reading_sig : std_logic_vector (TC_WIDTH - 1       downto 0) := (others => '0');
signal precounting         : std_logic_vector (PRECOUNT_WIDTH - 1 downto 0) := (others => '0');


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

-- read counter
-------------------------------------------------------------------------------
  readout_counter : process (clk)
  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;