source: firmware/FTM/trigger/drivers/time_window/time_counter.vhd@ 13417

--=======================================================================================
-- TITLE        : Timer
-- DESCRIPTION  : Timer for time coincidence windows
-- FILE         : time_counter.vhd
-- COMPANY      : Micro-Cameras & Space Exploration SA
--=======================================================================================
-- CREATION
-- DATE                         AUTHOR  PROJECT                 REVISION
-- 02/03/2011 JGi     FTM        110302a
--=======================================================================================
-- MODIFICATION HISTORY
-- DATE                         AUTHOR  PROJECT                 REVISION        COMMENTS
-- 02/03/2011 JGi               FTM         110302a     Description
--=======================================================================================
-- Library Definition
library ieee;
  use ieee.std_logic_1164.all;
  use ieee.numeric_std.all;

-- Entity Definition
entity time_counter is
  port( --clock
        clk_250MHz      : in  std_logic;
        --control
        enable                  : in    std_logic;
        window                  : in    std_logic_vector(3 downto 0);
        --I/O
        start_rise      : in    std_logic;
        start_fall      : in    std_logic;
        counting                :       out     std_logic);
end time_counter;

-- Architecture Definition
architecture RTL of time_counter is

  type t_reg is record
    -- Internal register declaration
    enable              : std_logic;
    started             : std_logic;
    done                        : std_logic;
    window              : unsigned(3 downto 0);
    counter             : unsigned(3 downto 0);
    -- Ouput register declaration
    counting    : std_logic;
  end record;

  signal i_next_reg : t_reg     := (enable              => '0',
                                                                                                                        started         => '0',
                                                                                                                        done                    => '0',
                                                                                                                        window          => (others => '0'),
                                                                                                                        counter         => (others => '0'),
                                                                                                                        counting        => '0');
  signal i_reg      : t_reg     := (enable              => '0',
                                                                                                                        started         => '0',
                                                                                                                        done                    => '0',
                                                                                                                        window          => (others => '0'),
                                                                                                                        counter         => (others => '0'),
                                                                                                                        counting        => '0');

begin

  -- Combinatorial logic
  process(enable, window, start_rise, start_fall, i_reg)
    variable v_reg  : t_reg     := (enable              => '0',
                                                                                                                        started         => '0',
                                                                                                                        done                    => '0',
                                                                                                                        window          => (others => '0'),
                                                                                                                        counter         => (others => '0'),
                                                                                                                        counting        => '0');
  begin
    v_reg := i_reg;
    --===================================================================================

    --===================================================================================
    -- Counter management
    --===================================================================================
    -- Register activation signal (From active FTU list)
    v_reg.enable        := enable;
    -- Register window width to improve speed
    v_reg.window        := unsigned(window);
    -- Register enables to detect rising edges on them
    v_reg.started       := start_rise or start_fall;

                -- Counter is counting permanently
                v_reg.counter   := i_reg.counter+1;

                -- If enabled and input rising edge, reset counter
    if i_reg.enable = '1' and (start_rise = '1' or start_fall = '1') and
    i_reg.started = '0' then
        v_reg.counting  := '1';
        v_reg.counter           := (others => '0');
    end if;

                v_reg.done      := '0';
                -- If inputs rised and counter reahc the value then done
                if i_reg.counter = i_reg.window and i_reg.counting = '1' then
        v_reg.done      := '1';
    end if;

                -- Disable counter comparison if done
    if i_reg.done = '1' then
        v_reg.counting  := '0';
    end if;
    --===================================================================================

    --===================================================================================
    -- Drive register input
    i_next_reg <= v_reg;

    --===================================================================================
    -- Output assignation
                counting        <= i_reg.counting;
    --===================================================================================
  end process;

  -- Sequential logic
  process(clk_250MHz)
  begin
    if rising_edge(clk_250MHz) then
      i_reg <= i_next_reg;
    end if;
  end process;

end RTL;