library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
 
entity tutorial_led_blink is
  port (
    i_clock      : in  std_logic;
    i_enable     : in  std_logic;
    i_switch_1   : in  std_logic;
    i_switch_2   : in  std_logic;
    o_led_drive  : out std_logic
    );
end tutorial_led_blink;
 
architecture rtl of tutorial_led_blink is
 
  -- Constants to create the frequencies needed:
  -- Formula is: (25 MHz / 100 Hz * 50% duty cycle)
  -- So for 100 Hz: 25,000,000 / 100 * 0.5 = 125,000
  constant c_CNT_100HZ : natural := 125000;
  constant c_CNT_50HZ  : natural := 250000;
  constant c_CNT_10HZ  : natural := 1250000;
  constant c_CNT_1HZ   : natural := 12500000;
 
 
  -- These signals will be the counters:
  signal r_CNT_100HZ : natural range 0 to c_CNT_100HZ;
  signal r_CNT_50HZ  : natural range 0 to c_CNT_50HZ;
  signal r_CNT_10HZ  : natural range 0 to c_CNT_10HZ;
  signal r_CNT_1HZ   : natural range 0 to c_CNT_1HZ;
   
  -- These signals will toggle at the frequencies needed:
  signal r_TOGGLE_100HZ : std_logic := '0';
  signal r_TOGGLE_50HZ  : std_logic := '0';
  signal r_TOGGLE_10HZ  : std_logic := '0';
  signal r_TOGGLE_1HZ   : std_logic := '0';
 
  -- One bit select wire.
  signal w_LED_SELECT : std_logic;
   
begin
 
  -- All processes toggle a specific signal at a different frequency.
  -- They all run continuously even if the switches are
  -- not selecting their particular output.
   
  p_100_HZ : process (i_clock) is
  begin
    if rising_edge(i_clock) then
      if r_CNT_100HZ = c_CNT_100HZ-1 then  -- -1, since counter starts at 0
        r_TOGGLE_100HZ <= not r_TOGGLE_100HZ;
        r_CNT_100HZ    <= 0;
      else
        r_CNT_100HZ <= r_CNT_100HZ + 1;
      end if;
    end if;
  end process p_100_HZ;
 
 
  p_50_HZ : process (i_clock) is
  begin
    if rising_edge(i_clock) then
      if r_CNT_50HZ = c_CNT_50HZ-1 then  -- -1, since counter starts at 0
        r_TOGGLE_50HZ <= not r_TOGGLE_50HZ;
        r_CNT_50HZ    <= 0;
      else
        r_CNT_50HZ <= r_CNT_50HZ + 1;
      end if;
    end if;
  end process p_50_HZ;
 
   
  p_10_HZ : process (i_clock) is
  begin
    if rising_edge(i_clock) then
      if r_CNT_10HZ = c_CNT_10HZ-1 then  -- -1, since counter starts at 0
        r_TOGGLE_10HZ <= not r_TOGGLE_10HZ;
        r_CNT_10HZ    <= 0;
      else
        r_CNT_10HZ <= r_CNT_10HZ + 1;
      end if;
    end if;
  end process p_10_HZ;
 
   
  p_1_HZ : process (i_clock) is
  begin
    if rising_edge(i_clock) then
      if r_CNT_1HZ = c_CNT_1HZ-1 then  -- -1, since counter starts at 0
        r_TOGGLE_1HZ <= not r_TOGGLE_1HZ;
        r_CNT_1HZ    <= 0;
      else
        r_CNT_1HZ <= r_CNT_1HZ + 1;
      end if;
    end if;
  end process p_1_HZ;
 
   
  -- Create a multiplexor based on switch inputs
  w_LED_SELECT <= r_TOGGLE_100HZ when (i_switch_1 = '0' and i_switch_2 = '0') else
                  r_TOGGLE_50HZ  when (i_switch_1 = '0' and i_switch_2 = '1') else
                  r_TOGGLE_10HZ  when (i_switch_1 = '1' and i_switch_2 = '0') else
                  r_TOGGLE_1HZ;
 
   
  -- Only allow o_led_drive to drive when i_enable is high (and gate).
  o_led_drive <= w_LED_SELECT and i_enable;
 
end rtl;