VHDL code for traffic light controller

-- VHDL project: VHDL code for traffic light controller
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
-- Traffic ligh system for a intersection between highway and farm way
-- There is a sensor on the farm way side, when there are vehicles,
-- Traffic light turns to YELLOW, then GREEN to let the vehicles cross the highway
-- Otherwise, always green light on Highway and Red light on farm way
entity traffic_light_controller is
 port ( sensor  : in STD_LOGIC; -- Sensor
        clk  : in STD_LOGIC; -- clock
        rst_n: in STD_LOGIC; -- reset active low
        light_highway  : out STD_LOGIC_VECTOR(2 downto 0); -- light outputs of high way
     light_farm:    out STD_LOGIC_VECTOR(2 downto 0)-- light outputs of farm way
     --RED_YELLOW_GREEN
   );
end traffic_light_controller;
architecture traffic_light of traffic_light_controller is
signal counter_1s: std_logic_vector(27 downto 0):= x"0000000";
signal delay_count:std_logic_vector(3 downto 0):= x"0";
signal delay_10s, delay_3s_F,delay_3s_H, RED_LIGHT_ENABLE, YELLOW_LIGHT1_ENABLE,YELLOW_LIGHT2_ENABLE: std_logic:='0';
signal clk_1s_enable: std_logic; -- 1s clock enable
type FSM_States is (HGRE_FRED, HYEL_FRED, HRED_FGRE, HRED_FYEL);
-- HGRE_FRED : Highway green and farm red
-- HYEL_FRED : Highway yellow and farm red
-- HRED_FGRE : Highway red and farm green
-- HRED_FYEL : Highway red and farm yellow
signal current_state, next_state: FSM_States;
begin
-- next state FSM sequential logic
process(clk,rst_n)
begin
if(rst_n='0') then
 current_state <= HGRE_FRED;
elsif(rising_edge(clk)) then
 current_state <= next_state;
end if;
end process;
-- FSM combinational logic
process(current_state,sensor,delay_3s_F,delay_3s_H,delay_10s)
begin
case current_state is
when HGRE_FRED => -- When Green light on Highway and Red light on Farm way
 RED_LIGHT_ENABLE <= '0';-- disable RED light delay counting
 YELLOW_LIGHT1_ENABLE <= '0';-- disable YELLOW light Highway delay counting
 YELLOW_LIGHT2_ENABLE <= '0';-- disable YELLOW light Farmway delay counting
 light_highway <= "001"; -- Green light on Highway
 light_farm <= "100"; -- Red light on Farm way
 if(sensor = '1') then -- if vehicle is detected on farm way by sensors
  next_state <= HYEL_FRED;
  -- High way turns to Yellow light
 else
  next_state <= HGRE_FRED;
  -- Otherwise, remains GREEN ON highway and RED on Farm way
 end if;
when HYEL_FRED => -- When Yellow light on Highway and Red light on Farm way
 light_highway <= "010";-- Yellow light on Highway
 light_farm <= "100";-- Red light on Farm way
 RED_LIGHT_ENABLE <= '0';-- disable RED light delay counting
 YELLOW_LIGHT1_ENABLE <= '1';-- enable YELLOW light Highway delay counting
 YELLOW_LIGHT2_ENABLE <= '0';-- disable YELLOW light Farmway delay counting
 if(delay_3s_H='1') then
 -- if Yellow light delay counts to 3s,
 -- turn Highway to RED,
 -- Farm way to green light
  next_state <= HRED_FGRE;
 else
  next_state <= HYEL_FRED;
  -- Remains Yellow on highway and Red on Farm way
  -- if Yellow light not yet in 3s
 end if;
when HRED_FGRE =>
 light_highway <= "100";-- RED light on Highway
 light_farm <= "001";-- GREEN light on Farm way
 RED_LIGHT_ENABLE <= '1';-- enable RED light delay counting
 YELLOW_LIGHT1_ENABLE <= '0';-- disable YELLOW light Highway delay counting
 YELLOW_LIGHT2_ENABLE <= '0';-- disable YELLOW light Farmway delay counting
 if(delay_10s='1') then
 -- if RED light on highway is 10s, Farm way turns to Yellow
  next_state <= HRED_FYEL;
 else
  next_state <= HRED_FGRE;
  -- Remains if delay counts for RED light on highway not enough 10s
 end if;
when HRED_FYEL =>
 light_highway <= "100";-- RED light on Highway
 light_farm <= "010";-- Yellow light on Farm way
 RED_LIGHT_ENABLE <= '0'; -- disable RED light delay counting
 YELLOW_LIGHT1_ENABLE <= '0';-- disable YELLOW light Highway delay counting
 YELLOW_LIGHT2_ENABLE <= '1';-- enable YELLOW light Farmway delay counting
 if(delay_3s_F='1') then
 -- if delay for Yellow light is 3s,
 -- turn highway to GREEN light
 -- Farm way to RED Light
 next_state <= HGRE_FRED;
 else
 next_state <= HRED_FYEL;
 -- if not enough 3s, remain the same state
 end if;
when others => next_state <= HGRE_FRED; -- Green on highway, red on farm way
end case;
end process;
-- Delay counts for Yellow and RED light
process(clk)
begin
if(rising_edge(clk)) then
if(clk_1s_enable='1') then
 if(RED_LIGHT_ENABLE='1' or YELLOW_LIGHT1_ENABLE='1' or YELLOW_LIGHT2_ENABLE='1') then
  delay_count <= delay_count + x"1";
  if((delay_count = x"9") and RED_LIGHT_ENABLE ='1') then
   delay_10s <= '1';
   delay_3s_H <= '0';
   delay_3s_F <= '0';
   delay_count <= x"0";
  elsif((delay_count = x"2") and YELLOW_LIGHT1_ENABLE= '1') then
   delay_10s <= '0';
   delay_3s_H <= '1';
   delay_3s_F <= '0';
   delay_count <= x"0";
  elsif((delay_count = x"2") and YELLOW_LIGHT2_ENABLE= '1') then
   delay_10s <= '0';
   delay_3s_H <= '0';
   delay_3s_F <= '1';
   delay_count <= x"0";
  else
   delay_10s <= '0';
   delay_3s_H <= '0';
   delay_3s_F <= '0';
  end if;
 end if;
 end if;
end if;
end process;
-- create delay 1s
process(clk)
begin
if(rising_edge(clk)) then
 counter_1s <= counter_1s + x"0000001";
 if(counter_1s >= x"0000003") then -- x"0004" is for simulation
 -- change to x"2FAF080" for 50 MHz clock running real FPGA
  counter_1s <= x"0000000";
 end if;
end if;
end process;
clk_1s_enable <= '1' when counter_1s = x"0003" else '0'; -- x"0002" is for simulation
-- x"2FAF080" for 50Mhz clock on FPGA
end traffic_light;