-----By RAHUL SINGHAL----
----This is the code of a FSM that implements a toll booth -
----controller


LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL; ----using all functions of 
specific package---

ENTITY tollbooth2 IS
   PORT (Clock,car_s,RE : IN STD_LOGIC;
         coin_s         : IN STD_LOGIC_VECTOR(1 DOWNTO 0);
         r_light,g_light,alarm : OUT STD_LOGIC);
END tollbooth2;

ARCHITECTURE Behav OF tollbooth2 IS
TYPE state_type IS 
(NO_CAR,GOTZERO,GOTFIV,GOTTEN,GOTFIF,GOTTWEN,CAR_PAID,CHEATE
D);
------GOTZERO = PAID $0.00--------- 
------GOTFIV = PAID $0.05----------
------GOTTEN = PAID $0.10----------
------GOTFIF = PAID $0.15----------
------GOTTWEN = PAID $0.20---------
SIGNAL present_state,next_state : state_type;

BEGIN
-----Next state is identified using present state,car & 
coin sensors------
    PROCESS(present_state,car_s,coin_s)
     BEGIN
     
     CASE present_state IS
      WHEN NO_CAR =>
       IF (car_s = '1') THEN
           next_state <= GOTZERO;
        ELSE 
           next_state <= NO_CAR;
       END IF;

     WHEN GOTZERO =>
      IF (car_s ='0') THEN
      next_state <= CHEATED;
        ELSIF (coin_s = "00") THEN
        next_state <= GOTZERO;
        ELSIF (coin_s = "01") THEN
         next_state <= GOTFIV;
        ELSIF (coin_s ="10") THEN
         next_state <= GOTTEN;
      END IF;

    WHEN GOTFIV=>
     IF (car_s ='0') THEN
      next_state <= CHEATED;
       ELSIF (coin_s = "00") THEN
       next_state <= GOTFIV;
  
       ELSIF (coin_s = "01") THEN
        next_state <= GOTTEN;
       ELSIF (coin_s <= "10") THEN
        next_state <= GOTFIV;
    END IF;

   WHEN GOTTEN =>
    IF (car_s ='0') THEN
      next_state <= CHEATED;
      ELSIF (coin_s ="00") THEN
      next_state <= GOTTEN;
      
      ELSIF (coin_s="01") THEN
         next_state <= GOTFIV;
      ELSIF (coin_s="10") THEN
         next_state <= GOTTWEN;
    END IF;

   WHEN GOTFIF =>
    IF (car_s ='0') THEN
       next_state <= CHEATED; 
       ELSIF (coin_s = "00") THEN
       next_state <= GOTFIF;
      
       ELSIF (coin_s ="01") THEN
           next_state <= GOTTWEN;
       ELSIF (coin_s = "10") THEN
           next_state <= GOTTWEN;
     END IF;

   WHEN GOTTWEN =>
      next_state <= CAR_PAID;

   WHEN CAR_PAID =>
    IF (car_s = '0') THEN
      next_state <= NO_CAR;
     ELSE
      next_state<= CAR_PAID;
   END IF;
 
  WHEN CHEATED =>
      IF (car_s = '1') THEN
      next_state <= GOTZERO;
      ELSE 
      next_state <= CHEATED;
  END IF;

END CASE;
END PROCESS;-----End of Process 1
-------PROCESS 2 for STATE REGISTER CLOCKING--------
PROCESS(Clock,RE)
  BEGIN
   IF RE = '1' THEN
      present_state <= GOTZERO;
----When the clock changes from low to high,the state of 
the system
----stored in next_state becomes the present state----- 
       ELSIF Clock'EVENT AND Clock ='1' THEN
      present_state <= next_state;
   END IF; 
  END PROCESS;-----End of Process 2-------
---------------------------------------------------------
-----Conditional signal assignment statements----------
r_light <= '0' WHEN present_state = CAR_PAID ELSE '1';
g_light <= '1' WHEN present_state = CAR_PAID ELSE '0';
alarm <= '1' WHEN present_state = CHEATED ELSE '0';
END Behav;