Traffic Light Controller Objective This lab has these major objectives: 1) The understanding and implementing of indexed data structures; 2) Learning how to create a segmented software system; 3) The study of real-time synchronization by designing a finite state machine controller. Software skills you will learn include advanced indexed addressing, linked data structures, creating fixed-time delays using the SysTick timer, and debugging realtime systems. Please read the entire lab before starting. Also, read the FSM section in the textbook (or online book). Introduction Consider a 4-corner intersection as shown in Figure 1. There are two one-way streets are labeled South (cars travel South) and West (cars travel West). There are three inputs to your LaunchPad, two are car sensors, and one is a pedestrian sensor. The South car sensor will be true (3.3V) if one or more cars are near the intersection on the South road. Similarly, the West car sensor will be true (3.3V) if one or more cars are near the intersection on the West road. The Walk sensor will be true (3.3V) if a pedestrian is present and he or she wishes to cross in any direction. This walk sensor is different from a walk button on most real intersections. This means when you are testing the system, you must push and hold the walk sensor until the FSM recognizes the presence of the pedestrian. Similarly, you will have to push and hold the car sensor until the FSM recognizes the presence of the car. In this simple system, if the walk sensor is +3.3V, there is pedestrian to service, and if the walk sensor is 0V, there are no people who wish to walk. In a similar fashion, when a car sensor is 0V, it means no cars are waiting to enter the intersection. You will interface 6 LEDs that represent the two Red-Yellow-Green traffic lights, and you will use the PF3 green LED for the “walk” light and the PF1 red LED for the “don’t walk” light. When the “walk” condition is signified, pedestrians are allowed to cross. When the “don’t walk” light flashes (and the two traffic signals are red), pedestrians should hurry up and finish crossing. When the “don’t walk” condition is on steady, pedestrians should not enter the intersection. Figure 1: Traffic Light Intersection. Traffic should not be allowed to crash. I.e., there should not be only a green or only a yellow LED on one road at the same time there is only a green or only a yellow LED on the other road. You should exercise common sense when assigning the length of time that the traffic light will spend in each state. Each traffic light pattern must be on for at least ½ second but for at most 5 seconds. Cars should not be allowed to hit the pedestrians. The walk sequence should be realistic, showing three separate conditions: 1) “walk”, 2) “hurry up” using a flashing LED, and 3) “don’t walk”. You may assume the three sensors remain active for as long as service is required. The “hurry up” flashing should occur at least twice but at most 4 times. There is no single, “best” way to implement your system. A “good” solution will have about 9 to 30 states in the finite state machine and provides for input dependence. Try not to focus on the civil engineering issues. I.e., first build a quality computer engineering solution that is easy to understand and easy to change. Because we have three inputs, there will be 8 next state links. One way to draw the FSM graph to make it easier to read is to use X to signify don’t care. For example, compare the two FSM graphs in Figure 2. Drawing two arrows labeled 01 and 11 is the same as drawing one arrow with the label X1. South West R G Y R Y G G Walk Don’t walk PF3 PF1 R Walk Figure 2: FSM drawn with a short hand format (refer the textbook chapter 6 or online book). Procedure The basic approach to this lab will be to first develop and debug your system using the simulator. After the software is debugged, you will interface actual lights and switches to the LaunchPad and run your software on the real microcontroller. As you have experienced, the simulator requires different amount of actual time as compared to simulated time. On the other hand, the correct simulation time is maintained in the SysTick timer, which is decremented every cycle of simulation time. The simulator speed depends on the amount of information it needs to update into the windows. Because we do not want to wait the minutes required for an actual intersection, the cars in this traffic intersection travel much faster than “real” cars. In other words, you are encouraged to adjust the time delays so that the operation of your machine is convenient for you to debug Part a: 1. First you will run the Keil Project file. This lab starter project includes the template for all the functions that you will write. The comments describe the desired operation of that function. 2. Decide which port pins you will use for the inputs and outputs. Avoid the pins with hardware already connected. Run the starter code in the simulator to see which ports are available for the lights and switches; these choices are listed in Tables 1. The “don’t walk” and “walk” lights must be PF1 and PF3 respectively, but where to attach the others have some flexibility. Table 1 shows you three possibilities for how you can connect the six LEDs that form goN 30 100001 00,10 01,11 waitN 5 100010 goE 30 001100 waitE 5 010100 00,01, 10,11 10,11 00,01 00,01,10,11 goN 30 100001 X0 X1 waitN 5 100010 goE 30 001100 waitE 5 010100 XX 1X 0X XX the traffic lights and three possibilities for how you can connect the three positive logic switches that constitute the input sensors. Table 1: Possible ports to interface lights and sensors. Red east/west PB5 Yellow east/west PB4 Green east/west PB3 Red north/south PB2 Yellow north/south PB1 Green north/south PB0 Walk sensor PE2 North/south sensor PE1 East/west sensor PE0 Note: You might have to make hardware changes if you are using ports other than the ones that are listed above. Also, make sure to use the correct resistor values for the LEDs and switches. Part b: 1. Design a finite state machine that implements a good traffic light system. Draw a graphical picture of your finite state machine showing the various states, inputs, outputs, wait times and transitions. 2. Write and debug the C code that implements the traffic light control system. During the debugging phase with the simulator, use the logic analyzer to visualize the input/output behavior of your system. 3. After you have debugged your system in simulation mode, you will implement it on the real board. Use the same ports you used during simulation. The first step is to interface three push button switches for the sensors. You should implement positive logic switches. Please do not place or remove wires on the protoboard while the power is on. 4. The next step is to build the six LED output circuits. Build the system physically in a shape that matches a traffic intersection. You will use the PF3- 2-1 LED interface for the walk light (green for walk and red for don’t walk). Write a simple main program to test the LED interface)