Description
Preparation:
You will need a LaunchPad, one to three push buttons (not switches! Ask instructor for buttons
if needed. Number required depends on number of on LaunchPad buttons used), one to three
10kΩ resistors, eight color LEDs (2 red, 4 yellow, and 2 green), and eight resistors for the LEDs
(between 330Ω to 1kΩ each).
Book Reading: Textbook Sections 2.7, 4.2, 6.5, 9.4, 9.5, 9.6
Starter Project: Lab5/Project 1
Purpose:
The purpose of this project is to combine the concepts of
• interfacing to switches and LEDs,
• using a Moore finite state machine (FSM), and
• using interrupts (GPIO and SysTick).
You will perform explicit measurements on the circuits to verify they are operational and to
improve your understanding of how they work.
System Requirements:
Design a system based on a drag race. A ‘Christmas Tree’ is the light signal that drivers use to
determine when to accelerate (ie start the race), which is simulated by our LEDs. A track has
multiple sensors to determine if a car is in the proper position (“staged”), simulated by pressing
our “lane sensor” buttons, one per lane (left lane and right lane). Our project will determine the
winner based on who releases their button fastest after the green LEDs are lit. A reset button will
be used to override the state machine current state and reset the board back to the initial state
(similar to the reset button on the LaunchPad).
Consider a drag strip shown in Figure 1. There are two lanes (Left and Right), with a “Christmas
tree” showing LEDs for both lanes.
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There are three inputs to your LaunchPad:
• Reset – board immediately goes to Initialize state regardless of current state and SysTick
timer value
• Left lane sensor – Represents if car in left lane is in proper position to start race
• Right lane sensor – Represents if car in right lane is in proper position to start race
Logic:
• The system starts in the Initialize state, during which all LEDs are lit. This state must (re)start
the SysTick timer. After 1 second, the system unconditionally transitions into Wait for Staging
state, where no LEDs are lit.
• While in the Wait for Staging state, it checks every 0.5 seconds if both left lane is staged(left
lane button pressed) and right lane is staged (right lane button pressed). If both are pressed,
the system transitions to the Countdown Y1 state. Otherwise the system stays in the Wait for
Staging state.
• In the Countdown Y1 state, only LEDs Y1L and Y1R are lit. After 0.5 seconds, if the left lane
button or right lane button is released (or both), the system goes into the False Start
Left/Right/Both state (those are 3 different states). Otherwise the system transitions to the
Countdown Y2 state.
• In the Countdown Y2 state, only LEDs Y2L and Y2R are lit. After 0.5 seconds, if the left lane
button or right lane button is released (or both), the system goes into the False Start
Left/Right/Both state (those are 3 different states). Otherwise the system transitions to the
Go state.
• In the Go state, only LEDs GL and GR are lit. Every 0.05 seconds, the system checks if thelane
buttons are pressed. If only left lane button is released, the system transitions to WinLeft. If
only right lane button is released, the system transitions to Win Right. If both lanebuttons are
released, the system transitions to Win Both.
• In the False Start Left state, only LED RL is lit. In the False Start Right state, only LED RR islit. In
the False Start Both state, only LEDs RR and RL are lit. From any of these 3 states, the system
transitions to the Wait for Staging state after 1 second.
• In the Win Left state, only LED GL is lit. In the Win Right state, only LED GR is lit. In the Win
Both states, only LEDs GR and GL are lit. From any of these 3 states, the system transitions to
the Wait for Staging state after 1 second.
• While the reset button is pressed, immediately (without waiting for state SysTick timer to
change) stop the SysTick timer and transition to the Initialize state. You do not need to
consider the reset button as an input to your state machine. So, there are only 2 inputsto
your state machine: left lane sensor and right lane sensor.
Implementation Requirements:
• A two-button interface using positive or negative logic (or combination of both) and eitheron
board buttons or on breadboard buttons, for the left lane and right lane sensor buttons. Use
GPIO interrupts with priority 2 to detect both edges for both sensors.
• An eight LED interface that implements either positive or negative logic (or combination of
both) using on breadboard (not on LaunchPad) LEDs
• A one button interface on a separate port than the left and right lane sensor buttons to
represent the reset button. Use GPIO interrupts with priority 1 to detect level sensitive
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(when pressed) for reset button.
Implement a Moore finite state machine (FSM). There should be a 1-1 mapping between
the FSM graph and data structure. For a Moore FSM, this means each state in the graph has
a name, an output, a time to wait, and 4 next state links (2 inputs, so 22 = 4 combinations of
inputs). The data structure has exactly these components: a name, an output, a time to wait,
and 4 next state pointers (22 = 4 combinations of inputs). There is no more and no less
information in the data structure than the information in the state graph. There should be
onlya single output variable; use bit masking and bit shifting if you need to separate
values.
There can be no conditional branches in the program. This will make debugging the FSM
engine trivial.
You must use SysTick interrupt with Priority 3 to implement state delays.
The state graph should define exactly what the system does in a clear and unambiguous
fashion. In other words, do not embed functionality (e.g., flash 3 times) into the software that is
not explicitly defined in the state graph.
Each state has the same format. This means every state has exact one name, one output field,
one time to wait, and 4 next indices.
Use good names and labels (easy to understand and easy to change). Examples of bad state
names are S0 and S1.
Procedure:
1. Decide which port and pins you will use for the inputs and outputs. Avoid the pins with
hardware already connected.
2. Define bit-specific addresses for input and output, one per direction (input/output) per port
used.
a. Your Input variable must have the 2 switches mapped to the 2 least significant bits.
Perform right shifts (>>) and any other operations needed to make the bits that way.
Imaginary example:
Input = SENSOR_PORTA >> 2 + SENSOR_PORTF >> 1; // read sensors and shift bits
b. You may also need to ‘split’ your OUTPUT variable to go to the different output ports.
Imaginary example:
LIGHT_PORTB = FSM[S].Out & 0x3F; // set lights port b
LIGHT_PORTF = (FSM[S].Out & 0x0A00) >> 8; // set lights port f
3. Design a Moore finite state machine that implements the system described. Draw a
graphical picture of your FSM showing the various states, inputs, outputs, wait times and
transitions, as well as a state table for the FSM.
4. Write and debug the C code that implements your system.
a. Your GPIO interrupt handlers should update global variable(s) based on the GPIO.
b. Your SysTick handler should:
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i. Determine the new current state based on the global variables set by the GPIO
interrupt handlers and the current state,
ii. Set the system outputs (LEDs) based on the new current state,
iii. Configure the SysTick delay to be the delay needed for the new current state.
5. Implement your system on the real board. Use the same ports you used during simulation.
Do not place or remove wires on the protoboard while the power is on. Build and test the
switch circuits.
Figure 2 Switch and LED interfaces on the Stellaris® LaunchPad Evaluation Board.
Deliverable:
1) Demonstrate your lab. Label the physical board using e.g. post its, cut up index cards, etc
so that each LED and switch has an obvious name/label before demonstrating.
a. In simulator
b. On board
2) Submit a project report (eg Word Document) to the Beachboard Dropbox containing:
a. Class name, lab number and name, your name and your partner’s name (if applicable)
b. Table showing list of GPIO ports + pins used (similar in format to “Recommended GPIO
Pins” in Project 1 description)
c. Description of which bits in the input map to which GPIO ports + pins.
d. Description of which bits in the output map to which GPIO ports + pins.
e. State table for your Moore FSM
f. State diagram for your Moore FSM
g. Photographs of your hardware system: One per state.
h. Labeled photograph of your hardware system with all LEDs and buttons labeled. (Can be
a same picture as above.)
i. Diagram of your hardware system (see Figure 2 for an example)
j. Software source code: The .c file
k. Include short description (for example, a couple sentences) describing the extra credit
changes you made.
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Code Setup:
Recommended starting point is Lab5 or Project 1.
Additional References (Optional):
• https://en.wikipedia.org/wiki/Christmas_tree_(drag_racing)
• https://startdragracing.com/drag-racing-christmas-tree
