Lab 2, CMPET 211 – Introduction to Digilent Orbit Booster Pack
SUM 15, ADH
Lab Summary
This lab will introduce the use of the Digilent Orbit Booster Pack, which is a daughter card to be with the
Tiva LaunchPad Microcontroller. This lab will reinforce the concept of enabling ports and setting I/O
pins, and will provide opportunities for writing C code, understanding what the C code is doing, and
debugging the C code. There is an open ended component of the lab which will be used for grading
through demonstration of various LED controls through switches and push buttons.
Learning Objectives
1. Students will become familiar with the Digilent Orbit Booster Pack used to expand capabilities of
the Tiva LaunchPad microcontroller
2. Students will continue to work with and increase familiarity with the CCS IDE, the C
programming language (with the introduction of conditional If-Else statements and While
loops), and TivaWare library functions.
Lab Materials and Software
Students will need a Digilent Orbit Booster Pack daughter card, a Tiva TM4C123GXL LaunchPad
microcontroller by Texas Instruments, the supplied USB cable and access to Tiva TM4C123 software. The
hardware will be provided by the instructor in Week 3. Students should have their own LaunchPad by
week 4 (Lab 3).
Students need access to CCS, TivaWare, and LMFlashProgrammer software.
Setting up the Hardware and Launching the Software
Connecting the Tiva LaunchPad
1. Very carefully connect the USB cable to the microcontroller USB port labeled “Debug” (Note:
there are two USB ports, the correct one has a small microprocessor board next to it). It is
labeled “Debug” and it is NOT labeled “Device.”
a. PLEASE be VERY careful when inserting the USB cable – the female connection is VERY
fragile. It is a good idea to hold the female USB connector firmly in place while inserting
the cable. Do not twist the USB connections, just insert straight in.
2. Ensure the switch next to the on-board USB port is set to “DEBUG” and not “DEVICE”.
3. Connect the other side of the USB cable to an available USB port on the PC.
Connecting the Digilent Orbit Booster Pack to the Tiva Launchpad
To connect the Orbit Booster Pack, connect the Orbit’s female headers to the Launchpad’s male
headers. IMPORTANT: make sure the text “Orbit BoosterPack” is in the same orientation as the “Tiva
LaunchPad” text. See Figure 1.
Figure 1. ARM and ORBIT Combination. Note that the text at the bottom of each board is in the same orientation.
The Digilent Orbit Booster Pack is similar to a “shield” for Arduino hobby MCUs. The Orbit Booster Pack
is equipped with an accelerometer, temperature sensor, several LEDs, push buttons, switches, a
potentiometer, and an OLED screen. Today we will use the Orbit Booster Pack to further explore setting
up I/O pins and controlling LEDs with Switches and pushbuttons.
Launching CCS
1. In Lab 1 you created a “workspace” folder called “CMPET 211 Labs” on your USB or pass space.
Make sure this folder exists, or recreate it (IMPORTANT NOTE: if you recreate the folder, you
NEED to also download Lab 1 from the website, and copy it into this folder—it contains
additional support files needed today for Lab 2).
2. Use the internet to browse to http://sites.psu.edu/hilshey/classes/cmpet211/labs/ and
download the CMPET 211 Lab 2 zipped folder.
3. Copy the contents of the Lab 2 zipped folder into your workspace folder (see step 1) DO NOT
CREATE A SECOND “Lab 2” folder!
4. Launch Code Composer Studio (the shortcut looks like a grey 3x3x3 matrix cube)
5. Set the workspace to the folder described in step 1 (Figure 2).
Figure 2: Setting the CCS workspace.
6. The file “main.c” from last week may open within the CCS IDE. In the project tree, drill in to “Lab
2 CMPET 211” folder, and click on “main.c” to open the new lab 2 source code.
Note 1: if you don’t have a project tree, try two things. First click on the “CCS edit” icon at the
top right side of the CCS window. If this doesn’t work, select the following using the drop down
menus: WindowReset Perspective…
Note 2: If you don’t see Lab 2, click ProjectImport CCS Projects. Browse to the Lab 2 project
folder, select it, and click finished.
7. Your CCS window should look similar to Figure 3 (you may have some different project folders
compared to the figure, but you will have “Lab 2 CMPET 211”).
Figure 3: The CCS IDE with Lab 2 source code open
Doing the Lab, Writing the Code
This lab is designed so that the you will type a good amount of C code. Although, you will not be writing
your “own” code yet, there is value in retyping prewritten code. This forces you to look at the prewritten
code more carefully which may probe you to ask yourself, “what does this line do?” Additionally, there is
a benefit in typing lots of code, in that you are bound to make a few typos. Typos are great
opportunities to learn debugging; typos aren’t necessarily a bad thing when we’re learning! Only by
typing the code and then debugging the errors will a user really understand how to do projects.
Note: You will start typing code after Figure 6 below. The sections and figures will describe the functions
of the prewritten, provided code.
Side Note: Pair Programming
You are likely working with a partner or even two. While one writes code, what does the other do? This
is an opportunity to apply “Pair Programming.” Here are some salient points taken from Seattle
Consultant David Bernstein’s software development blog (tobeagile.com) post “Seven Strategies for Pair
Programming”:
Engage Driver and Navigator: Pairing is not about taking turns doing the work. Each
member of the pair has specific duties, working together, and in parallel. Both the
person at the keyboard (driver) and the one looking over their shoulder (navigator)
are actively engaged while pairing.
Swap roles frequently: Taking turns driving and navigating every 20-60 minutes
helps keep collaboration at a maximum. “Handing off the keyboard” also helps
propagate knowledge across the pair and ultimately, by pairing with other team
members, propagates knowledge throughout the team.
Many hyper-productive teams I know pair all of the time. Don’t believe that pairing
cuts productivity in half, which would only be true if the limiting factor in software
development is typing. When done correctly, pairing can significantly increase the
throughput of value created while slashing defects. I know of no other approach to
software development that can radiate knowledge and skills throughout a team more
rapidly than pairing.
Writing and understanding the code
Figure 4 displays the provided header files. Recall from Lab 1 that Header files contain all functions you
may need to create a project. When using our Tiva LaunchPads, always include these 9 header files.
Remember that inclusion of all these lines of code doesn’t necessarily mean that all the code will be part
of the machine code. The header files contain all the “possible” functions that will be necessary. When
the compiler actually accomplishes the work, it will only include the functions that are required.
Figure 4: Header Files to be used with Tiva LaunchPad
The next section of provided code (similar to Lab 1) will set up the internal clock (here used to create
time delays) and will then set up our Input/Output (I/O) pins. Recall that we first enable ports (each port
has a collection of I/O pins) which is similar to “powering them up.” Then we define the pins we want to
use as either outputs or inputs. See Figure 5.
Interesting note on setting up I/O: The ARM processor is ultimately designed to be highly
efficient and to be able to operate for months at a time on batteries. To accomplish this, the
device is virtually powered down when it is turned on. The device has a series of ports that then
connect to external devices such as UARTs and I2C busses (discussed in future labs/lectures).
EVERY TIME a new project is started, the first thing than must be done is to first enable the ports
and then set up the pins. Unused ports are never powered; this is how we save energy!
Figure 5. Enabling Ports and Configuring Pins
As shown in Figure 5, the first port to be enabled is port C (GPIOC). Once the port is enabled, the next
step is to configure the pins. In this case, pins 6 and 7 are enabled as output pins. As another example,
the bottom line, Port A, Pin 6, is configured as an input pin which will take input readings from Switch 2
on the Orbit Booster Pack. Review Appendix 1 to see which ports house the pins that are tied to the
devices we are using.
The next lines will declare variables (tells the compiler to create a variable) and then will define them
(stores the desired value in the variable). See Figure 6.
Figure 6: Declaring and defining a variable
Following the variable declaration and definition, you will see a conditional “while” loop in your
provided code (the full contents of this loop is not yet written). The while loop will perform its contents
(i.e. reading inputs and setting outputs) indefinitely because its condition is set to “1,” which is always
true (0 is false, everything else is true, including 1). Nested within the while loop is an If-Else conditional
statement and another embedded conditional while loop.
The “If” conditional statement “listens for the switch.” When the I/O pin tied to the Orbit Switch 2 reads
high (e.g. when Port A, Pin 6 is high), it will perform the commands within the “if” statement. Otherwise
if the I/O pin reads low, the “else” conditional statement is executed.
The “while” conditional statement (embedded within the first while loop) will be executed if the Orbit
Push Button 1 is depressed (i.e. while the pin tied to the push button reads high, execute the commands
within the while loop).
Now it’s time to write code. Fill in the commands for the If-Else and While statements as shown in Figure
7 and 8. Use Pair Programming technique such that one student types and the other verifies that the
typing is correct. Pay attention to case sensitivity. Switch roles at each conditional statement (i.e. one
does the “if,” one does the “else,” etc.).
Deliverable Question as Part of Graded Demonstration
Later, during demonstration of your work, you may be asked to explain what is happening in any of the
GPIOPinWrite or GPIOPinRead lines of code shown in figures 7 and 8. You will need to be able to explain
why every part of that line is present. These lines of code (or ones just like them) were described in Lab
1.
HOT TIP: A phenomenal resource for learning more about any of the common Tiva commands is the
TiveWare™ Peripheral Driver Library User’s Guide, which can be found by navigating to
C:\ti\TivaWare_C_Series-2.1.1.71\docs and selecting “SW-TM4C-DRL-UG-2.1.1.71” or googling the
above document title. Use “control f” to search for the commands you want to know more about. This
resource (among others) is also available on Hilshey’s website under the “useful downloads” page.
Figure 2. The "IF" Work
Figure 3. While Loop for Blinking Lights
As shown in Figure 8, if the button is pushed, we write outputs to all the LEDs First we write 1s and
then after a little delay time we write 0s. This is repeated until the button is released.
Now it is possible to compile the program, create the executable, and run the program.
On the tool bar, directly under the “Project” drop down menu, locate and click the “debug” icon (it looks
like a green beetle -- see Figure 9). Do not click the drop down arrow next to the debug icon, just click
the beetle. This causes the main.c source code to compile and then to be burned onto the
microcontroller ROM. If you get errors, skip to the next page.
Figure 9: Compiling code and opening the debugger.
There are now several options. The designer can step line by line through the program by clicking on
the yellow “step over” icon (it is arrow shaped). When ready to continuously run the program, click on
the green arrow “resume” icon (see figure 10) in the Debug pane.
Figure 10: Running the code on the microcontroller.
Click on the red square “stop” icon to return to the text editor.
If your code is correct, when Switch 2 is in the Up position, the Orbit LEDs will flash from right to left and
the LaunchPad LED will be blue (from the “If” statement). The Orbit LEDs change directions and the
LaunchPad LED turns green when the Switch 2 is in the Down Position (from the “Else” statement). All
LEDs flash when Orbit Pushbutton 1 is held down (from the “while” statement).
HOT DEBUGGING TIPS: if you have “bugs” from typos, common errors stem from: 1.)
unbalanced parenthesis or brackets; 2.) missing semi-colons at the end of commands; 3.)
misspelled function or variable names; and 4.) incorrect letter case – C is case sensitive.
An error icon (red circle with an “x”) will usually show up at the line with the error for
misspellings or case errors. The error icon shows up at the command FOLLOWING a missing
semi-colon, parenthesis, or bracket (so, look up!). Debugging gets easier with experience, but is
not usually easy in the beginning! Refuse to get frustrated!
Change the Code, Learn Through Doing
Now is your opportunity to experiment. Start slowly and build up. You may want to make a copy of the
“Lab 2 CMPET 211” folder in the “project explorer” tree. Don’t just copy “main.c” – copy the whole
project folder to save headaches! This way you can preserve the original file and make changes in the
copied file.
Challenges:
1.) Remove the if/else statement, see results (you do not need to demonstrate this)
2.) Change from button 1 to button 2*
3.) Take your SOS code from Lab 1 (if you got that far – if not, make something similar now) and
embed it into the Lab 2 with another “while” tied to Switch 1.* Keep the rest of the Lab 2 code
the same.
*When using the other switch or push button, you will need to refer to the LaunchPad Evaluation Board
and the Orbit Schematics. There is a quick cheat sheet at the end of this tutorial that will provide ports
and pins. Remember: Enable Ports, Set Pins.
Demonstration/Grading
To receive full credit, you must demonstrate at least Challenge 2 in the previous section. You may also
be required to explain one or more lines of code. When you are ready to demonstrate, contact your
instructor. This Lab should be demonstrated before leaving today.
There will be no hard copy deliverables due for this lab. This lab is worth 50% of a standard lab (due to
no hardcopy deliverables).
If you choose to leave early, you must demonstrate challenge 2 and 3 to receive full credit.
Appendix 1: Block Diagram of the Pins Used in Projects