Lab 1 – Introduction to AVR Development Tools

Lab 1 – Introduction to AVR Development Tools ECE 375
ECE 375: Computer Organization and
Assembly Language Programming
Lab 1 – Introduction to AVR Development Tools
SECTION OVERVIEW
Complete the following objectives:
• Connect your AVR microcontroller board to a TekBot (optional).
• Create a new Atmel Studio project.
• Download and compile the sample AVR assembly source code given on the
lab webpage (BasicBumpBot.asm).
• Understand how to connect and operate the USBASP AVR programmer.
• Upload the previously-compiled sample program to the flash memory of the
TekBots AVR microcontroller board (mega128), and observe it running.
PRELAB
You will be required to complete a prelab assignment before attending the lab
session itself. These prelabs will cover the important concepts and background
knowledge necessary to accomplish each corresponding lab.
Prelab assignments are due before the beginning of your lab session each week.
If you have not submitted your prelab by the starting time of the lab session, you
will receive no credit for that prelab. For general information about assignment
submission policies, please refer to the syllabus on the lab webpage.
For this first lab, there is no prelab assignment.
PROCEDURE
Wiring Your TekBot
1. Use of the TekBot is optional for the ECE 375 lab. If you choose
to use your TekBot, use the following instructions to ensure it is properly
wired to the mega128 board. Otherwise, skip ahead to the next subsection,
entitled “Compiling an AVR Assembly Program”.
Connection Port Pin Alternate Function
Right Whisker D 0 External Interrupt 0
Left Whisker D 1 External Interrupt 1
Right Motor Enable B 4 PWM Output for TCNT0
Right Motor Direction B 5 PWM Output A for TCNT1
Left Motor Direction B 6 PWM Output B for TCNT1
Left Motor Enable B 7 PWM Output for TCNT2
Table 1: mega128 Port Usage for TekBot Connection
2. Table 1 shows which port pins of the mega128 board must be connected to
the TekBot.
To make the wires needed to connect your mega128 board to your TekBot,
you can use the ribbon cable that came with your original TekBot kit, solder
male headers to the ends, and add a bit of heat shrink tubing onto each
connection. If you are not familiar with this technique, there is a short
tutorial on the TekBots webpage that explains this process in detail.
Since we are working with a modular programmable AVR microcontroller
board, you could connect the whisker inputs and motor controller outputs
to any pins on any port on the board. But, for this lab and future labs to
work properly, these specific wires need to be connected in a certain way.
Please follow the convention specified in Table 1 and maintain this wiring
throughout the course, so that your use of some alternate pin functions in
later labs behaves as expected.
3. When you have completed the wiring, be sure to double-check all connections
before you turn the power on. If you have wired things incorrectly (especially
if you have switched Vcc and ground), you can easily destroy parts of your
TekBot. If you aren’t confident in the correctness of your wiring, please ask
a fellow student, your TA, or the TekBots store to double-check your work.
Compiling an AVR Assembly Program
1. Download the sample code (BasicBumpBot.asm) available on the lab webpage. This is a simple AVR assembly program that is well-commented and
ready to compile. All code that you produce for this course should be as
well-commented as this code. Save this code somewhere you can find it.
2. Atmel Studio is the Integrated Development Environment (IDE) that you
will be using to develop your AVR assembly code throughout this course
(with the exception of Lab 2, which uses C). Atmel Studio is a powerful
©2021 Oregon State University Winter 2021 Page 1
Lab 1 – Introduction to AVR Development Tools ECE 375
IDE created by Atmel for their line of AVR microcontrollers. You will be
using it to write assembly programs for your AVR microcontroller board
(mega128), which uses an ATmega128 microcontroller. Section 2 of the
AVR Starter Guide, which can be found on the lab website, contains a good
overview on how to use the IDE, as well as some step-by-step tutorials.
Briefly read through this section to gain a basic understanding of the Atmel
Studio workflow.
Atmel Studio is already installed on the computers in the lab classroom. If
you plan to use your personal Windows computer for some or all of your lab
work, the latest version of Atmel Studio is available for download on Atmel’s
website. It is also possible to use your personal Mac OS X or Linux computer
for AVR assembly programming, but you will need to find an alternative to
Atmel Studio on your own. Also, a few of the labs in this class rely heavily
on the use of Atmel Studio’s built-in AVR simulator, so please keep in mind
that occasionally you may be relegated to completing your work on one of
the lab computers instead of your personal device.
3. Once you have finished browsing through Section 2 of the AVR Starter
Guide, follow the specific steps in Section 2.1.2 to create a new project.
In most IDE tools, a project is the base starting area to your program. It
consists of all files you use and any settings for the program. In this case, the
file you’ll want to include is the AVR assembly sample program, which you
downloaded from the lab website earlier. Continue following the instructions
in Section 2.1.2 to associate the sample program with the project you just
created.
4. Now that you have loaded the sample program into your Atmel Studio
project, take a moment to look over the sample code. Although you haven’t
seen any AVR assembly code in this class yet, read the comments and see if
you can follow the general structure and flow of the program. For reference,
the general operation of the program is described in Figure 1.
5. Using the project you created, continue on to Section 2.1.3, and perform
steps 1 and 2 to compile the sample program (you can disregard the simulation instructions in this section, as this topic will be covered in a later lab).
Note: When an AVR assembly program is compiled, the resulting output
is a binary program file (called a HEX file, with a .hex extension). This
HEX file contains the actual binary instructions that will be executed by
the ATmega128 microcontroller.
You now know how to create a new AVR project in Atmel Studio, include an
• Initializes key components of the ATmega128
• Starts the TekBot moving forward
• Polls the whiskers for input
• If right whisker is hit
– Backs up for a second
– Turns left for a second
– Continues Forward
• If left whisker is hit
– Backs up for a second
– Turns right for a second
– Continues Forward
Figure 1: Theory of Operation for Lab 1 AVR Assembly Code
assembly program into that project, and then compile the program into usable
program code. Next, you will learn how to upload the compiled program to the
microcontroller and watch it run.
Uploading a Compiled AVR Program
1. Use the Windows application Universal GUI.exe (already installed on the
lab computers, and available for download on the lab webpage) to upload the
compiled .hex file to the flash memory of the ATmega128 microcontroller.
(For detailed instructions, follow the steps given in the Universal GUI User
Guide linked on the lab webpage.)
2. With the HEX file uploaded to the microcontroller, you can observe the
behavior of the sample program (if using a TekBot, unplug it from the
computer and turn it on). The LEDs on the mega128 board should indicate
that the board is performing a basic BumpBot routine (remember, Figure 1
gives a description of the full routine). To receive your implementation
points for this lab, demonstrate to your TA that your board is performing
this correct BumpBot behavior.
©2021 Oregon State University Winter 2021 Page 2
Lab 1 – Introduction to AVR Development Tools ECE 375
STUDY QUESTIONS / REPORT
For every lab, you will be required to submit a write-up that details what you
did and why. As a requirement of Lab 1, you do not need to complete a full
lab report. Instead, you need to answer the study questions given later in this
document. Provide your answers using the “Additional Questions” section of the
lab template. You must use one of the templates (.doc or .tex) provided
on the lab webpage.
When putting together each lab’s write-up, you will utilize the template file
to structure your report. Include enough detail so that another student could
recreate the lab by using your write-up as a guide. See the lab webpage and
template for specific details on what should be included in the lab write-up. You
must submit your write-up and code via Canvas by the start of the following
lab. NO LATE WORK IS ACCEPTED.
You are responsible for turning in a clean, organized, and professional document free of misspelled words. The code you turn in must include sufficient
comments, such that ANOTHER STUDENT could reasonably be able to understand your code. Code that is not well-documented will result in a severe loss
of points for the write-up portion of your lab grade. For an example of the style
and detail expected of your comments, look at the code you just downloaded.
Generally you should have a comment for every line of code.
Study Questions
Most of the labs you do in this class will have study questions that are to be
answered within your lab write-up. This lab’s study questions are given below,
and will be due at the start of lab next week. As is often the case in engineering courses, there will be some occasions when you are exposed to information
that has not been covered in class. In these situations you will need to get into
the habit of being proactive and using your study skills to research the answers.
This can involve strategies such as reading ahead in the textbook, checking the
datasheet, searching online, or reviewing other documentation from the manufacturer.
1. Go to the lab webpage and download the template write-up. Read it thoroughly and get familiar with the expected format. What specific font is
used for source code, and at what size? From here on, when you include your source code in your lab write-up, you must adhere to the specified
font type and size.
2. Go to the lab webpage and read the Syllabus section carefully. Expected
format and naming convention are very important for submission. If you
do not follow naming conventions and formats, you will lose some points.
What is the naming convention for source code (asm)?
3. Take a look at the code you downloaded for today’s lab. Notice the lines that
begin with .def and .equ followed by some type of expression. These are
known as pre-compiler directives. Define pre-compiler directive. What
is the difference between the .def and .equ directives? (HINT: see Section
5.1 of the AVR Starter Guide).
4. Take another look at the code you downloaded for today’s lab. Read the
comment that describes the macro definitions. From that explanation, determine the 8-bit binary value that each of the following expressions evaluates
to. Note: the numbers below are decimal values.
(a) (1 << 5)
(b) (4 << 4)
(c) (8 >> 1)
(d) (5 << 0)
(e) (8 >> 2|1 << 6)
5. Go to the lab webpage and read the AVR Instruction Set Manual. Based
on this manual, describe the instructions listed below.
ADIW, BCLR, BRCC, BRGE, COM, EOR, LSL, LSR, NEG, OR, ORI,
ROL, ROR, SBC, SBIW, and SUB.
CHALLENGE
Challenge problems are additional tasks that can be performed for several of
the labs. By successfully completing a particular lab’s challenge problem, you
can get extra credit for that lab. To get credit for a challenge problem, you
must successfully demonstrate it to your TA, as well as document it in your lab
write-up. This lab’s challenge problem is given below:
• You have learned to use a simple tool to download a sample program into
your mega128 board. Modify the sample program so the TekBot will reverse for twice as long before turning away and resuming forward motion.
Demonstrate this to your TA, and include a copy of your modified assembly
program when you submit your answers to the study questions.
©2021 Oregon State University Winter 2021 Page 3