Lab 2: AVR Programming

Assigned: Tuesday, June 28

The goal of this lab is to become familiar with the ins and outs of programming on the AVR mini.

0. Set up your environment to use the AVR

a. Copy the pre-prepared AVR and AVRlib files to your home directory by running the following script:

cd ~
/usr/ccrma/web/html/workshops/mid2005/setup

b. Make a directory for Lab 2 in your MID directory

cd ~
mkdir MID/lab2

c. Set up AVR connection to PC

Connect power cable, connect serial cable to right hand port, and power-up the AVRmini

d. Test AVR setup with "flash" test code

Make yourself a copy of the FLASH demo from avrlib-demos:

cd ~/MID/lab2
cp -r ~/avrlib-demos/flash .
cd 
flash

Compile and download the code to the AVRmini. Press the RESET button on the AVRmini and within 2 seconds type:

make 
load

You should see a sort of makeshift progress bar as a bunch of "#" characters print. If the program transferred successfully, then press RESET again. Connect the PBLED header to the PORTD header.

If everything is working, a LED on the AVRmini board should start flashing.

1. AVRMini Input/Output

a. Review architecture and programming, as necessary

• About Microcontrollers
• C programming for the AVR

b. Momentary pushbutton

• Compile and load BUTTON from the avrlib-demos to your Lab 2 folder:

  cd ~/MID/lab2
  cp -r ~/avrlib-demos/button . 
  cd button 
  make 
  load

• This requires using PORT B instead of D. (Connect the PBLED header to the PORTB header.)
• When you press SW4 ("Switch number 4"), LED0 ("Light Emitting Diode number 0") should light
• Look at the code in an editor:

  nedit button.c 

  In particular, note that there's a comment near the top of the code that tells you

  //  USING THE AVRMINI 
  DEVELOPMENT BOARD, CONNECT
  //  THE LED/PUSHBUTTON JUMPER TO THE PORT B 
  JUMPER.
  

  All of the demo programs in avrlib-demos have a comments like this.

Optional: Toggle pushbutton using debounce.

• Compile and load TOGGLE from the avrlib-demos

  cd ~/MID/lab2
  cp -r ~/avrlib-demos/toggle . 
  cd toggle
  make 
  load

• Look at the code in an editor. Compare button.c and toggle.c. Why is there a debounce mechanism in toggle.c but not in button.c? How does the debounce mechanism work?
• What happens if you change the debounce threshold to 1? (hint - try toggling the LED 10 times)
• What happens if you change the debounce threshold to 30000?
• Can you change it to 100000? (hint - you need to change something else, too. DO NOT SPEND MORE THAN 5 MINUTES TRYING TO FIGURE THIS OUT!)
• Especially optional section: instruction counting and timing
  • Really, we mean it, don't waste time on this unless it fascinates you
• Create the file button.ss by typing make button.ss
• Look at button.ss - these are the instructions that are actually written to the microprocessor.
• Look in the two sections <checkButton> and <main>. Each line corresponds to one instruction of the microprocessor. What debounce threshold value would give approximately 1 second of delay between the button press and the LED lighting up? (Hint: you will need to look at the Atmel Instruction Set documentation.)
• Why is using a very high debounce threshold a bad way to implement a 1 second delay? (There are at least three good reasons.)
• The best way to implement a 1 second delay is with the timer library in avrlib. Put the debounce threshold back to a reasonable value for debouncing and reintroduce the 1 second delay properly:
  • Add #include "timer.h" at the top of toggle.c
  • Add timerInit(); to the beginning of your main() procedure but after your varaible declariations..
  • Add a call to the timerPause() procedure in the right place in your program.
  • In your makefile, add $(AVRLIB)/timer.c to the list of files in the definition of SRC
  The new makefile line should look like this: SRC= $(TRG).c $(AVRLIB)/timer.c
• Find the maximum delay time before you can notice a pause between the button press and the LED illuminating.

c. Four buttons:

• Write a program to control 4 LEDs with 4 buttons. It's up to you to do some "interaction design": think of your own way for actions with the four buttons to control the states of the LEDs. Feel free to write this program from scratch, but we recommend that you start with the FOURTOGGLE demo.

d. Beep:

• Load BUTTONBEEP as you did BUTTON and FLASH above.
• Make sure the blue wire from your speaker is connected to pin D5 and the black wire from the speaker to ground.
• You should hear a beep when you press SW4.
• Try inserting a pause between turning on the LED and playing the beep. In case you didn't do part 3b, here are the step-by-step instructions for using the avrlib's timer facilities:
  • Add #include "timer.h" at the top of buttonbeep.c
  • Add timerInit(); to the beginning of your main() procedure.
  • Add a call to the timerPause() procedure in the right place in your program.
  • In your makefile, add $(AVRLIB)/timer.c to the list of files in the definition of SRC
• At what point does the delay become noticeable? What if the beep comes before the light?
• Try finding the largest unnoticeable delay time as in #3 using the beep as feedback. Is it different?

3. Compile, Run and Play the AVRsimon:

• Compile the code and program the AVR:

cd ~/MID/lab2
cp -r ~/avrlib-demos/avrsimon . 
cd avrsimon 
make load

• You should now be able to play the Simon game provided. Pay attention to things you like and dislike about the flow of the game and the interaction.
• Improve the game to make it more interesting and engaging. Here are some suggestions, but feel free to come up with others:
  • Keep stats - this is an easy addition involving adding two counters for correct and incorrect performance, and adding a way to start a new game without the reset button.
  • Add levels of play - make it get progressively more difficult (e.g., longer patterns, increasing tempo)
  • Make it more interactive - give the user more choices on the style of the game (e.g., select a level)
  • Add timing - Try to evaluate the user's rhythmic accuracy
  • Change the nature of the game somehow