Meggy Jr Simple and AVR
Plan for today:
–  ATmega328p chip
–  AVR assembly
CS453 Lecture
Meggy Jr Simple and AVR
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Example Meggy Java program
/**!
* PA2twodots!
* Lights up two pixels: (col 1,row 2):red (3,4) :white!
* MMS, 2/5/13!
*/!
import meggy.Meggy;!
class PA2twodots {!
public static void main(String[] whatever){!
Meggy.setPixel( (byte)1, (byte)2, Meggy.Color.RED );!
Meggy.setPixel( (byte)3, (byte)4, Meggy.Color.WHITE );!
}!
}!
 
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Meggy Java
Three ways to execute a Meggy Java program:
(1) Java-only using the meggy package that contains the Meggy class and
interface.
javac TestProg.java
java TestProg
(2) Compile to .s
this is what you are building in this class, then:
(2.1) Simulate AVR assembly code with MJSIM
java -jar MJSIM.jar // for GUI
java -jar MJSIM.jar -b -f ExampleFile.java.s // for command line
(2.2) Create executable from .s, download on device, run on device.
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Java-Only Meggy Java
 
 
 
meggy package
à go look at Meggy interface
arg_opts input file
–  format
int
bool
(button* delay)*
- What kind of grammar describes arg_opts?
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Using MJSIM
 
 
 
 
 
Authors
–  Ryan Moore did the initial design and prototype
–  Michelle Strout made it work with the assignments in 453
–  Cassie Helms added the emulator
–  Laura Adams added the feature where it takes pictures of state
Also uses an arg_opts file if one is available.
Keep in mind that the simulator does not cover all of AVR assembly.
Execute MJSIM.jar (java –jar MJSIM.jar) and find (via help) the
List of supported instructions.
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avr-gcc tool chain
 
 
 
 
See Resources page:
Building programs for the Meggy
and
Guide for Programming with Arduino and MeggyJrSimple interface
Also, read the meggy library code and .h file
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Meggy Jr Simple Library
 
Key concepts
–  LED screen (pixels)
–  Auxiliary LEDs
–  Buttons
–  Speaker
–  Check the AVR-G++ generated code for library calls, and their calling
sequence. AVR-G++ (and also MeggyJava) links in run time libraries:
–  Meggy Jr Library provided an interface to set and read values in the
Display Memory
–  Meggy Jr Simple lies on top of Meggy Jr library, and provides a higher
level API with names for e.g. colors
–  Michelle Strout and students (honors projects / theses) added some
functionality to the Meggy Jr Simple library
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Meggy Jr Simple Library functions
 
 
 
 
 
 
 
 
 
 
 
 
 
 
ClearSlate()
-- erase the whole slate
DrawPx(x,y,color)
-- set pixel (x,y) to color
DisplaySlate()
-- copy slate to LED Display Memory
SetAuxLEDS(value)
-- 8 LEDS above screen numbered 1, 2,4,..,128 (left to right)
value is a byte encoding in binary which LEDs are set
SETAuxLEDS(53) sets LEDS 1,4,16, and 32
ReadPx(x,y)
-- returns byte value of pixel (x,y)
CheckButtonsDown()
-- sets 6 variables: Button_(A|B|Up|Down|Left|Right)
GetButtons() returns a byte (B,A,Up,Down,Left.Right: 1,2,4,8,16,32)
ToneStart(divisor, duration)
-- starts a tone of frequency 8 Mhz/divisor for ~duration milliseconds
There are predefined tones.
Check out MeggyJrSimple.h
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Mapping Meggy Java Interface to Meggy Simple Interface
 
 
Let’s run the MJSIMulator to see an example of how this works:
PA2bluedot: Short (no stack code) version (from gcc compiler)
 
 
(We will look at the supplied code after we studied the assembly
language, in the next lecture.)
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