Transcript Programming with Lejos, part 1

Programming with Lejos
Part 1
What is lejos?
• Cut-down version of Java for the RCX
platform
• Includes:
– Lejos API
– JVM
• API includes functionality needed to
control motors, sensors, buttons as well
as many components from the standard
Java API
How it works
• Lego firmware is replaced with lejos JVM
(only has to be done once)
• Program source code is written &
compiled on PC
• Compiled code (Java byte code) is
downloaded to & runs on RCX
JVM & RCX technical specifications
• RCX has 32k of RAM
– 4K unusable
– 16K for Lejos
– 12K free memory for user code!
• Built-in support for:
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Floating-point numbers (useful for trig/navigation)
Limited multithreading
2-dimensional Arrays
Limited recursion
Events & the lejos API
• Objects & their listeners:
– Timer: TimerListener
– Button: ButtonListener
– Sensor: SensorListener
• Object acts as event source; when event
occurs, all registered listeners we notified
& can execute appropriate code
Exception Handling & Garbage
Collection
• Lejos follows standard Java exceptionhandling model
• Lejos does NOT have automatic garbage
collection
– Important to re-use objects rather the just
creating new ones
– Forces good memory “hygiene”
Packages in the Lejos API
• josx.platfom.rcx: includes classes for controlling
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–
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3 output ports (A, B & C)
3 input ports (1, 2 & 3)
3 buttons (Prgm, Run, View)
LCD display
Speaker output
IR communication
• There are also classes for accessing system
time & monitoring battery power
Packages in the Lejos API
• java.lang: Includes some of the most
commonly used standard classes
– Math
– String
– StringBuffer: mutable version of String
– System
– Thread
– Throwable
Packages in the Lejos API
• java.util: like java.lang, includes some
familiar and/or useful classes
– Random
– Vector: dynamic array
– BitSet: series of bits
Packages in the Lejos API
• java.io: provides support for transmitting
data streams via the IR port
– Serializable interface
– InputStream, OutputStream,
DataInputStream, DataOutputStream and
IOException classes
Packages in the Lejos API
• josx.robotics: generic classes & methods
for robot-specific tasks
– Behavior Control classes: includes Behavior
interface & Arbitrator class
– Navigation classes
Classes in josx.platform.rcx
• Sound class contains a set of static methods
that can produce predefined or custom sounds:
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Sound.beep() // beeps once
Sound.twoBeeps() // beeps twice
Sound. buzz() // emits almost inaudible tone
Sound. beepSequence() // series of
// downward tones
– Sound. playTone (int frequency, int duration)
• MinSound class is a cut-down version - contains
only the (deprecated) playTone method
Classes in josx.platform.rcx
• Unlike most Java environments, robots running
Lejos are physical objects
• The RCX brick has 3 programmable buttons, 3
sensor connections and 3 power output ports
• When programming for the RCX, these
components are represented by predefined
static objects; it wouldn’t make sense to
instantiate more sensor ports, for example,
because physically there are just 3
Classes in josx.platform.rcx
• The LCD, MinLCD and TextLCD classes
relate to various aspects of the RCX’s
LCD display
• MinLCD, like MinSound, is a cut-down
version primarily used to conserve
memory
• LCD is used for number display, while
TextLCD can display Strings
LCD class methods (all are static)
• void refresh()
• void setNumber (int code, int value, int
point) - parameters:
– code: value Indicates use of signed or
unsigned number, use of 5th digit
– value: number to display
– point: code indicating position of decimal point
• These 2 methods are also found in
MinLCD
LCD class methods (all are static)
• void clear(): clears display
• void showNumber(int i): displays an
unsigned, up to 4-digit number
• void setSegment (int code): activates the
display segment indicated by code; codes
are defined by static constants in the
Segment interface
Example 1: Sounds & Display
import josx.platform.rcx.*;
public class MakeNoise {
public static void main(String[] args) throws InterruptedException {
int freq; // frequency of tone
for (freq = 440; freq < 10000; freq = 110 * freq / 100) {
// ascending tones
LCD.showNumber(freq);
Sound.playTone(freq, 50);
Thread.sleep(500);
}
for (freq = 440; freq > 20; freq = 90 * freq / 100) {
// descending tones
LCD.showNumber(freq);
Sound.playTone(freq, 50);
Thread.sleep(500);
}
}
}
Classes in josx.platform.rcx
• Button class methods include:
– public void addButtonListener (ButtonListener
b)
– public boolean isPressed()
– public static int readButtons()
• Returns int with bits set: 0x02 (view button pressed) 0x04
(prgm button pressed), 0x01 (run button pressed). If all
buttons are released, this method returns 0.
– void waitForPressAndRelease () throws
InterruptedException
• stops execution until button pressed & released
Classes in josx.platform.rcx
• Button class also contains static fields that
represent the RCX buttons:
– Button.PRGM
– Button.RUN
– Button.VIEW
• ButtonListener interface specifies 2
methods:
– public void buttonPressed (Button b)
– public void buttonReleased (Button b)
Classes in josx.platform.rcx
• ROM class: provides access to embedded
routines in the RCX ROM; includes static
method int getBatteryPower()
• Motor class: includes methods controlling
DC output to ports A, B and C
• Sensor class: includes methods to
communicate with sensor controllers 1, 2
and 3
Motor class methods: mutators
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•
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void forward(): motor rotates forward
void backward(): motor rotates backward
void stop(): stops with braking action
void flt(): motor floats to a stop
void reverseDirection(): changes from
forward to backward, or vice-versa
• void setPower(int power): sets motor
power; 7 is high, 0 low
Motor class methods: accessors
• int getPower(): returns current power setting
• char getID(): returns motor ID (A, B or C)
• All of the following methods return a boolean
value
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isBackward()
isFloating()
isForward()
isMoving()
isStopped()
Example
import josx.platform.rcx.*;
public class Patrol {
public static void main(String[] args) throws InterruptedException {
Motor.A.forward();
while (true) {
Motor.C.forward(); // go forward
Thread.sleep (5000);
Motor.C.reverse(); // turn around
Thread.sleep (1000);
}
}
Sensor class
• There are several types of sensors
available for the RCX, including:
– Touch
– Light
– Rotation
• Because each operates differently, there is
more complexity built into this class than in
most of the rest of the lejos API
Sensor Type and Mode
• A predefined set of constants is used to
describe:
– the kind of sensor attached to a particular
connector (type) and
– the kind of readings that are recorded by the
sensor (mode)
• These values as used as arguments to the
Sensor class’s setTypeAndMode method,
which is used to initially set up a sensor
Type and Mode examples
Sensor.S1.setTypeAndMode(1, 0x20);
// 1 represents touch sensor;
// 0x20 is boolean mode
Sensor.S1.setTypeAndMode(3, 0x80);
// 3 represents light sensor;
// 0x80 is percent mode
Example
import josx.platform.rcx.*;
public class GoForward implements SensorConstants {
public static void main(String[] args) {
Sensor.S2.setTypeAndMode(SENSOR_TYPE_TOUCH,
SENSOR_MODE_BOOL);
// sets up touch sensor using constants from SensorConstants interface
Motor.A.forward();
Motor.C.forward();
while( Sensor.S2.readValue() != 1 )
;
// loop ends (& robot stops) when bumper is touched
}
}
Methods of Sensor class
• public void activate ()
– activates sensor
– should be called after setTypeAndMode
• Methods that return Sensor readings:
– public final boolean readBooleanValue()
– public final int readValue()
– public final int readRawValue()
• Sensor readings can also be handled by a
SensorListener as described on the next slide
Sensor Listeners
• Sensor Listener interface specifies a single method:
public void stateChanged(Sensor s, int old, int new)
• s: event source
• old: previous value
• new: new value
• As with the GUI components we have looked at
before, the steps are
– define a class that implements the interface, and with the
code for the method
– add the listener to the appropriate Sensor
Serial class Methods
• The Serial class is used for RCX to IR and
RCX to RCX communication
• Methods work on the most basic level of
network communication, passing around
packets in the form of arrays of bytes
• A separate communications API provides
support for higher-level operations
One more example
import josx.platform.rcx.*;
public class ListenerExample implements SensorConstants, SensorListener {
public static void main(String[] args) {
ListenerExample exam = new ListenerExample();
Sensor.S1.setTypeAndMode(SENSOR_TYPE_TOUCH,
SENSOR_MODE_BOOL);
Sensor.S3.setTypeAndMode(SENSOR_TYPE_TOUCH,
SENSOR_MODE_BOOL);
Sensor.S1.addSensorListener(exam);
Sensor.S3.addSensorListener(exam);
exam.patrol();
}
Example continues
public void patrol () {
try {
Motor.A.forward();
while (true) {
Motor.C.forward();
Thread.sleep(3000);
Motor.C.backward();
Thread.sleep(1000);
}
} catch (Exception e) {
}
}
End of example
public void stateChanged(Sensor source, int oldValue, int newValue) {
if (newValue == 1)
if (source.getId() == 0)
Sound.playTone(220, 50);
else if (source.getId() == 2)
Sound.playTone(660, 50);
}
} // end class ListenerExample
// left bumper
// right bumper