RoboCup Real-Time
Scheduling
Jonas Elmqvist (jonel@ida.liu.se)
Mikael Asplund (mikas@ida.liu.se)
Calin Curescu
Aleksandra Tesanovic
Mehdi Amarijoo
Real-Time Systems Laboratory
Department of Computer and Information Science
Linköping University
October 2007
Lesson Content
Goal of the lab
RoboCup physical and simulated scenario
Lab environment: platform and software
Lab assignments
Task scheduling
Road-map to successful labs
Requirements for passing
Resources
Practical issues
1
Goal of the Lab
to apply scheduling
theory to a pseudorealistic setting
to learn how to do
efficient resource
allocation in realtime systems
while having fun!
Real-time and embedded systems:
1. read sensor values
2. compute control values
3. output result of computation
image processing (1)
planner (2)
actuator (3)
What is RoboCup?
RoboCup: Robot world Cup
framework to foster intelligent robotics research
integrates wide range of technologies
a soccer game played by robots
RoboCup league consists of
our lab setup!
small-size soccer game
played by small robots on a small field ☺
big-size soccer game
played by big robots on a big field ☺
more info on RoboCup
http://www.robocup.org/
2
RoboCup Physical Scenario
RoboCup Physical Scenario
3
Simulated Scenario
Lab Assignments
Implement three schedulers
cyclic
earliest deadline first (EDF)
rate monotonic scheduler (RMS)
Implement one performance metric
deadline miss ratio
Develop and test schedulers using the
simulated environment
4
Lab Environment: Platform
Not many device drivers for real-time Linux
Windows and PC provide a nice interface to
camera and radio transmitters
Programming language Java
constraints
avoid low-level programming
minimize effort to learn a new language
ADA has lost popularity in the industry
C is too low-level
Lab Environment: Software
Image Processing
Low-Level Controller
High-Level Controller
Planner
Reactor
Actuator
5
High-Level Control
Planner
produces abstract actions based on the image
processing information
any-time planner
executes the plan in six plan steps
should restart periodically to make a new plan
typically every 1 second
High-Level Control
Reactor
produces low-level actions based on the
abstract actions of the planner
reevaluates actions in every cycle
fairly independent of the planner
sends commands to the actuator
runs
after image processing
before actuator
6
Task Scheduling
Tasks in the system...
...are
image processing (1x)
planner (3x)
reactor (3x)
actuator (1x)
...have precedence constraints (not independent!)
...have temporal attributes
(estimated) worst-case execution time
period
relative deadline
Task Temporal Attributes
Task name
Estimated WCET (µs)
Period (µs)
Relative
deadline (µs)
(computation time)
Image
processing
100000
50000
50000
Planner
(all 6 steps)
12000
(2000 per step)
1000000
1000000
Reactor
1000
50000
50000
Actuator
3500
50000
50000
7
Cyclic Scheduling
Schedule is a predefined sequence of calls to
tasks
Consists of
major cycle
minor cycle
Major cycle
a whole non-repetitive sequence
consists of a number of minor cycles
Minor cycle
dictated by the clock interrupts
major cycle
minor cycle
interrupts
Cyclic Scheduling: your task
Make cyclic scheduling for the RoboCup task set
Determine the length of the major and minor
cycles
Determine the number of minor cycles
In the minor cycle
image processing, reactor, and actuator run to
completion
planner executes one or more plan steps
Restart the planner in an appropriate place in
the schedule
remember: planner should be restarted every second!
keep this in mind when determining the length of the
major cycle!
8
Priority Driven Scheduling
Scheduler
dispatch
Tasks in three states
ready
running
suspended
Ready
Running
preempted
released
Suspended
Two type of priority lists maintained by scheduler
ready lists
sorted according to scheduling policy, e.g., EDF and RMS.
suspended lists
sorted according to their release times
initially all tasks are in the suspended list
Priority Driven Scheduling: Your task
Write the part of the scheduler code that maintains the
priority lists as follows
Task is ready to be released
should be moved to ready list
Tasks in the ready state
the task with the highest priority should be executed (by
“firing” it)
Make sure that the planner is appropriately restarted
9
Priority Driven Scheduling: Your task
Running task(s)
return on specific yield points
can be preempted
can miss the deadline
scheduler should detect missed deadlines and invoke deadline miss
handler
getDeadlineMissHandler().handleAsynchEvent()
once finished (isfinished=true) task should be suspended
new release time and deadline should be set
NOTE: you should not have busy loops in the scheduler
if there are no task ready to run then scheduler should wait until
there are tasks
use the sleep() function of the Scheduler
Road-map to Success
Understand the RoboCup scheduling problem by reading the
compendium before the first lab occasion
you need this to be able to set-up and run your lab
Download studentFiles.exe file
download procedure and location of the files is in the compendium
extract exe file to your home directory
you get code skeletons for two first schedulers (cyclic and EDF)
RMS you should implement from scratch
Configure the test environment for running the schedulers
instructions in the compendium
Implement and test you algorithms
against another student team
against the reference schedulers
Join a final demo of some actions taking place in the physical
environment (date to be announced) and have some fun!
10
Requirements for Passing
Examination consists of two parts
practical part
theoretical part
Practical part
demonstration of working solutions of
schedulers to the lab assistant
Theoretical part
extensive discussion with the assistant on the
questions from the compendium
Words of Wisdom
Be prepared to elaborate on all questions from the
compendium during the theoretical part of the examination!
Answers to preparatory questions should be prepared
before the lab!
All members of the lab group should be present and
actively involved in every segment of the examination!
Passiveness in examination could result in extra assignments for
passing
Do the lab assignments before the deadline: December 6th!
11
Resources
TDDB47 web pages
address: http://www.ida.liu.se/~TDDB47
all important information and news will be posted there
check web regularly for news and important info
pay special attention to the first page and the ”Labs” page
Compendium
contains all the details on the lab exercises
contains instructions for setting up and running the lab
contains most relevant RoboCup APIs
Complete APIs for the RoboCup
http://www.ida.liu.se/~m_reap/RoboCup/API
or the TDDB47 web pages
Practical Isssues
Labs are done in PC rooms at IDA
Java version used in RoboCup is 1.4.2_05
Available tools for programming
Emacs
Eclipse
Netbeans
Working with Emacs (recommended)
Start->Programs->GNU Emacs->Emacs
Compile in the command prompt with ”javac”
See handouts of lesson 2 for more details
Eclipse/Netbeans
Configuration required
12
Java Basics
- for RoboCup Lab Jonas Elmqvist (jonel@ida.liu.se)
Mikael Asplund (mikas@ida.liu.se)
Calin Curescu
Aleksandra Tesanovic
Mehdi Amarijoo
Real-Time Systems Laboratory
Department of Computer and Information Science
Linköping University
October 2007
This Lesson
„
Gives an introduction to Java language
„
Provides an overview over basic knowledge
required by unskilled Java programmers to
program the RoboCup lab assignments with
success
„
Focuses on specific issues required for
programming the RoboCup lab assignments
„
Tailored for students that have some experience
with object-oriented programming (e.g., C++)
1
Motivation: RoboCup Lab
Lesson Content
Java overview and features
„ Control Statements
„ Variables
„ Classes and inheritance
„ Type conversion
„ Operator summary
„ Compiling and running programs
„ Resources
„
2
Java Programming: an Overview
Java Programming
Java Platform
myScheduler.java
myScheduler.class
compiler
program
bytecode
Java Virtual
Machines
interpreter
(JVM)
interpreter
myScheduler.java
Java API
(+RoboCup API)
_______________
JVM
Hardware Platform
my
scheduler
Windows
my
scheduler
Java (+RoboCup)
Platform
Solaris
Java Features
Object oriented language
„ Interpreted at runtime
„ Garbage collection
„
Java
runtime environment deletes objects that
are no longer being used
different than in C++!
automatic deletion of objects=>
no deconstructors
Strong type checking
„ Exception handling
„
3
Control Flow statements
similar to C and C++!
„
Loops
„
Branching
„
while, do…while , for
if…else, switch…case
Exceptions
try…catch…finally,
„
throw, throws
Aborts
break,
continue, label:, return
Scope of these is block dependent
Classes
public class Scheduler{
public string PolicyName;
public Scheduler() {…}
public void fireThread(RealtimeThread s){
s.run();
}
Variable
Constructor
CLASS
Method
}
„
constructor does not have to be specified
„
system uses default constructor
default constructor does nothing
classes have modifiers
public, protected, private
„
a class is an implementation of an interface
„
public static void main(String[] args)
interface is Java’s response to multiple inheritance
method used for executing a program
similar to C++!
4
Variables in Java
„
declaration:
type name
RLThread newThread
„
can be declared as static
„
class-wide, same value for all
instance of the class
have modifiers
access modifiers: public,
protected, private
static, final, volatile
„
Class member
variable scope
class Scheduler{
public string PolicyName;
Method Parameter
Scope
public void fireThread
(RealtimeThread s)
{
...
Local block
variable
if (..)
scope
{
int i=7;
}
System.out.println("The value of i = "+i);
}
are valid within a scope
similar to C++!
}
Error
(”i” does not exist out of scope)
Variable Types
„
Primitive type
byte,
short, int, long
float, double
char, boolean
„
Reference type
double missedDeadlines= 0.0;
manipulation of the value!
similar to C++!
RTLThread newThread;
reference
is a memory
manipulation of the address!
address (pointer in C++)
arrays are objects and are of reference type
all objects are manipulated by Java using
their references!
5
Object Creation
are created from a class (as you know)
„
AbsoluteTime abs= new AbsoluteTime();
class
object name
allocates space
for an object
objectReference.variableName
used as in C++
„
constructor
manipulate
or inspect its variables
call its methods
remember that objects are of reference
type
„
Methods
„
represent the
behavior of a class
„
several
input
one output (return)
class Scheduler{
public string PolicyName;
public void fireThread(RealtimeThread s){
s.run();
}
}
modifier
output
input
have parameters
„
and modifiers
public,
protected,
private
static, final,
synchronized, native
OBS! Value of the address is passed if an input parameter is an object !
6
Example
public void tricky(Point arg1, Point arg2) {
Point temp = arg1;
arg1 = arg2;
arg2 = temp;
arg2.x = 200;
}
What is the value of p1.x, p2.x after the following
sequence of statements?
p1.x = 50;
p2.x = 100;
tricky(p1,p2);
Inheritance
public class EarliestDeadlineFirstScheduler extends Scheduler{…}
Subclass (EarliestDeadlineFirstScheduler) inherits all
members of superclass (Scheduler)
„ Exceptions to inheritance are when
„
members
are not accessible (i.e., private)
members are explicitly overridden (i.e.,
redefined) in subclass
„
Constructors are not inherited
7
Type Conversions (Casting)
Object casting!
„
Upcast (widening conversion)
from
subclass to ancestor
usually automatic; always safe
„
Downcast (narrowing conversion)
from
ancestor to subclass
checked at runtime for validity
if not an instance – an Exception is thrown
„
”instanceof” operator can be used to
check if an object belongs to a class
Operators
Priority Operators
[ ]
1
2
3
()
method call
.
member access
++
pre- or postfix increment
--
pre- or postfix decrement
+ -
unary plus, minus
~
bitwise NOT
!
boolean (logical) NOT
(type)
type cast
New
object creation
* / %
multiplication, division, remainder
+ -
4
+
5
6
Operation
Associativity
Priority
array index
addition, substraction
left
signed bit shift left
>>
signed bit shift right
>>>
unsigned bit shift right
< <=
less than, less than or equal to
> >=
greater than, greater than or equal to
Instanceof
reference test
Operation
==
equal to
!=
not equal to
7
&
bitwise AND
&
boolean (logical) AND
8
^
bitwise XOR
^
boolean (logical) XOR
9
right
Associativity
left
left
left
|
bitwise OR
|
boolean (logical) OR
11
&&
boolean (logical) AND
12
||
boolean (logical) OR
left
left
13
? :
conditional
right
=
assignment
left
14
*= /= += -= %= <<=
combinated assignment
10
left
left
left
string concatenation
<<
Operators
right
>>= >>>= &= ^= |= (operation and assignment)
left
8
Code Organization
Each class is in its own .java file
„
ClassName has to be the same as FileName
in CyclicScheduler.java:
public class CyclicScheduler extends BasicScheduler
exception is that inner classes contained wihin the class do
not have its own .java file
Related classes are grouped
in packages”
„
in CyclicScheduler.java:
similar to namespaces in C++
packages are structured hierarchically
each .java file should start with
the declaration of the package
package rt;
import soccorob.rt.*;
import soccorob.ai.agent.*;
public class CyclicScheduler
extends BaseCyclicScheduler {
Import allows you to use
short names for classes
„
Compiling (*.java Æ *.class)
„
correct compiling depends on setting the CLASSPATH
environment variable
points to the directories under which the compiler can find
classes on which new compiled class depends
In Windows:
set CLASSPATH=%CLASSPATH%;c:\ programs\Robolab;z:\robolab
„
Class files must respect the package hierarchy
„
„
class rt.CyclicScheduler should be in CLASSDIR\rt\, where
CLASSDIR is contained in CLASSPATH
Compiling command example
javac [–classpath C:\programs\Robolab] CyclicScheduler.java
”-classpath ...” option can be used instead of the CLASSPATH
variable
9
Running the program
„
Result of the compilation is a .class file
sorted
„
„
in the same directory as the source file
Can be changed with ”–d DestinationDirectory”
command for running the program
java
myPackage.ClassName
Example with this and super
this
Can
be used to access
methods or fields
Reference to “this ” object
can be in a return
statement
super
Only
for accessing the
parent’s methods or fields
public class HelloWorld extends Hello {
String msg;
public HelloWorld(String message) {
super(message);
msg = message;
}
public HelloWorld() {
this("hello world");
}
public void changeMsg(msg) {
this.msg = msg;
}
public HelloWorld returnMe() {
return this;
}
}
10
Printing
„
Standard I/O: stdin, stdout, stderr
defined in java.lang.System object as
public static final InputStream in;
public static final PrintStream out;
„
Escape codes for
unprintable characters:
\b - Backspace
\t - Tab
\n - Newline
\f - Form feed
Example
String mes1 = ”Hello World\nSecond line:”;
String mes2 = ”\tValue of ion =”
String mes3 = mes1 + mes2;
int ion = 3;
System.out.println(mes3);
System.out.println(mes2 + ion);
\r - Carriage return
\‘ - Single quote
\” - Double quote
\\ - A backslash
\nnn - The character with
octal value nnn
('\012' == '\n')
Resources
„
On-line tutorials
Help
you to learning the Java language
Provide
explantions for essential Java classes
Available
at
http://java.sun.com/docs/books/tutorial/
11
THE END
RoboCup Example 1
Class
Relevant Members
HighResolution
Time
setTime(HighResolutionTi
AbsoluteTime
me new)
ReleaseParamet
.....
ers
Subclass
Relevant members
....
PeriodicParameters
...
...
AbsoluteTime getStart()
RealtimeThread
ReleaseParameters
getReleaseParameters()
....
RLThread
....
ThreadNode
....
RMThreadNode
AbsoluteTime deadline
AbsoluteTime nextRelease
Assume:
RLThread[] threadList=(RLThread[]) getThreads();
threadNode= new RMThreadNode(threadList[i]) ;
How can we set the next release time of the threadNode (using setTime). The
value of the (old) release time of the thread can be obtained using
getRealeseParameters.
What should follow?
12
RoboCup Example 1
This statement:
threadNode.nextRelease.setTime(((PeriodicParameters)thr
eadList[i].getReleaseParameters()).getStart());
...is equivalent with:
AbsoluteTime nextRel = threadNode.nextRelease; RLThread
thr = threadList[i];
ReleaseParameters ppo = thr.getReleaseParameters();
PeriodicParameters pp = (PeriodicParameters)ppo;
AbsoluteTime sTime = pp.getStart();
nextRel.setTime(sTime);
When not sure use ”()” to enforce presedence.
Expression between ”()” is always evaluated first!
RoboCup Example 2
Class
Relevant Members
RLThread
ThreadNode
ThreadNode next
ThreadNode previous
RLThread
thread
Subclass
Additional members
PlannerControl
restart()
RMThreadNode
AbsoluteTime deadline
AbsoluteTime nextRelease
Assume:
RLThread[] threadList=(RLThread[]) getThreads();
threadNode= new RMThreadNode(threadList[i]) ;
How can we restart the planner of the threadNode in the list?
What should follow?
13
Other examples
What is the result of the following
statements?
„ System.out.println(”temperature is ”+3+2);
„ System.out.println(”temperature is
”+(3+2));
„ (PlannerControl)threadList[1].restart();
„ ((PlannerControl)threadList[1]).restart();
14