Embedded Java ResearchEmbedded Java Research

Geoffrey BeersGeoffrey Beers

Peter JantzPeter Jantz

December 18, 2001December 18, 2001

Advantages of the Java Advantages of the Java Technology ModelTechnology Model

SimplicitySimplicity– Easier language to learn than traditional C/C++ and still has Easier language to learn than traditional C/C++ and still has

object-oriented methodology.object-oriented methodology. Security and SafetySecurity and Safety

– Java programs have more robust security checking, with the Java programs have more robust security checking, with the RTE creating a “sandbox” where applications can run RTE creating a “sandbox” where applications can run safely.safely.

– Lack of pointers eliminates direct memory accessLack of pointers eliminates direct memory access Portability and Robust DistributionPortability and Robust Distribution

– Applications can be easily developed on desktop systems Applications can be easily developed on desktop systems and ported, with minimal effort, to target device.and ported, with minimal effort, to target device.

– ““Write-once, run anywhere” mentality.Write-once, run anywhere” mentality.

Disadvantages of Embedded JavaDisadvantages of Embedded Java

Huge speed disadvantage. Interpreted Java code is Huge speed disadvantage. Interpreted Java code is still 5-10 times slower than a similar C still 5-10 times slower than a similar C application.application.– Improvements made to JVM technology have enhanced Improvements made to JVM technology have enhanced

this over the years.this over the years.

– Often based on how the application is writtenOften based on how the application is written» A well-written Java program can out-perform a poorly written A well-written Java program can out-perform a poorly written

C programC program

– For embedded applications do we really need to For embedded applications do we really need to interpret code, or can we use interpret code, or can we use native-compiled codenative-compiled code??

Disadvantages of Embedded JavaDisadvantages of Embedded Java

Embedded Java technology still relatively new and Embedded Java technology still relatively new and industry support has been slow to catch-on.industry support has been slow to catch-on.

Biggest disadvantage: Lack of RTOS support or Biggest disadvantage: Lack of RTOS support or standardstandard– Early embedded Java applications were very similar to Early embedded Java applications were very similar to

conventional desktop programs. Fine for some apps, conventional desktop programs. Fine for some apps, but deadline control and interrupt handling are but deadline control and interrupt handling are necessary.necessary.

– Great improvement in this genre since 1998.Great improvement in this genre since 1998.

Real-Time Specification for Java Real-Time Specification for Java Guiding PrinciplesGuiding Principles

Applicability to particular Java environments.Applicability to particular Java environments.– Do not include specs that restrict use to a particular Do not include specs that restrict use to a particular

Java environment.Java environment.

Backward compatibilityBackward compatibility– RTSJ shall not prevent existing, non real-time Java RTSJ shall not prevent existing, non real-time Java

programs, from executing on implementations of the programs, from executing on implementations of the RTSJ.RTSJ.

““Write once, run anywhere” mentality should be Write once, run anywhere” mentality should be followed as much as possible.followed as much as possible.

RTSJ Guiding Principles (cont.)RTSJ Guiding Principles (cont.)

RTSJ should address real-time system practice and RTSJ should address real-time system practice and allow for the incorporation of advanced features in allow for the incorporation of advanced features in the future.the future.

Predictable execution as first priority in all Predictable execution as first priority in all tradeoffs.tradeoffs.– May come at expense of general-computing May come at expense of general-computing

performance, but will allow for greater real-time performance, but will allow for greater real-time integration.integration.

No syntactic extensionNo syntactic extension– RTSJ will not introduce new keywords or other RTSJ will not introduce new keywords or other

syntactic extension to the Java language.syntactic extension to the Java language.

Real-Time Specification for JavaReal-Time Specification for Java

Finalized in November 2001.Finalized in November 2001. Standard specification for garbage Standard specification for garbage

collection, memory management, and collection, memory management, and task/thread control.task/thread control.

Additional classes and extensions to Additional classes and extensions to standard Java JDK.standard Java JDK.– However, no new syntax was necessary.However, no new syntax was necessary.

javax.realtimejavax.realtime Package Package

Real-time specification provides Real-time specification provides modifications to the Java Language Spec. modifications to the Java Language Spec. and JVM Spec.and JVM Spec.

New APIs to enable the creation, New APIs to enable the creation, verification, analysis, execution, and verification, analysis, execution, and management of real-time Java threads.management of real-time Java threads.

New APIs in a standard extension package, New APIs in a standard extension package, javax.realtimejavax.realtime..

Seven Areas of EnhancementSeven Areas of Enhancement

Thread scheduling and dispatchingThread scheduling and dispatching Memory managementMemory management Synchronization and resource sharingSynchronization and resource sharing Asynchronous event handlingAsynchronous event handling Asynchronous transfer of controlAsynchronous transfer of control Thread terminationThread termination Physical memory accessPhysical memory access

Four Memory AreasFour Memory Areas

Scoped MemoryScoped Memory– Objects have lifetime defined by syntactic scope.Objects have lifetime defined by syntactic scope.

Physical MemoryPhysical Memory– Objects created within specific physical memory Objects created within specific physical memory

regions having certain characteristics.regions having certain characteristics. Immortal MemoryImmortal Memory

– Objects cannot be destroyed; once allocated they stay Objects cannot be destroyed; once allocated they stay until the end of the application.until the end of the application.

Heap MemoryHeap Memory– Objects represent an area of memory on the heap.Objects represent an area of memory on the heap.

Asynchronous EventsAsynchronous Events

Some internal or external event that Some internal or external event that happens.happens.– Not all real-life events are predictable in time Not all real-life events are predictable in time

and frequency.and frequency. System needs to respond to the changing System needs to respond to the changing

environment.environment.– Ability of real-time systems to react to the Ability of real-time systems to react to the

events requires reliable asynchrony techniques.events requires reliable asynchrony techniques.

Major Platforms SupportedMajor Platforms Supported

Operating SystemsOperating Systems– Windows CEWindows CE– LinuxLinux

ProcessorsProcessors– PicoJava – Sun’s Java ProcessorPicoJava – Sun’s Java Processor– StrongArmStrongArm– MIPsMIPs– IntelIntel

Java and Embedded LinuxJava and Embedded Linux

Java does I/O by opening files which are the Java does I/O by opening files which are the Linux device drivers (ex: /dev/mem). Java Linux device drivers (ex: /dev/mem). Java can seek in addition to read, write and open.can seek in addition to read, write and open.

Bootstrapping allows Linux to load necessary Bootstrapping allows Linux to load necessary drivers and networking files and start running drivers and networking files and start running the JVM.the JVM.

Standard Linux distributions with networking Standard Linux distributions with networking support require lots of memory. support require lots of memory.

Improving PerformanceImproving Performance

Java bytecode programs are typically 10 Java bytecode programs are typically 10 times slower than programs written in C or times slower than programs written in C or C++.C++.

How well the program is written is more How well the program is written is more important. A well-written Java program can important. A well-written Java program can equal the efficiency of an average-written equal the efficiency of an average-written C/C++ program.C/C++ program.

Interpreting code uses less ROM.Interpreting code uses less ROM.

Compilation into Native CodeCompilation into Native Code

AOT (Ahead of time) AOT (Ahead of time) JIT (Just in time)JIT (Just in time) Dynamic CompilationDynamic Compilation

AOT CompilationAOT Compilation

Similar to C compilersSimilar to C compilers Tends to create large executablesTends to create large executables Need to re-compile for different platforms Need to re-compile for different platforms

or when loading a different classor when loading a different class Can compile everything including class Can compile everything including class

librarieslibraries

JIT CompilationJIT Compilation

Machine independentMachine independent Higher startup costHigher startup cost Not ideal for embedded systemsNot ideal for embedded systems

– Requires fast CPU, lots of virtual memory and Requires fast CPU, lots of virtual memory and a fast disk drive for paginga fast disk drive for paging

Dynamic CompilationDynamic Compilation

Dynamically compiles code that is being Dynamically compiles code that is being used more frequentlyused more frequently

Typically uses JIT compilersTypically uses JIT compilers Doesn’t require virtual memory, adaptable Doesn’t require virtual memory, adaptable

to available system memoryto available system memory Isn’t guaranteed to meet timing constraintsIsn’t guaranteed to meet timing constraints

– Applications can change the compiler’s thread Applications can change the compiler’s thread priority for greater predictabilitypriority for greater predictability

Other Methods to improve Other Methods to improve PerformancePerformance

Static Linking - place bytecode into ROMStatic Linking - place bytecode into ROM Re-write bytecode interpreter in assembly Re-write bytecode interpreter in assembly

languagelanguage Use a Java ChipUse a Java Chip

Conclusions and SummariesConclusions and Summaries

Recent advances in embedded Java technology Recent advances in embedded Java technology and advent of RTSJ are allowing real-time and advent of RTSJ are allowing real-time capabilities and possibilities in the Java world.capabilities and possibilities in the Java world.

Many current embedded Java systems are non Many current embedded Java systems are non real-time or a limited subset of RTSJ principles.real-time or a limited subset of RTSJ principles.

Sun’s advancements and broad range of Sun’s advancements and broad range of distribution environments make embedded Java distribution environments make embedded Java programming much simpler and more robust.programming much simpler and more robust.