Java and Embedded Linux Systems

Java in Embedded Linux Systems

Java in Embedded Linux Systems Michael Opdenacker Free Electrons http://freeelectrons.com/

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Java history Java implementations Key concepts and features JVM implementations Issues with Java Java hardware Java's strengths for acceleration and Linux embedded systems Conclusion Glossary Useful reading

1991: Sun started working on a project to anticipate the next wave of computing: the convergence of digitally controlled consumer devices and computers. 1992: Implemented home entertainment control demos with a processor independent language: Oak. 19921994: focus moving from digital cable television network to the Internet as a way to publish and share content. 1994: Oak renamed as Java 1994: HotJava web browser with dynamic, executable content. 1995: First public release of Java. Great success

1995: Netscape announced support for Java 1996: Java 1.0 release 1996: Microsoft takes a Java license 19972001: Sun sues Microsoft for trying violating its license and trying to enforce its own Java standard. 2001: Microsoft loses the right to advertise its products as “Java Compatible”. Microsoft's licensed terminated but can continue to use its own implementations. 1998: Java 1.2. Renamed as “Java 2” 2002: Java 1.4

WORE Write Once, Run Everywhere Java applications are compiled in Java Virtual Machine (JVM) bytecode. Can be run on any platform with a JVM implementation.

Java Java JVM Developer source code Compiler binary environment

JVM JVM User binary Interpreter environment

See http://java.sun.com/docs/overviews/java/javaoverview1.html for details Simple Portable Automatic garbage collection, small footprint No architecture dependent data sizes (int: 32 bit, float: 32 bit). Portable VM source C code. Object oriented For well defined, reusable sw components Interpreted On the fly conversion to native machine code NetworkSavvy Support for network protocols (http, ftp...) High performance VM code designed for simple machine code Robust generation. Optimized bytecode generated by the No pointers, no memory corruption, true compiler. VM interpreter optimizations. arrays. Strict compile and run time checking. Multithreaded Secure Multithread support in the language itself. But Built for security in networking environments. Realtime performance limited by OS RT perf. Data protection (no pointers). Dynamic Architecture neutral Upgrading a class doesn't force to recompile the Code runs anywhere a VM is available applications using it.

Helps to understand how you can access the hardware with the JVM! The JNI lets code running on the JVM operate with applications and libraries written in other languages such as C, C++ or assembly. Needed to use system dependent routines handling hardware access.

Though sources are available, Java is not Open Source Must purchase support from Sun to access the Java Compatibility Kit, mandatory if you release a product with changes to the Java sources. Commercial applications must purchase a license for the Java Compatible logo. Limitations of the Write Once Run Everywhere paradigm: the availability of a JVM is not enough Also need the full set of JDK libraries Can't run Sun's JDK classes on any JVM: they assume that a bunch of native methods are implemented. These methods are undocumented!

Hides the specificities of the device and the embedded OS Provides a number of features beyond those offered by the OS Allows to build network interoperable embedded systems, whatever their hardware architecture. Simplifies product development. The software can easily be developed on workstations in parallel with the hardware. Makes it possible to reuse code Easy integration of Java Code and native code Smaller applications footprint: more compact bytecode and higher level class availability.

See http://java.sun.com/products/ JDK: Java Development Kit JVM: Java Virtual Machine J2RE: Java2 Release Environment Everything needed to run Java applets and applications: JVM, classes... J2SE: Java 2 Standard Edition J2RE + development tools (JDK) J2EE: Java 2 Enterprise Edition Java tools for building enterpriseclass serverside applications J2ME: Java 2 Micro Environment Highly optimized Java runtime environment and APIs for a wide range of consumer electronics products.

Java implementations for Linux

Java in Embedded Linux Systems © Copyright 20062004, Michael Opdenacker, Creative Commons AttributionShareAlike 2.0 license http://freeelectrons.com Aug 9, 2006 13 Blackdown project http://www.blackdown.org/ Complete JDE and JRE releases for Linux Just ports Sun's Java tools to Linux, entirely based on Sun sources (because of the license) Just distributes binaries, no source code. Did its own for several years, until Sun started supporting Linux and used their work Now works together with Sun (who granted a special noncommercial license)

Reasons for choosing Sun Java for Linux Sun Java on Linux is mostly based on Blackdown's work Commercial support Supports only 32bit x86 and Sparc Linux Reasons for choosing Blackdown Java for Linux Vendor independent, non commercial, focusing only on technical issues No commercial support Available on other architectures (ARM, PowerPC, MIPS...) Provide additional packages for Java2: Java3D, Java Advanced Imaging, Java Media Framework (audio, video)

Java in Embedded Linux Systems © Copyright 20062004, Michael Opdenacker, Creative Commons AttributionShareAlike 2.0 license http://freeelectrons.com Aug 9, 2006 15 GNU and Java http://www.gnu.org/software/java/ 2 components: Java Compiler: gcj and libgcj GNU Classpath

Java in Embedded Linux Systems © Copyright 20062004, Michael Opdenacker, Creative Commons AttributionShareAlike 2.0 license http://freeelectrons.com Aug 9, 2006 16 GNU compiler for Java http://gcc.gnu.org/java/ libgcj: runtime for gcj compiled gcj can compile: applications Java source code directly to native core class libraries machine code garbage collector Java source code to Java bytecode bytecode interpreter (class files) Java bytecode to native machine Most Java API classes supported code. (AWT not yet). Merge in progress with Classpath. gcj can also be configured as a crosscompiler! gdb is supported

Java in Embedded Linux Systems © Copyright 20062004, Michael Opdenacker, Creative Commons AttributionShareAlike 2.0 license http://freeelectrons.com Aug 9, 2006 17 GNU Classpath http://www.gnu.org/software/classpath/ Java classes implementation from the GNU project License: GNU GPL, which an exception for linking with this library. So, no license issue with proprietary Java programs. Exhaustive Java API implementation. Even AWT and a preliminary Swing implementation are available in the snapshot releases.

Java in Embedded Linux Systems © Copyright 20062004, Michael Opdenacker, Creative Commons AttributionShareAlike 2.0 license http://freeelectrons.com Aug 9, 2006 18 IBM's Java on Linux http://www106.ibm.com/developerworks/java/jdk/linux140/ Complete implementation from IBM: J2SE, J2EE, J2ME, including IBM's VM. Supported Linux platforms (only in 32 bit mode) IA32, AMD64, Itanium, PowerPC 64 bit, zSeries IBM's implementations Reengineered Java Machine, IBM's Just In Time compiler... Java is at the core of IBM's strategy (WebSphere in particular)

Free Software JVMs

Java in Embedded Linux Systems © Copyright 20062004, Michael Opdenacker, Creative Commons AttributionShareAlike 2.0 license http://freeelectrons.com Aug 9, 2006 20 Kaffe http://www.kaffe.org/ Cleanroom JVM implementation plus associated class libraries needed by a Java runtime environment (didn't use Sun sources) Not an officially licensed JVM implementation. Not fully compatible with Java specs and lacks some key features (security, etc.) Supported in several platforms: x86, arm, mips, m68k, ppc... Great for VM education or research, or in a Free Software Java distribution. License: GNU General Public License

Java in Embedded Linux Systems © Copyright 20062004, Michael Opdenacker, Creative Commons AttributionShareAlike 2.0 license http://freeelectrons.com Aug 9, 2006 21 SableVM http://sablevm.org/ “A robust, clean, easy to maintain and extend, extremely portable, efficient, and specificationcompliant Java virtual machine” Clean room JVM implementation Roughly supported on most architectures supported by Linux (ARM in particular) Compatible with JVM and Java Language specifications License: GNU Lesser General Public License Uses GNU Classpath (GPL with an exception for linking)

Java in Embedded Linux Systems © Copyright 20062004, Michael Opdenacker, Creative Commons AttributionShareAlike 2.0 license http://freeelectrons.com Aug 9, 2006 22 Jikes RVM http://oss.software.ibm.com/developerworks/opensource/jikesrvm/ RVM: Research Virtual Machine Open Source (Common Public License) implementation from IBM Implemented on Java, running on itself without requiring a second virtual machine Supported Linux Platforms: x86 and PowerPC Relies on GNU Classpath.

Some ARM cores directly support Java bytecode execution (Jazelle technology): http://www.arm.com/products/solutions/Jazelle.html Those cores are supported by Linux However, Linux currently doesn't support their Java capabilities Actually, several specific JVMs are said to take care this by themselves, without involving the OS. Not enough details available!

Java has great competitive advantages for developing applications for operating systems Sun's Java is not Free Software However, Free Software implementations for GNU / Linux are available now and satisfy most needs Unfortunately, Java hardware acceleration is not supported yet by Linux.

Embedded Java+Linux reference: http://www.linuxdevices.com/articles/AT8918758707.html Java overview and history: http://en.wikipedia.org/wiki/Java_programming_language

This document belongs to the more than 1000 page materials of an embedded GNU / Linux training from Free Electrons, available under a free documentation license. http://freeelectrons.com/training Linux on TI OMAP processors Introduction to Unix and GNU/Linux Free Software development tools Embedded Linux kernel and driver development Introduction to uClinux Free Software tools for embedded Linux systems Realtime in embedded Linux systems Audio in embedded Linux systems What's new in Linux 2.6? Multimedia in embedded Linux systems Java in embedded Linux systems How to port Linux on a new PDA http://freeelectrons.com/articles

Embedded Linux optimizations Embedded Linux from Scratch... in 40 min!

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Java in Embedded Linux Systems © Copyright 20062004, Michael Opdenacker, Creative Commons AttributionShareAlike 2.0 license http://freeelectrons.com Aug 9, 2006 29 Embedded Linux Training Free Electrons services Unix and GNU/Linux basics Linux kernel and drivers development Realtime Linux uClinux Custom Development Development and profiling tools System integration Lightweight tools for embedded systems Embedded Linux demos and prototypes Root filesystem creation System optimization Audio and multimedia Linux kernel drivers System optimization Application and interface development

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