Overview of ARM Jazelle Technology ARM offer a range of hardware architecture solutions to solve the performance requirements of managed execution environments such as Java and Microsoft Compact Framework. ARM Jazelle DBX (Direct Bytecode eXecution) technology for direct bytecode execution of JavaTM delivers an unparalleled combination of Java performance and the world's leading 32-bit embedded RISC architecture - giving platform developers the freedom to run Java applications alongside established OS, middleware and application code on a single processor. ARM Jazelle RCT (Runtime Compilation Target) technology supports efficient ahead-of-time (AOT) and just-in-time (JIT) compilation with Java and other execution environments. There are a number of ways for a virtual machine to execute bytecode: - Direct interpretation, where each bytecode is translated to machine code in software offers the most memory efficient solution. The vast majority of J2ME Java solutions in the market today use bytecode interpretation. Without hardware acceleration, direct interpretation may not have the performance required to run the more compelling applications.
- Just in Time (JIT) or Dynamic Adaptive Compilation (DAC) compilation, where code is first interpreted as above, and profiled to identify the most frequently executed code. These code segments are then compiled to native ARM code. The time taken to profile and compile code at run-time can result in excessive start-up times and jerkiness, resulting in a bad user experience. Code expansion or “bloat” is typically 4 to 8x the original bytecode, increasing memory and system cost and power consumption. Typical JIT and DAC compiler solutions are highly complex pieces of software and require significant effort to tune for the target platform, increasing cost of ownership.
- Ahead of Time (AOT) compilation, where the application is compiled either before download (at the server), compiled on installation (during device manufacture) or compiled while downloading the application for the first time. AOT compilation can deliver good performance, but can also be extremely costly in terms of memory code bloat, so selective AOT compilation is sometimes combined with JIT or interpreter techniques.
High Performance Jazelle DBX is widely used to deliver very high performance Java in mobile handsets and other consumer devices without impacting memory consumption, battery life or user experience. Jazelle RCT can be used to significantly reduce the code bloat associated with AOT and JIT compilation, making AOT technology viable on mass-market devices. It can also be used to support execution environments beyond Java, such as Microsoft .NET Compact Framework, Python and others. Excellent user experience The impact of application pauses during execution or slow start-times, due to the overhead of JIT compilation can be significant on a user - a 1 second pause in a game would render the device unusable. Jazelle DBX can be used to improve user experience and start time and reduce memory overheads when using a JIT, by reducing the amount of runtime compilation or replacing the JIT altogether. Jazelle RCT can be used to allow AOT compilation to be used more extensively and can also be combined with JIT technology on very high frequency platforms, where start-time and smoothness issues lessen. Low system cost Jazelle DBX and Jazelle RCT solutions are cache and memory efficient, maintaining low power while keeping system costs low through efficient memory and cache usage. Wide industry adoption and support Jazelle DBX is a robust and proven solution, integrated with Java platforms from leading third party software vendors and incorporated into solutions from most of the leading handset vendors worldwide as well as non-mobile consumer devices such as BluRay disc players. Jazelle DBX is simple to integrate, requires no time consuming compiler tuning for different platforms and applications and is supported by major Java platform vendors. Jazelle RCT provides an excellent target for any run-time compilation technology, including JIT and AOT for .NET MSIL, Python and Perl as well as Java. ARM is working with leading software providers to enable solutions ready for market with Jazelle RCT. Offering choice Through the development of extensions to the ARM architecture, our software products and industry partnerships, ARM enables our partners to deliver the very best solutions for execution environments. For example, for Java platforms, developers have the choice to: - Implement Jazelle DBX alone, for a resource constrained device where the available memory for a compiler or the JIT compile time overhead mean AOT or JIT are not suitable.
- On mid-range platforms that support Jazelle DBX and Jazelle RCT, utilize both, with Jazelle DBX for interpreted Java execution Jazelle RCT for selective AOT on a platform sensitive to user experience issues, such as start-time.
- Use Jazelle RCT for JIT and AOT, plus Jazelle DBX to improve start time and user experience issues with the JIT on a platform sensitive to user experience issues, such as start-time.
- On high-end platforms, use Jazelle RCT alone with JIT and AOT where, because the platform may be running at frequencies in the order of a GHz, issues such as start-time are lessened.
For more detailed information, please see the white papers and other Jazelle related web pages linked from here. Back to Top | 
