EEN-4 Embedded Systems Architecture. The ARM Instruction Set Architecture. Mark McDermott. With help from our good friends at ARM. ARM Instruction Set. This chapter describes the ARM instruction set. Instruction Set Summary. The Condition Field. Branch and Exchange. Jazelle DBX (Direct Bytecode eXecution) is an extension that allows some ARM processors to execute Java bytecode in hardware as a third execution state alongside the existing ARM and Thumb modes. Jazelle functionality was specified in the ARMv5TEJ architecture and the first The Jazelle instruction set is well documented as Java bytecode.
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The most prominent use of Jazelle DBX is by manufacturers of mobile phones to increase the execution speed of Java ME games and applications.
The published specifications are very incomplete, being only sufficient for writing operating system code that can support a JVM that uses Jazelle.
This tight binding facilitates that the hardware and JVM can evolve together without affecting other software. The Jazelle extension uses low-level binary translationimplemented as an extra stage between the fetch and decode stages in the processor instruction pipeline.
ARMv5 Architecture Reference Manual | ARMv5 Architecture Reference Manual – Arm Developer
Recognised bytecodes are converted into a string of one or more native ARM instructions. This is intended to significantly reduce the cost of interpretation. Among other things, this reduces the need for Just-in-time compilation and other JVM accelerating techniques.
Details are not arjv5tej, since all JVM innards are transparent except for performance if correctly interpreted. Jazelle mode is entered via the BXJ instructions. A hardware implementation of Jazelle will only cover a subset of Instructino bytecodes. For unhandled bytecodes—or if overridden by the operating system—the hardware will invoke the software JVM. The system is designed so that the software JVM does not need to know which bytecodes are implemented in hardware and a software fallback is provided by the software JVM for the full set of bytecodes.
The Jazelle instruction set is well documented as Java bytecode. However, ARM has not released details on the exact execution environment details; the documentation provided with Sun’s HotSpot Java Virtual Machine goes as far as to state: Employees of ARM have in the past published several white papers that do give some good pointers about the processor extension.
The Jazelle state relies on an agreed calling convention between the JVM and the Jazelle hardware state. The entire VM state is held within normal ARM registers, allowing compatibility with existing operating systems and interrupt handlers unmodified. Restarting a bytecode such as following a return from interrupt will re-execute the complete sequence of related ARM instructions.
c – List of Instruction Sets for Android – Stack Overflow
Specific registers are designated to hold the most important parts of the JVM state: Jazelle reuses the existing program counter PC or its instruxtion register R A pointer to the next bytecode goes in R14,  so the use of the PC is not generally user-visible except during debugging.
The “T”-bit must be cleared and the “J”-bit set. C0 C2 [bit 0] register must be set; clearing of the JE bit by a [privileged] operating system provides a high-level override to prevent application programs from using the hardware Jazelle acceleration.
The Java program counter PC pointing to the next instructions must be placed in the Link Register R14 before executing the BXJ branch request, as regardless insgruction hardware or software processing, the system must know where to begin decoding. Because the current state is held in the CPSR, the bytecode instruction set is automatically reselected after task-switching and processing of the current Java bytecode is restarted. Following an entry into the Jazelle state mode, aet can be processed in one of three ways: The third case will cause a branch to an ARM exception mode, as will a Java armg5tej of instructiob, which is used for setting JVM breakpoints.
Execution will continue in hardware until an unhandled bytecode is encountered, or an exception occurs. Between and bytecodes out of bytecodes specified in the JVM specification are translated and executed directly in the hardware. Low-level configuration registers, for the hardware virtual machine, are held in the ARM Co-processor “CP14 register c0”. The registers allow detecting, enabling or disabling the hardware accelerator if it is available.
In implementation terms, only trivial hardware support for Jazelle is now required: It was not at all specific to Java, and was fully documented; much broader adoption was anticipated than Jazelle was able to achieve. It integrated null pointer checking; defined some new fault mechanisms; and repurposed the bit LDM and STM opcode space to support a few instructions such as range checking, a new handler invocation scheme, and instrudtion. Accordingly, compilers that produced Thumb or Thumb2 code could be modified to work with ThumbEE-based runtime environments.
From Wikipedia, the free encyclopedia. Java programming language portal. Retrieved from ” https: ARM architecture Java virtual machine Interpreters computing.