Memory access mechanism in embedded real-time Java processor

TL;DR: The memory access mechanism of JPOR-32 (32-bit Java Processor Optimized for RTSJ) is presented, which provides an efficient and convenient way to implement memory access, but also makes the contribution to the WCET predictability.

Abstract: Currently, Java has been gradually applied in such areas as robotics, industrial control, and other embedded real-time applications owning to its advantages like platform independence, robustness, security, etc. In order to improve the performance of Java's execution engine for embedded real-time applications, an embedded real-time Java processor JPOR-32 (32-bit Java Processor Optimized for RTSJ) is designed. In this paper, the memory access mechanism of JPOR-32 is presented. In JPOR-32, the optimized memory organization structure is designed to implement the runtime data areas of the Java virtual machine (JVM). Based on it, with the preprocessing operation, the memory access instructions optimization is implemented as well. The preprocessing operation enables the JVM's runtime operations involving dynamic loading, verification, preparation, resolution, etc. to be handled in advance. It not only provides an efficient and convenient way to implement memory access, but also makes the contribution to the WCET predictability. As to the memory management, in accordance with the Real-Time Specification for Java (RTSJ), garbage collection (GC) is not allowed in the immortal memory as well as the scoped memory, and in the heap, JPOR-32 adopts improved GC scheme suitable for embedded real-time Java environment. Besides, with the architectural support of the pipelined datapath, JPOR-32 provides effective supports for efficient and predictable memory access.