picoJava

Abstract: Traditionally, the performance of a stack machine has been limited by the true data dependency. A performance enhancement mechanism, stack operations folding, was used in Sun Microelectronics' picoJava-I design, and it can fold up to 60% of all stack operations. The authors use the Java bytecode language as the target machine language, and study Java instruction folding on a proposed folding model, the POC model, which is used to illustrate the theoretical folding operations, Various practical folding strategies based on the POC model are introduced and evaluated. Statistical data show that the 4-foldable strategy eliminates 84% of all stack operations, and the 2-, 3-, and 4-foldable strategies result in overall program speedups of 1.22, 1.32 and 1.34, respectively, as compared to a stack machine without folding. Furthermore, the 4-foldable strategy is the most practical and cost effective of a Java stack machine design with a decoder width of 8 bytes. Circuit simulation results show that a 100 MHz 4-foldable folding mechanism can be realized with 0.6 /spl mu/m CMOS standard cells, or 240 MHz with 0.25 /spl mu/m CMOS technology.

Abstract: Traditionally, the performance of a stack machine was limited by the true data dependency. A performance enhancement mechanism-Stack Operations Folding-was used in Sun Microelectronics' picoJava design and it can reduce up to 60% of all stack operations. In this paper, we use the Java bytecode language as the target machine language, and study its instruction folding on a proposed machine model. Three folding strategies: 2-foldable, 3-foldable and 4-foldable, were simulated and evaluated. Statistical data show that our third folding strategy eliminates 73% of all stack operations, and each strategy has an overall program speedup of 1.19, 1.25 and 1.26, respectively, as compared to a traditional stack machine. Moreover, a Java machine model suitable for instruction folding, together with its pipeline stages, are presented. It seems to have the best cost/performance effectiveness of a Java stack machine if six bytes decoder width and the second folding strategy-the three-foldable strategy-are adopted.

Abstract: Through our experience in synthesis, validation, test, and integration of the picoJava processor core in a system-on-chip (SoC) design we point out the challenges faced and issues to address in efficient reuse of a soft core

Abstract: picoJava is a Java microprocessor developed by Sun to speedup execution of Java in embedded systems and an often-cited reference design for other Java processors. Information about implementations of picoJava is rare however. In contrast to a number of new Java processors which are targeted at FPGAs, picoJava was designed for ASICs, and no implementation in an FPGA is known up to date. In this paper we show the implementation and evaluation of Sun's picoJava-II microprocessor in an FPGA.