在嵌入式爪哇虛擬機器中設計並實做動態電壓頻率調整技術

Abstract

在執行程式過程中動態改變處理器的電壓以及執行頻率（Dynamic Voltage and Frequency Scaling, DVFS）可顯著的降低電耗。因為JAVA在嵌入式系統上受到重視，所以本論文在嵌入式JAVA虛擬機器上發展了一套完整的DVFS實作。我們修改現有的DVFS策略，其主要參考目前工作的程式中記憶體存取時間以及處理器計算時間的比例，計算適合的電壓，節省電耗。修改並發展出一套完整的方法論，在不同的平台下都可以用類似的方式來估算記憶體存取時間以及處理器計算時間的比例，其誤差在本論文的實驗環境下小於8%。實做之DVFS系統包含兩種運作方式，其中以時間間隔為基礎的方式可以在效能損失15.89%~ 41.16%的情況下，達到12.04%~28.68% 的電耗節省。 我們同時驗證，以函式方法為基礎的系統並不適合使用於嵌入式爪哇虛擬機器中。

Dynamic voltage and frequency Scaling (DVFS) is recognized as one of the most effective power reduction techniques. JAVA is getting popular in mobile embedded systems in recent year. Thus we propose a low-power research platform on an embedded JVM and implement DVFS on it. We refer to an accurate DVFS algorithm which calculates proper frequency of a program according to the ratio of on-chip computation time to off-chip access time. Proposed methodology for estimating the ratio of on-chip computation time to off-chip access time can be applied on defacement platforms. On our experiment platform, average error of estimations is less than 8%. Implemented design contains two schemes. Proposed interval-based design reduces 12.04%~28.68% energy consumption of the CPU with 15.89%~ 41.16% performance losses. We also experiment the potential of method-based design. And we conclude that method-based design is not suitable for embedded JVMs.