低耗能匯流排編碼方法

Abstract

低耗能眚電設計是目前熱門的研究方向之一，它的好處在於研長電池裝置的壽命、降低晶片的發熱量並減少晶片封裝所需的成本，以及提高電路的穩定性．尤其在嵌入式平台上，由於效能的需求持續增加以應付更多樣的多媒體應用程式。一般而言常使用較寬的外部匯流排。而外部匯流排因其電容質遠大於晶片內部的匯流排因此其所損耗的功率佔了整個系統耗能的50% 至 80%．在匯流排上的耗能。主要來自於狀態的轉換(例如:0-> 1, 1->0)，為此我們提出針對匯流排資料編碼的方式以降低資料在匯流排上傳輸時的狀態改變．在本篇論文中，我們提出了取代連續零位元的編碼方式(Leading Zero Code)，它能利用資料在高位元的部份為正負號研展的特性以前一筆傳輸的資料取代此部份使其在傳輸時不需改變此部份位元的狀態．以及利用遮罩式匯流排編碼方法(Mask-Based Bus Coding Method)並配合匯流排反轉(Bus-Invert)機制，我們利用選定的遮罩與傳輸資料作XOR 運算並配合匯流排反轉以增進匯流排反轉方法的效果．最後我們整合這三種方式以達到更好的效果．實驗結果顯示，新的匯流排編碼方法可以達到平均降低59.3%的位元轉換數的效果，相較於原始的匯流排反轉方法可達到的降低25 %的位元轉換，可以說是一項很大的改進。

Low power design is a more popular research goal. Consider the advantages of low power design. First power reduction can lengthen the life of battery. Second the heat of chip dissipated can be reduced such that package cost is also reduction. Finally the circuit is more reliability. For most embedded systems, we need high performance for various media applications therefore we need the wide system bus to raise the performance of system. However, the external system buses have three orders capacitance of internal bus and the power consumption on external bus is over 50% to 80% of the total system power consumption. Power dissipation on the buses mainly occurs during signal transitions. So we propose an integrated bus coding method to reduce the number of signal transitions. In thesis, we propose a leading zero code which can replace the leading zero bits of current data by the part of last data such that the number of transitions can be reduced. And we propose another mask-based bus coding method and apply bus-invert. We use selected mask to do xor with current data to improve bus-invert coding. Then we integrated these methods to reduce more number of transitions on data bus. For the experimental results, we can improve 59.3% number of bit toggles ratio that is more than 25% number of bit toggles ratio for Bus-Invert Coding.