針對嵌入式JPEG編碼之有效記憶體管理

Abstract

目前多媒體應用程式在嵌入式系統上相當熱門，尤其是在像數位相機這樣的消費性電子產品上更是被廣泛地使用。許多研究也因此致力於多媒體應用程式的效能提升上。然而這些研究都需要額外的監測分析工具，特殊的編譯器，或者甚至是修改原始碼。在這篇論文裡，我們在一個小型的作業系統上加入一個記憶體管理層。經由將多媒體應用程式裡最多使用到的資料分類再分別加以處理的方式來提升整體效能。這些資料分為兩大類，分別為靜態和動態資料。對於靜態資料，我們探討其在記憶體當中的位置對快取記憶體效能的影響，以增進整體效能。對於動態資料，我們提出一個新的動態記憶體分配方法，加入對齊資料的觀念，使得上層的應用程式變得更有效率。當系統不允許重新配置快取記憶體的使用區時，我們在 JPEG 上可以得到 5% 效能的改善。而當重新配置快取記憶體之後，我們甚至可以得到 70% 的改善。除此之外，我們實驗在 JBIG 上也達到效能上的提升，可以證實我們的方法適用於其他的編碼上。

Today, multimedia applications are popular in embedded systems, especially the image and video decoders/encoders are widely applied on consumer electronics such as a digital camera. Many researches focus on improving the performance of multimedia applications at source level or system level. However, overheads arise as modifying source codes, using profiling tools, or requiring specific compilers/precompilers in these researches. In this thesis, we add a memory manager to an embedded operating system $mu$C/OS-II. The memory manager deals with the most data in a multimedia application, and classifies the data into two types: statically allocated data and temporary data. For statically allocated data, the data locations in the memory are considered to enhance the data cache usage. For temporary data, we present a new and flexible dynamic memory manager to align the temporary data on cache lines such that the multimedia applications would be more efficient. Experiments on JPEG encoder illustrate that we are able to reduce up to 5 percent of the execution time when the system does not allow reconfiguring the data cache, and 70 percent of the execution time after reconfiguring the data cache. Furthermore, experiments on JBIG encoder show the similar enhancement which implies that the memory manager is also practical for other encoders.