在WinCE上結合壓縮法與SWL改善快閃記憶體磨損平均的方法

Abstract

由於快閃記憶體的寫入特性，儲存資料前必須先抹除(Erase)區塊，所以一般用於傳統硬碟的檔案系統無法直接套用於快閃記憶體；因此若我們希望可以沿用傳統的檔案系統，可藉由使用Translation Layer使檔案系統將快閃記憶體看成一般的傳統硬碟。

在WinCE嵌入式系統中，使用FAL(Flash Abstraction Layer) 與FMD (Flash Media Driver) 的架構，來處理檔案系統與快閃記憶體之間邏輯位址與實體位址的對應、以及實作對快閃記憶體的I/O操作。但缺乏一個有效的方式，避免快閃記憶體區塊磨損不平均的問題。由於區塊抹除有一定的次數(Endurance)，長期抹除某些固定的區塊 (Hot Block)，最終將導致該區塊損毀，並縮短快閃記憶體的使用壽命；因此本篇論文以不修改既有FAL Source Code為前提下，透過新增IFMD (Internal Flash Media Driver)，將磨損平均演算法整合至WinCE FAL與FMD架構中，並在IFMD中針對不常被修改的資料(Cold Data)執行區塊壓縮以產生額外可用的區塊(Hidden Block)輔助SWL(Static Wear Leveling)運作達成快閃記憶體磨損平均(Wear Leveling)且降低SWL執行成本的目的，以維護快閃記憶體的使用壽命。

Because of the writing characteristic of Nand flash memory, it is necessary to erase blocks before writing data. Hence, the file system of hard disk is not appropriate for Nand flash. Transition Layer can take flash memory as normal hard disk for continually using traditional file system.

In WinCE embedded system, Flash Abstraction Layer (FAL) and Flash Media Driver (FMD) are used to map logical address to physical address, and implement the I/O control of flash devices. However, there is no efficient method to avoid the problem of uneven flash blocks erasing. Because of the endurance of block erasing, overly erasing of hot blocks will damage those blocks and reduce the life time of flash devices. Hence, under the premise of not modifying FAL source code, this thesis uses Internal Flash Media Driver (IFMD) to integrate wear leveling algorithm to WinCE FAL and FMD architecture. Compress cold data blocks, which are not often modified, to produce useful hidden blocks for achieving wear leveling, reducing the overhead of SWL, and extending the lifetime of Nand flash memory.