嵌入式设备中基于NAND Flash的文件系统设计和优化

发布时间：2018-02-03 10:12

本文关键词： 嵌入式文件系统 NAND Flash Cache FAT　出处：《北京交通大学》2013年硕士论文　论文类型：学位论文

【摘要】：处理器技术、存储器技术和软件技术的飞速发展,极大地改变了人们的生活状态,让生活变得更智能,更随心所欲。而嵌入式系统正是集成了这三种技术的产物,加强对嵌入式技术的研究,必将有助于该产业的健康发展,并会给人们生活带来巨大的便利。嵌入式系统包括硬件平台、EOS和嵌入式应用软件。其中硬件平台主要是指嵌入式处理器和存储器,EOS有Linux、Wince、Vworks等,嵌入式应用软件更是种类繁多,不可计数。嵌入式文件系统,是EOS中非常重要的组成部分,它主要负责数据在存储器上的存放、操作和管理,并向用户提供底层的操作接口,使用户不必深入了解底层结构,就能方便操作。嵌入式文件系统与一般的磁盘文件系统结构大致相同,但其有自己的特点。首先,嵌入式设备受系统资源的限制较大,所以嵌入式文件系统必须处理好空间与效率的关系；其次,嵌入式系统一般要求实时性和可靠性,这也是非常重要的；再次,嵌入式文件系统采用的存储器一般是NAND Flash,而NAND Flash由于自身的特点,需要在其和FAT层之间引入FTL层,才能进行类似与磁盘的操作。FTL的主要功能是进行逻辑地址和物理地址间的转换和坏块管理。本文在介绍相关处理器和存储器知识的基础上,为TEE(可信执行环境)系统,设计了一套专用的文件系统,无需考虑与其他系统的兼容性。TEE系统是握奇数据有限公司为手机支付开发的一套安全操作系统,其运行在Android系统上,当需要用手机进行支付时进入该安全环境,本课题是其中一个重要模块。在借鉴FAT32的设计思路和关键技术后,我们设计了一种精简的类FAT文件系统。在文件系统格式上,我们用系统信息区取代了系统引导区,省去了不常用的备用FAT表,仅保留一张FAT表。在功能实现上,也考虑了嵌入式设备资源有限的特点。为了对文件中数据进行更快、更安全的存取,我们在文件系统的FTL层和FAT层之间引入了Cache层。它是FTL进行直接读写的唯一通道,用于提高系统性能以及使系统可以按字节读写某个特定扇区,并对其读写操作进行了实现和优化。我们进一步讨论了Cache性能与命中率的关系,以及影响Cache命中率的因素。
[Abstract]:The rapid development of processor technology, memory technology and software technology has greatly changed people's living conditions and made life more intelligent. The embedded system is the product of the integration of these three technologies. Strengthening the research of embedded technology will help the healthy development of the industry and bring great convenience to people's life. The embedded system includes the hardware platform EOS and embedded application software, in which the hardware platform mainly refers to the embedded processor and memory EOS, such as Linux WinceVworks and so on. Embedded file system is a very important part of EOS, it is mainly responsible for the storage, operation and management of data in memory. And to provide users with the underlying operation interface, so that users do not need to understand the underlying structure, can be convenient to operate. Embedded file system and the general disk file system structure is roughly the same. But it has its own characteristics. Firstly, the embedded device is limited by the system resources, so the embedded file system must deal with the relationship between space and efficiency. Secondly, embedded systems generally require real-time and reliability, which is also very important; Thirdly, the memory used in embedded file system is generally NAND Flash, but NAND Flash needs to introduce FTL layer between FAT layer and NAND Flash because of its own characteristics. The main function of FTL is to translate logical address and physical address and bad block management. Based on the introduction of related processors and memory knowledge, this paper designs a special file system for TEE (trusted execution Environment) system. No need to consider compatibility with other systems. Tee system is a secure operating system for mobile phone payment developed by Juggi data Co., Ltd., which runs on the Android system. This topic is one of the important modules when the payment needs to be paid by mobile phone. After learning from the design ideas and key technologies of FAT32. We design a simplified FAT like file system. In the file system format, we use the system information area instead of the system boot area, eliminating the uncommon standby FAT table. Only one FAT table is retained. In the implementation of the function, the limited resources of embedded devices are also taken into account. In order to access the data in the file faster and more safely. We introduced the Cache layer between the FTL layer and the FAT layer of the file system, which is the only channel for FTL to read and write directly. It is used to improve system performance and enable the system to read and write a particular sector by bytes, and to implement and optimize the read and write operation. We further discuss the relationship between Cache performance and hit rate. And the factors that affect the Cache hit ratio.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TP333;TP316

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