Based On Embedded Nand Flash File System

Traditional embedded system is mainly applied in industry control area which doesn't request to store a lot data, so file system is not a necessary component in embedded system. Along embedded technology is adopted widely in the area of aeronautic electronics, auto electronics, and consumer electronics and so on, data store and management has become very important, and embedded file system has emerged gradually.Embedded system has its own specific characteristics: small size, shock resistance, and low power consumption. Disk can not satisfy these reqirements, it is not appropriate to store data. Flash is a new kind of memory which is using as external storage in embedded system, because it is low cost, large capacity, small size, low power consumption. Compared to disk, it is superior.In recent year, some file syetems have been developed specially for Flash memory. They come into three flavors: embedded file system based on block device, universal flash file system and specific flash file system. The first type is trodational file system based on block device which is transplant to flash memory. The second type is designed for flash memory specifically. It can run on NOR flash and NAND flash, so it is universal. The last type is specific file system, only designed for NAND flash. They present the three stages the flash file system progresses. Althought flash file sytem is becoming better and better, there are a lot of shortcoming existing, such as too long starting time, high comsuption of main memory, and insufficient consideration of wear leveling.Aiming at the shortcomings about NAND flash file system, this paper proposes some methods to solve them. Current NAND flash file system store file attribute information and data information in the same block of flash, then the system has to scan all block of flash to get the information about file attribute. About this item, this paper changes the management way to store the two kind of file information in different block. When system start up, only blocks which store attribute information need to be scan. This way would reduce the starting time. Curren flash file systems consume a lot of main memory to store the structure of all files in flash. According to the program local principle, this paper only stores the information about files which are accessed recently. This way can reduce the consumption of main memory significantly. Current file systems, for example YAFFS, do not consider the wear level among flash blocks sufficiently, this paper will solve this problem through using the idea of hot and cold data.Using the above method, a new NAND Flash file system SFFS is implemented. The test result indicate the performance of SFFS is a lot better than current NAND Flash file system YAFFS.