Application And Research Of NandFlash In Embedded System

With the broad application of intelligent electronic devices, mobile pocketable devices and various special devices, and the development of the embedded CPUs and the embedded hardware/software technologies, the technologies of embedded system has became a heating research topic. Especially, as the technology of the embedded system has been applied in all kinds of consumed electronic products, the restoring and management of data in the embedded system has become an important research subject. The Flash memorizer is of higher speed, huge capacity, small size, tiny power consumption and lower cost, so it's widely used as assistant memory in the embedded system.The paper analyzes the currents study of NandFlash memory, discuss function characteristic of NandFlash and study the technology of data storage and management in embedded system. NorFlash and NandFlash are two prime non-volatile memorizers in the market now. At first, NandFlash is designed to store data and NorFlash is designed to boot the system and to load read only codes which are accessed with high speed. The paper researched the current bootloader based on embedded system, put forward multi-step booting technique which completes loading from NandFlash. We have also solved the problem of bad block management of storing booting codes on NandFlash and the problem of remapping interrupt vector of multi-step booting.Secondly, this dissertation will discuss the standard reliable FS which is used in the embedded system based on the technique of NandFlash MTD. After pointing out the problems of wear levelling, bad block management and recovery after crash, I will introduce the architecture and the design of the traditional MTD method, and analyze in particular the theory and limitation of the traditional method. At last, I shall provide an improved Banked-Sets MTD method, and explain the theory and improved points of the new Banked-Sets MTD method.According to the characteristics of NandFlash, this article puts forward the strategy of wear leveling based on the heap-sort method, bad block management of remapping address based on block, and recovery after crash of double mapping at writing. The improved method is able to largely reduce the operation of erasing blocks and moving the insignificant data between two different blocks, the two operations requiring a long time to take, especially for MLC NandFlash. Therefore, the improved MTD method will obviously increase the efficiency of accessing data by FS.At last, after completing the designing, implementing, testing, analyzing and comparing the result, we can determine that the improved MTD method is nearly the same as the traditional MTD method in terms of its capacity of accessing big files. However, in the case of writing a large number of small files, the improved MTD method will have an accessing speed about 4 times to 10 times quicker than the traditional MTD method according to the size of the small file. The new MTD method even has a better effect than traditional MTD method in terms of the reading speed.At last there is a summary of this paper, and the future work that will be done is pointed out.