Research And Improvement Of Nucleus-based Flash File System

Nucleus Plus is a real-time,multi-task and easy-porting embedded operating system,whose flash-based file system is divided into two layers-FAT and FMM.This file system has the advantages of simpleness and easy-porting capability,but it also has some problems while being used.one problem is its week self-repair ability,and the file system breaks down easily when power fails,so the reliability of the file system isn't good enough;The other is that the dirty-sectors-checking procedure takes too much time,which affect the capability of the whole file system.So,it's necessary for us to analyse the whole file system fully and improve it suitably.Aiming at the problems of the file system of Nucleus Plus,we advance it in two views,one is the reliability,the other is the real-timing.First,we find the cause of breaking down easily when power fails by analysing the FAT table and the mechanism of FAT layer.we conclude four performances:cluster-chain cycles,cluster-chain is cited across,the actual file size is different from the value in directory entry and cluster-chain is lost,and improve them one by one.The idiographic work is that we add the function of disk-scanning without changing the whole structure of the source of FAT layer,so the file system can repair itself when error occurs.After the improvement,the source of the file system maintain its independence,so we guarantee its easy-porting capability when improving the reliability.Secondly, we conclude the cause of low efficiency of reclaim dirty sectors by analysing the writing process,erasing process and the algorithm of reclaiming dirty sectors.The cause is that the original algorithm deals with every block one by one.so,we advance and implement choosing algorithm,breaking the regular that the block must be disposed orderly.After the improvement,the real-timing of the file system enhance obviously.the improvement of real-timing still guarantees that most of the writing processes can finish before the capacitance discharges completely,so the probability of breaking down when power fails decreases,which improve the reliability of the file system indirectly.