Research And Implementation Of Flash Algorithm Based On SD3.0 Controller

SD memory card is a new generation of high-capacity mobile storage device,which has the advantages of fast read and write,small size and data security.It is widely used in electronic products such as MP3,MP4 and digital cameras.Most SD cards use NAND Flash as the storage medium.The operating system can not access NAND Flash directly,in order to solve this problem,FTL(Flash Translation Layer)is added between the operating system and NAND Flash.NAND Flash is modeled as a normal disk by FTL,so that the operating system can operate the SD card's IO like a normal disk.FTL algorithm is the core technology of SD card storage system,its performance is directly related to the pros and cons of the product.This paper designs an improved DFTL algorithm based on second level cache.This paper first introduced the structure of SD card,inic-2051 master chip,NAND Flash chip and functions of FTL algorithm.Then,several address mapping strategies are analyzed in detail,and based on the DFTL strategy,an improved FTL algorithm is proposed.The FTL algorithm designed in this paper includes address mapping system,garbage collection system,bad block management system and power-on recovery system and it is implemented by firmware on the SD card.For the address mapping strategy,Cache Mapping Table,Global Mapping Table and Global Translation Directory are designed to find the address.Second level cache is added to find address,which not only increases the hit rate of the addressing,but also reduces the number of times index tables are written back.The garbage collection system proposes the concept of ERCT and adopts a combination of voluntary combination and passive combination,it not only recovers physical blocks which has the largest number of invalid pages,but also balances wear leveling.Bad block management system uses the combination of factory bad block scanning and dynamic bad block scanning.ECC and Read Retry are used to correct data errors and prolong the life of dynamic bad blocks.The power-on recovery system is used to accurately restore index tables in memory during power-off.By copying two index tables in NAND Flash,it not only ensures the recovery of index tables during abnormal power-down,but also ensures the reliability and stabilityof the SD card.Finally,the algorithm is implemented in the form of firmware to the SD card,the test results show that SD card data transmission is stable and reliable and the speed is considerable.