CN103092876A

CN103092876A - Embedded file system based on CF (compact flash)

Info

Publication number: CN103092876A
Application number: CN2011103460639A
Authority: CN
Inventors: 杨际荣
Original assignee: ZHENJIANG HUAYANG INFORMATION TECHNOLOGY CO LTD
Current assignee: ZHENJIANG HUAYANG INFORMATION TECHNOLOGY CO LTD
Priority date: 2011-11-01
Filing date: 2011-11-01
Publication date: 2013-05-08

Abstract

The invention discloses an embedded file system based on a CF (compact flash). The compact flash (called CF for short) is a storage device which is wide in application space and low in cost. The embedded file system comprises an SEP3203 embedded processor and a CF interface circuit, and the operating principle of the CF is used for running a drive program of the CF. An FAT file system is more and more widely applied to the embedded system, a traditional 8.3 format filename cannot meet the requirements of some applications. The difference between a short filename and a long filename is explained, a data structure supporting the long filename is analyzed, and the FAT16 file system is designed and implemented by taking the CF as a storage medium and supports read-write operation of a file with the long filename, so that the problem of difficulty in using the long filename in an embedded environment is effectively solved.

Description

Embedded file system based on the CF card

Technical field

The present invention relates to the embedded file system based on the CF card, the present invention illustrates the difference between short filename and long filenames, analyzed the data structure of supporting long filenames, take CF as the storage medium Design and implementation FAT16 file system. this file system is supported the read-write operation of long filenames file, has effectively solved and has used the existing problem of long filenames under embedded environment.

Background technology

Along with the develop rapidly of electronic technology, computer technology, that embedded system appears at more and more is consumer, in the electronic product of communication class.The development of embedded system requires the system can a large amount of data of store and management.SEP3203 is the embedded microprocessor of a ARM7TDMI of Southeast China University's independent research.SEP3203 mobile terminal application processor is for the application demand of low-cost individual mobile terminal, enriches peripheral hardware, low merit trustship reason and external memory configuration cheaply for what the user provided that facing moving terminal uses.The CF card be specially for mass memory design flash card, have the advantages such as cost is low, compatible good.For the CF card can carry out exchanges data with the Windows system, realize driving file operation based on the CF card with the FAT16 file system.

The FAT file system is used the demand that 8.3 more and more extensive, traditional formatted file names can not meet some application in embedded system.

Summary of the invention

Based on the problems referred to above, hereby invent the embedded file system based on the CF card. this system supports the read-write operation of long filenames file, has effectively solved and has used the existing problem of long filenames under embedded environment.

1.CF card driver design; The write operation of showing disrespect on of CF card is all realized by internal register.The CF card has two groups of internal registers: command register block and control register group.Command register block sends to the disk register and orders and carry out the data exchange, and the control register group is used for controlling disc driver.These two groups of registers are selected by CE1 and CE2.A2 one A0 is the addressed line of register.Select CE1 and CE2 to access each register by address wire A2 one A0 and sheet.When read-write, ide interface has two kinds of working method: LBA (LBA (Logical Block Addressing)) and CHS (cylinder magnetic head/sector).This dual mode is by the 6th digit separator of head register.Under the LBA mode, system hides the sector and can not access, and the sector that can access since 0 cylinder, 0 magnetic head, 1 sector, is No. 0 sector under the LBA mode.All sectors are Unified number successively.During CHS (cylinder P magnetic head P sector) addressing, direct defeated people corresponding cylinder P magnetic head P sector numerical value is just passable.When the LBA access mode, convert the logic sector value that to access to corresponding physical track, cylinder and sector number.The design adopts the LBA addressing.

0, in card read-write operation process, at first arrange and show disrespect on the addressing mode of write access address, then driver/head register, cylinder low byte register, cylinder high byte register, sector number register are set respectively to obtain showing disrespect on the start address of write operation according to set addressing mode.Sector counter then is set decides the data block quantity that to read and write, take piece as unit, the CF card is read and write at last.

2. the design of file system; Numerous Embedded applications relates to showing disrespect on of file and writes, and simultaneously the CF card reader is generally to operate under the Windows system.So must set up a cover file system, the design chooses the FAT16 form, supports long filenames, Chinese file name.

(1) .CF card disk is divided into: boot sector, FAT district, root directory area and data field.Boot sector accounts for 512 bytes, comprises jump instruction, identification of the manufacturer and version number, BPB, expansion BPB and system bootstrap routine.The FAT district is that the FAT file system is used for remembering disk record data field bunch chain structure.Root directory area is used for the information of saving contents.The data of file are preserved in the data field.

Wherein, RS is the reserve sector number, and FS is that the FAT table takies sector number, and NF is FAT table backup number, and acquiescence is that 2, DB is the root directory initial sector, and DS is the root directory number, and SS is the shared byte number in every sector.

(2). the realization of long filenames; The expansion of FAT file system aspect long filenames is called VFAT.Traditional FAT16 file system is only supported the filename of 8.3 forms.The file name list form of 8.3 forms is as shown in table 2.In fact a long filenames is storing two names on catalogue: the another name of a long filenames (short filename) and a long filenames.Short filename as another name is stored in directory entry with 8.3 forms, and long filenames is stored in the attribute mark in several directory entries of OFH.

Wherein, the short name directory entry uses GR2312 code form, and each character needs 1 byte space; The long filenames directory entry uses Unicode code form, so must set up the GB2312 code to the conversion table between the Unicode code.Due in embedding people formula field, only set up the conversion table of 3600 Chinese characters commonly used, usually can satisfy the demand of application.The GB2312 code is regularly arranged, and with the GB2312 code one to one the Unicode code be irregular L6J.So can set up a table according to the rule of GB2312 code.When the GB2312 code is converted to the Unicode code, just can easily obtain side-play amount, when the Unicode code is converted to the GB2312 code, just can only pass through whole table of sequential search.For a long filenames, short filename and long filenames all are stored in directory entry, and the long filenames catalogue is according to the catalogue sequence number storage of first byte.

Wherein, as follows about the judgement whether file exists: judge that first filename is a long filenames, if not, judge according to classic method.If a long filenames is first searched the directory entry of another name (short filename) at directory entry, if do not open unsuccessful.If have, then long filenames synthetic according to the long filenames catalogue, compare with it, if identical, there is this file in explanation, if different, does not exist.After finding directory entry, just can obtain first bunch number of file, realize the read-write operation of file.

The process that creates a new file is: judge that first filename is a long filenames, if not, create according to classic method.If a long filenames, the first enough large space of one of application on directory entry, can deposit another name (short filename) and long filenames, if do not have the space unsuccessfully.Fill in directory entry according to the form of short filename and long filenames again, the backspace file indications.

Claims

1. based on the embedded file system of CF card: this system take CF as the storage medium Design and implementation FAT16 file system.

2. according to claim 1 the embedded file system based on the CF card, this system is mainly operated by the realization of the design of CF card driver, long filenames.The read-write operation of CF card is all realized by internal register.The CF card has two groups of internal registers: command register block and control register group.Command register block sends to the disk register and orders and carry out the data exchange, and the control register group is used for controlling disc driver.The FAT16 form is chosen in the realization design of long filenames, supports long filenames, Chinese file name.