SD卡与fatfs文件系统(1)

    SD的优势之一是它的便携性，它可以自由插拔，可以在嵌入式设备和PC机之间交换数据。如果使用FAT(File Allocation Table)文件系统，它便可以方便在安装windows的PC和嵌入式设备之间交换数据。一个完整的FAT文件系统代码量非常庞大，不适合资源较少的嵌入式系统，于是就需要一个微型的FAT文件系统，FatFs就是基于这样的目的而开发的。

    FatFS是一个专为小型嵌入式系统设计的通用FAT文件系统模块。FatFs具有较高的可配置性，最小配置仅使用1K的RAM空间，非常适用于嵌入式系统。FatFs 的编写遵循ANSI C，并且完全与磁盘I/O层分开。因此，它独立(不依赖)于硬件架构。它可以被嵌入到低成本的微控制器中，如AVR, 8051, PIC, ARM, Z80, 68K 等等，而不需要做任何修改。

特点

• Windows兼容的FAT文件系统
• 不依赖于平台，易于移植
• 代码和工作区占用空间非常小
• 多种配置选项：

多卷(物理驱动器和分区)

多ANSI/OEM代码页，包括DBCS

在ANSI/OEM或Unicode中长文件名的支持

RTOS的支持

多扇区大小的支持

只读，最少API，I/O缓冲区等等

FatFs的源代码只有几个文件:diskio.c,ff.c,ff_util.c,tff.c及头文件。diskio.c是磁盘操作的代码文件(这个文件是移植时要实现的)，ff.c是一般FatFs的代码文件，tff.c是微型FatFs的代码文件，ff_util.c是几个辅助函数。integer.h是内部基本类型的定义，ff.h是一般FatFs包含的头文件，tff.h是微型FatFs包含的头文件。

#if _FATFS_TINY != 1
#include 
#else
#include 
#endif
#include 

微型FatFs配置最小时仅占用内存1KB，但它是一个只读的FAT系统。

FatFs的配置文件是fatfs_config.h:

//------------------------------------------------------------------------------
//      General Definitions (previously in ff.h)
//------------------------------------------------------------------------------

#define	_FATFS_TINY 0
/* When _FATFS_TINY is set to 1, fatfs is compiled in Tiny mode
/ Else, it is compiled in normal mode 
/ Tiny FatFs feature : Very low memory consumption, suitable for small memory 
/ system. (1KB RAM) : Supports only single drive, no disk format, 
/ only read functions, no write functions */

//------------------------------------------------------------------------------
//      Definitions for normal FATFS (previously in ff.h)
//------------------------------------------------------------------------------

#if _FATFS_TINY == 0

#define _MCU_ENDIAN		2
/* The _MCU_ENDIAN defines which access method is used to the FAT structure.
/  1: Enable word access.
/  2: Disable word access and use byte-by-byte access instead.
/  When the architectural byte order of the MCU is big-endian and/or address
/  miss-aligned access results incorrect behavior, the _MCU_ENDIAN must be set to 2.
/  If it is not the case, it can also be set to 1 for good code efficiency. */

#define _FS_READONLY	0
/* Setting _FS_READONLY to 1 defines read only configuration. This removes
/  writing functions, f_write, f_sync, f_unlink, f_mkdir, f_chmod, f_rename,
/  f_truncate and useless f_getfree. */

#define _FS_MINIMIZE	0
/* The _FS_MINIMIZE option defines minimization level to remove some functions.
/  0: Full function.
/  1: f_stat, f_getfree, f_unlink, f_mkdir, f_chmod, f_truncate and f_rename are removed.
/  2: f_opendir and f_readdir are removed in addition to level 1.
/  3: f_lseek is removed in addition to level 2. */

#define	_USE_STRFUNC	0
/* To enable string functions, set _USE_STRFUNC to 1 or 2. */

#define _USE_FSINFO	1
/* To enable FSInfo support on FAT32 volume, set _USE_FSINFO to 1. */

#define	_USE_SJIS	1
/* When _USE_SJIS is set to 1, Shift-JIS code transparency is enabled, otherwise
/  only US-ASCII(7bit) code can be accepted as file/directory name. */

#define	_USE_NTFLAG	1
/* When _USE_NTFLAG is set to 1, upper/lower case of the file name is preserved.
/  Note that the files are always accessed in case insensitive. */

#define	_USE_MKFS	1
/* When _USE_MKFS is set to 1 and _FS_READONLY is set to 0, f_mkfs function is
/  enabled. */

#define _DRIVES		2
/* Number of logical drives to be used. This affects the size of internal table. */

#define	_MULTI_PARTITION	0
/* When _MULTI_PARTITION is set to 0, each logical drive is bound to same
/  physical drive number and can mount only 1st primaly partition. When it is
/  set to 1, each logical drive can mount a partition listed in Drives[]. */

//------------------------------------------------------------------------------
//      Definitions for normal FATFS TINY (previously in tff.h)
//------------------------------------------------------------------------------

#else

#define _MCU_ENDIAN		2
/* The _MCU_ENDIAN defines which access method is used to the FAT structure.
/  1: Enable word access.
/  2: Disable word access and use byte-by-byte access instead.
/  When the architectural byte order of the MCU is big-endian and/or address
/  miss-aligned access results incorrect behavior, the _MCU_ENDIAN must be set to 2.
/  If it is not the case, it can also be set to 1 for good code efficiency. */

#define _FS_READONLY	1
/* Setting _FS_READONLY to 1 defines read only configuration. This removes
/  writing functions, f_write, f_sync, f_unlink, f_mkdir, f_chmod, f_rename,
/  f_truncate, f_getfree and internal writing codes. */

#define _FS_MINIMIZE	0
/* The _FS_MINIMIZE option defines minimization level to remove some functions.
/  0: Full function.
/  1: f_stat, f_getfree, f_unlink, f_mkdir, f_chmod, f_truncate and f_rename are removed.
/  2: f_opendir and f_readdir are removed in addition to level 1.
/  3: f_lseek is removed in addition to level 2. */

#define	_USE_STRFUNC	0
/* To enable string functions, set _USE_STRFUNC to 1 or 2. */

#define _USE_FSINFO	1
/* To enable FSInfo support on FAT32 volume, set _USE_FSINFO to 1. */

#define	_USE_SJIS	1
/* When _USE_SJIS is set to 1, Shift-JIS code transparency is enabled, otherwise
/  only US-ASCII(7bit) code can be accepted as file/directory name. */

#define	_USE_NTFLAG	1
/* When _USE_NTFLAG is set to 1, upper/lower case of the file name is preserved.
/  Note that the files are always accessed in case insensitive. */

#define	_USE_FORWARD	0
/* To enable f_forward function, set _USE_FORWARD to 1. */

#define _FAT32	1
/* To enable FAT32 support in addition of FAT12/16, set _FAT32 to 1. */

#endif

//------------------------------------------------------------------------------
//      Other definitions
//------------------------------------------------------------------------------

/*-----------------------------------------------------------------------*/
/* Correspondence between drive number and physical drive                */
/* Note that Tiny-FatFs supports only single drive and always            */
/* accesses drive number 0.                                              */

#define DRV_MMC          0
#define DRV_SDRAM        1
#define DRV_ATA          2
#define DRV_USB          3


#define SECTOR_SIZE_SDRAM  512
#define SECTOR_SIZE_SDCARD 512