目录
1. FatFs文件系统简介
简而言之，文件系统即为，在存储设备上组织文件的方法。常见的windows下的文件系统格式包括FAT32、NTFS、exFAT。在使用文件系统前，要先对存储介质进行格式化。格式化先擦除原来内容，在存储介质上新建一个文件分配表和目录。这样，文件系统就可以记录数据存放的物理地址，剩余空间。
FatFs是面向小型嵌入式系统的一种通用的FAT文件系统。它完全是由AISI C语言编写并且完全独立于底层的I/O介质。因此它可以很容易地不加修改地移植到其他的处理器当中，如8051、PIC、AVR、SH、Z80、H8、ARM等。FatFs支持FAT12、FAT16、FAT32等格式。
官方文档及源码可以从FatFs官网获取：
http://elm-chan.org/fsw/ff/00index_e.html
以下皆以最新的R0.13c版本移植。
1.1 FatFs的目录结构
FatFs的官网获取源码，最新版本为R0.13c，解压之后可看到里面有 documents和 source 这两个文件夹。
1.2 FatFs帮助文档
打开 documents文件夹
其中,doc 这两个文件夹里面是编译好的html文档，讲的是FATFS里面各个函数的使用方法; res 需要用到的图片。
00index_e.html 直接打开，可以看到系统简介，及相关API的介绍，具体链接doc的相关函数介绍文档。
1.3 FatFs源码
打开 source 文件夹
- 00readme.txt This file.
- 00history.txt 版本历史
- ff.c FatFs核心文件，文件管理的实现方法。该文件独立于底层介质操作文件的函数，利用这些函数实现文件的读写。
- ffconf.h FatFs功能配置的宏定义，可以根据需要裁剪其功能
- ff.h FatFs和应用程序模块的通用包含文件。
- diskio.h FatFs和磁盘I / O模块的公共包含文件。
- diskio.c 包含底层存储介质的操作函数，这些函数需要用户自己实现，主要添加底层驱动函数。
- ffunicode.c 可选的Unicode实用程序功能
- ffsystem.c 可选的O / S相关功能的。
文件阅读顺序 diskio.c --> ff.c，阅读文件系统源码ff.c文件需要一定的功底，建议读者先阅读FAT32的文件格式，再去分析ff.c文件。
2. FatFs 文件系统的移植
2.1 FatFs 分层体系
用户应用程序需要由用户编写，一般我们只用到f_mount()、f_open()、f_write()、f_read()就可以实现文件的读写操作.
FatFs组件是FatFs的主体，文件都在源码src文件夹中，其中ff.c、ff.h、ffunicode.c.以及diskio.h四个文件我们不需要改动，只需要修改ffconf.h和diskio.c两个文件，根据是否有操作系统修改ffsystem.c。
2.1 FatFs 移植步骤
在此以秉火429 SPI Flash芯片作为物理存储设备，驱动具体驱动不做赘述，具体见链接
https://blog.csdn.net/XieWinter/article/details/95077050
2.1.1 添加 FatFs 源码到工程
源码直接解压拷贝，添加到工程，并包含相关的H文件。因为未使用到操作系统，所以屏蔽掉了ffsystem.c，如下图：
如果直接编译会发现会出错，因此需要修改diskio.c，系统默认使用日语，需要支持中文的话需要修改ffconf.h，当然，相关的裁剪根据需要，配置ffconf.h相关的宏。
配置ffconf.h，宏定义对应的功能，代码中都有说明，具体的配置范围可以见官方配置说明
http://elm-chan.org/fsw/ff/doc/config.html
具体配置，可以通过对比软件来查看与官方源码的差异点，这样有助于理解。
/*---------------------------------------------------------------------------/
/ FatFs Functional Configurations
/---------------------------------------------------------------------------*/
#define FFCONF_DEF 86604 /* Revision ID */
/*---------------------------------------------------------------------------/
/ Function Configurations
/---------------------------------------------------------------------------*/
#define FF_FS_READONLY 0
/* 此选项可切换只读配置,默认为可读写（0）. (0:Read/Write or 1:Read-only)
/ Read-only configuration removes writing API functions, f_write(), f_sync(),
/ f_unlink(), f_mkdir(), f_chmod(), f_rename(), f_truncate(), f_getfree()
/ and optional writing functions as well. */
#define FF_FS_MINIMIZE 0
/* 此选项定义最小化级别以删除一些基本API函数。
/
/ 0: Basic functions are fully enabled.
/ 1: f_stat(), f_getfree(), f_unlink(), f_mkdir(), f_truncate() and f_rename()
/ are removed.
/ 2: f_opendir(), f_readdir() and f_closedir() are removed in addition to 1.
/ 3: f_lseek() function is removed in addition to 2. */
#define FF_USE_STRFUNC 0
/* 此选项切换字符串函数, f_gets(), f_putc(), f_puts() and f_printf().
/ 如果工作在windows下，为保证文件兼容性(如换行符’\n’和回车符’\r’)建议将此项设置为2
/
/ 0: Disable string functions.
/ 1: Enable without LF-CRLF conversion.
/ 2: Enable with LF-CRLF conversion. */
#define FF_USE_FIND 0
/* 此选项可切换筛选的目录读取功能, f_findfirst() and
/ f_findnext(). (0:Disable, 1:Enable 2:Enable with matching altname[] too) */
/* 用于搜索文件夹相关的文件 */
#define FF_USE_MKFS 1
/* 此选项可切换f_mkfs（）函数。 (0:Disable or 1:Enable) */
#define FF_USE_FASTSEEK 0
/* 此选项可切换快速搜索功能. (0:Disable or 1:Enable) */
/* 开启后，会使用FIL结构体中的cltbl元素来加快搜索 */
#define FF_USE_EXPAND 0
/* 此选项可切换f_expand函数 (0:Disable or 1:Enable) */
/* 文件准备或分配连续的数据区域。 */
#define FF_USE_CHMOD 0
/* 此选项可切换属性操作功能, f_chmod() and f_utime().
/ (0:Disable or 1:Enable) Also FF_FS_READONLY needs to be 0 to enable this option. */
#define FF_USE_LABEL 0
/* 此选项可切换卷标功能, f_getlabel() and f_setlabel().
/ (0:Disable or 1:Enable) */
#define FF_USE_FORWARD 0
/* 此选项可切换 f_forward() 功能. (0:Disable or 1:Enable) */
/* 数据立即转存到数据流中，以节省RAM空间 */
/*---------------------------------------------------------------------------/
/ Locale and Namespace Configurations
/ 区域设置和命名空间配置
/---------------------------------------------------------------------------*/
#define FF_CODE_PAGE 936
/* This option specifies the OEM（Original Equipment Manufacture） code page to be used on the target system.
/ 此选项指定目标系统上使用的OEM代码页。代码页是字符集编码的别称，亦称内码表。
/ Incorrect code page setting can cause a file open failure.
/ 代码页设置不正确可能导致文件打开失败。
/
/ 437 - U.S.
/ 720 - Arabic
/ 737 - Greek
/ 771 - KBL
/ 775 - Baltic
/ 850 - Latin 1
/ 852 - Latin 2
/ 855 - Cyrillic
/ 857 - Turkish
/ 860 - Portuguese
/ 861 - Icelandic
/ 862 - Hebrew
/ 863 - Canadian French
/ 864 - Arabic
/ 865 - Nordic
/ 866 - Russian
/ 869 - Greek 2
/ 932 - Japanese (DBCS)
/ 936 - Simplified Chinese (DBCS)
/ 949 - Korean (DBCS)
/ 950 - Traditional Chinese (DBCS)
/ 0 - Include all code pages above and configured by f_setcp()
*/
/* OEM是什么意思呢？在OS编码中，unicode是一种双字节字符编码，无论中文还是英文，或者其他语言统一到2个字节，
/ 它与现有的任何编码（ASCII，GB等）都不兼容。WindowsNT(2000)的内核即使用该编码，所有数据进入内核前转换成UNICODE，
/ 退出内核后在转换成版本相关的编码（通常称为OEM，在简体中文版下即为GB)；*/
#define FF_USE_LFN 2
#define FF_MAX_LFN 255 // 可存储长文件的最大长度
/* The FF_USE_LFN switches the support for LFN (long file name).
/ 主要用于长文件名的支持及缓冲区的动态分配
/
/ 0: Disable LFN. FF_MAX_LFN has no effect.( 不支持长文件名)
/ 1: Enable LFN with static working buffer on the BSS. Always NOT thread-safe.(支持长文件名存储的静态分配，一般是存储在BSS 段)
/ 2: Enable LFN with dynamic working buffer on the STACK. (支持长文件名存储的动态分配，存储在栈上)
/ 3: Enable LFN with dynamic working buffer on the HEAP. (支持长文件名存储的动态分配，存储在堆上)
/
/ To enable the LFN, ffunicode.c needs to be added to the project. The LFN function
/ requiers certain internal working buffer occupies (FF_MAX_LFN + 1) * 2 bytes and
/ additional (FF_MAX_LFN + 44) / 15 * 32 bytes when exFAT is enabled.
/ The FF_MAX_LFN defines size of the working buffer in UTF-16 code unit and it can
/ be in range of 12 to 255. It is recommended to be set 255 to fully support LFN
/ specification.
/ When use stack for the working buffer, take care on stack overflow. When use heap
/ memory for the working buffer, memory management functions, ff_memalloc() and
/ ff_memfree() in ffsystem.c, need to be added to the project. */
#define FF_LFN_UNICODE 0
/* This option switches the character encoding on the API when LFN is enabled.
/ 启用LFN时，此选项可在API上切换字符编码。
/
/ 0: ANSI/OEM in current CP (TCHAR = char)
/ 1: Unicode in UTF-16 (TCHAR = WCHAR)
/ 2: Unicode in UTF-8 (TCHAR = char)
/ 3: Unicode in UTF-32 (TCHAR = DWORD)
/
/ Also behavior of string I/O functions will be affected by this option.
/ When LFN is not enabled, this option has no effect. */
#define FF_LFN_BUF 255
#define FF_SFN_BUF 12
/* 这组选项定义FILINFO结构中文件名成员的大小，用于读出目录项 */
/* This set of options defines size of file name members in the FILINFO structure
/ which is used to read out directory items. These values should be suffcient for
/ the file names to read. The maximum possible length of the read file name depends
/ on character encoding. When LFN is not enabled, these options have no effect. */
#define FF_STRF_ENCODE 3
/* When FF_LFN_UNICODE >= 1 with LFN enabled, string I/O functions, f_gets(),
/ f_putc(), f_puts and f_printf() convert the character encoding in it.
/ This option selects assumption of character encoding ON THE FILE to be
/ read/written via those functions.
/
/ 0: ANSI/OEM in current CP
/ 1: Unicode in UTF-16LE
/ 2: Unicode in UTF-16BE
/ 3: Unicode in UTF-8
*/
#define FF_FS_RPATH 0
/* This option configures support for relative path.
/ 配置相对路径函数
/
/ 0: Disable relative path and remove related functions.
/ 1: Enable relative path. f_chdir() and f_chdrive() are available.
/ 2: f_getcwd() function is available in addition to 1.
*/
/*---------------------------------------------------------------------------/
/ Drive/Volume Configurations
/ 驱动器/卷配置
/---------------------------------------------------------------------------*/
#define FF_VOLUMES 2
/* Number of volumes (logical drives) to be used. (1-10) */
/* 支持的逻辑设备数目 */
#define FF_STR_VOLUME_ID 0
/* 使能或禁用字符串卷标识。要使能字符串卷标识，需要预先定义标识字符串，使用宏_VOLUME_STRS定义。
/ 0 Only DOS/Windows style drive prefix in numeric ID can be used. 0:/filename
/ 1 Also DOS/Windows style drive prefix in string ID can be used. flash:/filename
/ 2 Also Unix style drive prefix in string ID can be used. /flash/filename
*/
#define FF_VOLUME_STRS "RAM","NAND","CF","SD","SD2","USB","USB2","USB3"
/* FF_STR_VOLUME_ID switches support for volume ID in arbitrary strings.
/ When FF_STR_VOLUME_ID is set to 1 or 2, arbitrary strings can be used as drive
/ number in the path name. FF_VOLUME_STRS defines the volume ID strings for each
/ logical drives. Number of items must not be less than FF_VOLUMES. Valid
/ characters for the volume ID strings are A-Z, a-z and 0-9, however, they are
/ compared in case-insensitive. If FF_STR_VOLUME_ID >= 1 and FF_VOLUME_STRS is
/ not defined, a user defined volume string table needs to be defined as:
/
/ const char* VolumeStr[FF_VOLUMES] = {"ram","flash","sd","usb",...
*/
#define FF_MULTI_PARTITION 0
/* This option switches support for multiple volumes on the physical drive.
/ By default (0), each logical drive number is bound to the same physical drive
/ number and only an FAT volume found on the physical drive will be mounted.
/ When this function is enabled (1), each logical drive number can be bound to
/ arbitrary physical drive and partition listed in the VolToPart[]. Also f_fdisk()
/ funciton will be available. */
#define FF_MIN_SS 512
#define FF_MAX_SS 4096
/* 配置扇区大小
/ 当_MAX_SS > _MIN_SS，FatFs被配置为扇区大小可变的并且必须在函数disk_ioctl中实现GET_SECTOR_SIZE命令*/
/* This set of options configures the range of sector size to be supported. (512,
/ 1024, 2048 or 4096) Always set both 512 for most systems, generic memory card and
/ harddisk. But a larger value may be required for on-board flash memory and some
/ type of optical media. When FF_MAX_SS is larger than FF_MIN_SS, FatFs is configured
/ for variable sector size mode and disk_ioctl() function needs to implement
/ GET_SECTOR_SIZE command. */
#define FF_USE_TRIM 0
/* This option switches support for ATA-TRIM. (0:Disable or 1:Enable)
/ To enable Trim function, also CTRL_TRIM command should be implemented to the
/ disk_ioctl() function. */
#define FF_FS_NOFSINFO 0
/* If you need to know correct free space on the FAT32 volume, set bit 0 of this
/ option, and f_getfree() function at first time after volume mount will force
/ a full FAT scan. Bit 1 controls the use of last allocated cluster number.
/
/ bit0=0: Use free cluster count in the FSINFO if available.
/ bit0=1: Do not trust free cluster count in the FSINFO.
/ bit1=0: Use last allocated cluster number in the FSINFO if available.
/ bit1=1: Do not trust last allocated cluster number in the FSINFO.
*/
/*---------------------------------------------------------------------------/
/ System Configurations
/ 系统配置
/---------------------------------------------------------------------------*/
#define FF_FS_TINY 0
/* This option switches tiny buffer configuration. (0:Normal or 1:Tiny)
/ At the tiny configuration, size of file object (FIL) is shrinked FF_MAX_SS bytes.
/ Instead of private sector buffer eliminated from the file object, common sector
/ buffer in the filesystem object (FATFS) is used for the file data transfer. */
#define FF_FS_EXFAT 0
/* EXFAT 文件系统支持 */
/* This option switches support for exFAT filesystem. (0:Disable or 1:Enable)
/ To enable exFAT, also LFN needs to be enabled. (FF_USE_LFN >= 1)
/ Note that enabling exFAT discards ANSI C (C89) compatibility. */
#define FF_FS_NORTC 0
#define FF_NORTC_MON 1
#define FF_NORTC_MDAY 1
#define FF_NORTC_YEAR 2020
/* 时间戳配置，使用RTC需要实现 get_fattime()函数 */
/* The option FF_FS_NORTC switches timestamp functiton. If the system does not have
/ any RTC function or valid timestamp is not needed, set FF_FS_NORTC = 1 to disable
/ the timestamp function. Every object modified by FatFs will have a fixed timestamp
/ defined by FF_NORTC_MON, FF_NORTC_MDAY and FF_NORTC_YEAR in local time.
/ To enable timestamp function (FF_FS_NORTC = 0), get_fattime() function need to be
/ added to the project to read current time form real-time clock. FF_NORTC_MON,
/ FF_NORTC_MDAY and FF_NORTC_YEAR have no effect.
/ These options have no effect at read-only configuration (FF_FS_READONLY = 1). */
#define FF_FS_LOCK 0
/* 选项FF_FS_LOCK切换文件锁定功能，以控制打开对象的重复文件打开和非法操作 */
/* The option FF_FS_LOCK switches file lock function to control duplicated file open
/ and illegal operation to open objects. This option must be 0 when FF_FS_READONLY
/ is 1.
/
/ 0: Disable file lock function. To avoid volume corruption, application program
/ should avoid illegal open, remove and rename to the open objects.
/ >0: Enable file lock function. The value defines how many files/sub-directories
/ can be opened simultaneously under file lock control. Note that the file
/ lock control is independent of re-entrancy. */
/* #include <somertos.h> // O/S definitions */
#define FF_FS_REENTRANT 0
#define FF_FS_TIMEOUT 1000
#define FF_SYNC_t HANDLE
/* 选项FF_FS_REENTRANT切换FatFs模块本身的重入（线程安全）。
/ 请注意，无论此选项如何，对不同卷的文件访问始终是可重入的，并且卷控制函数f_mount（），
/ f_mkfs（）和f_fdisk（）函数始终不可重入。 只有对同一卷的文件/目录访问权限才能受此功能的控制。*/
/* The option FF_FS_REENTRANT switches the re-entrancy (thread safe) of the FatFs
/ module itself. Note that regardless of this option, file access to different
/ volume is always re-entrant and volume control functions, f_mount(), f_mkfs()
/ and f_fdisk() function, are always not re-entrant. Only file/directory access
/ to the same volume is under control of this function.
/
/ 0: Disable re-entrancy. FF_FS_TIMEOUT and FF_SYNC_t have no effect.
/ 1: Enable re-entrancy. Also user provided synchronization handlers,
/ ff_req_grant(), ff_rel_grant(), ff_del_syncobj() and ff_cre_syncobj()
/ function, must be added to the project. Samples are available in
/ ffsystem.c.
/
/ The FF_FS_TIMEOUT defines timeout period in unit of time tick.
/ The FF_SYNC_t defines O/S dependent sync object type. e.g. HANDLE, ID, OS_EVENT*,
/ SemaphoreHandle_t and etc. A header file for O/S definitions needs to be
/ included somewhere in the scope of ff.h. */
/*--- End of configuration options ---*/
/*-----------------------------------------------------------------------*/
/* Low level disk I/O module skeleton for FatFs (C)ChaN, 2016 */
/*-----------------------------------------------------------------------*/
/* If a working storage control module is available, it should be */
/* attached to the FatFs via a glue function rather than modifying it. */
/* This is an example of glue functions to attach various exsisting */
/* storage control modules to the FatFs module with a defined API. */
/*-----------------------------------------------------------------------*/
#include "ff.h" /* Obtains integer types */
#include "diskio.h" /* Declarations of disk functions */
#include "flash/bsp_spi_flash.h"
/* Definitions of physical drive number for each drive */
#define DEV_MMC 0 /* Example: Map MMC/SD to physical drive 0 */
#define DEV_EX_FLASH 1 /* Example: Map SPI FLASH card to physical drive 1 */
#define DEV_USB 2 /* Example: Map USB MSD to physical drive 2 */
/*-----------------------------------------------------------------------*/
/* Get Drive Status (获取磁盘状态) */
/*-----------------------------------------------------------------------*/
DSTATUS disk_status (
BYTE pdrv /* Physical drive nmuber to identify the drive */
)
{
DSTATUS stat;
// int result;
switch (pdrv) {
case DEV_EX_FLASH :
// result = RAM_disk_status();
if (sFLASH_ID == SPI_FLASH_ReadID()) {
stat = RES_OK;
} else {
stat = STA_NOINIT;
}
return stat;
case DEV_MMC :
// result = MMC_disk_status();
// translate the reslut code here
stat = RES_OK;
return stat;
case DEV_USB :
// result = USB_disk_status();
// translate the reslut code here
stat = RES_OK;
return stat;
}
return STA_NOINIT;
}
/*-----------------------------------------------------------------------*/
/* Inidialize a Drive */
/*-----------------------------------------------------------------------*/
DSTATUS disk_initialize (
BYTE pdrv /* Physical drive nmuber to identify the drive */
)
{
DSTATUS stat=STA_NOINIT;
// int result;
switch (pdrv) {
case DEV_EX_FLASH : {
uint16_t i;
/* 初始化 */
SPI_FLASH_Init ();
/* 延时一小会 */
i=500;
while(--i);
/* 唤醒 FLASH */
SPI_Flash_WAKEUP ();
/* 检查状态 */
stat = disk_status(pdrv);
return stat;
}
case DEV_MMC :
// result = MMC_disk_initialize();
// translate the reslut code here
return stat;
case DEV_USB :
// result = USB_disk_initialize();
// translate the reslut code here
return stat;
}
return STA_NOINIT;
}
/*-----------------------------------------------------------------------*/
/* Read Sector(s) */
/*-----------------------------------------------------------------------*/
DRESULT disk_read (
BYTE pdrv, /* Physical drive nmuber to identify the drive */
BYTE *buff, /* Data buffer to store read data */
DWORD sector, /* Start sector in LBA */
UINT count /* Number of sectors to read */
)
{
DRESULT res=RES_PARERR;
// int result;
switch (pdrv) {
case DEV_EX_FLASH : {
/* 初始位置偏移6M */
sector+=1536;
SPI_FLASH_BufferRead(buff, (sector*SPI_FLASH_SECTOR_SIZE), (count*SPI_FLASH_SECTOR_SIZE));
res = RES_OK;
}
return res;
case DEV_MMC :
// translate the arguments here
// result = MMC_disk_read(buff, sector, count);
// translate the reslut code here
return res;
case DEV_USB :
// translate the arguments here
// result = USB_disk_read(buff, sector, count);
// translate the reslut code here
return res;
}
return RES_PARERR;
}
/*-----------------------------------------------------------------------*/
/* Write Sector(s) */
/*-----------------------------------------------------------------------*/
#if FF_FS_READONLY == 0
DRESULT disk_write (
BYTE pdrv, /* Physical drive nmuber to identify the drive */
const BYTE *buff, /* Data to be written */
DWORD sector, /* Start sector in LBA */
UINT count /* Number of sectors to write */
)
{
DRESULT res=RES_PARERR;
// int result;
switch (pdrv) {
case DEV_EX_FLASH : {
uint32_t write_addr;
sector +=1536;
write_addr = (sector*SPI_FLASH_SECTOR_SIZE);
SPI_FLASH_SectorErase(write_addr);
SPI_FLASH_BufferWrite((u8 *)buff,write_addr,(count*SPI_FLASH_SECTOR_SIZE));
res = RES_OK;
}
return res;
case DEV_MMC :
// translate the arguments here
// result = MMC_disk_write(buff, sector, count);
// translate the reslut code here
return res;
case DEV_USB :
// translate the arguments here
// result = USB_disk_write(buff, sector, count);
// translate the reslut code here
return res;
}
return RES_PARERR;
}
#endif
/*-----------------------------------------------------------------------*/
/* Miscellaneous Functions */
/*-----------------------------------------------------------------------*/
DRESULT disk_ioctl (
BYTE pdrv, /* Physical drive nmuber (0..) */
BYTE cmd, /* Control code */
void *buff /* Buffer to send/receive control data */
)
{
DRESULT res;
int result;
switch (pdrv) {
case DEV_EX_FLASH : {
switch (cmd) {
/* 扇区数量：2560*4096/1024/1024=10(MB) */
case GET_SECTOR_COUNT:
*(DWORD * )buff = 2560;
break;
/* 扇区大小 */
case GET_SECTOR_SIZE :
*(WORD * )buff = SPI_FLASH_SECTOR_SIZE;
break;
/* 同时擦除扇区个数 */
case GET_BLOCK_SIZE :
*(DWORD * )buff = 1;
break;
}
res = RES_OK;
}
return res;
case DEV_MMC :
// Process of the command for the MMC/SD card
return res;
case DEV_USB :
// Process of the command the USB drive
return res;
}
return RES_PARERR;
}
__weak DWORD get_fattime(void) {
/* 返回当前时间戳 */
return ((DWORD)(2020 - 1980) << 25) /* Year 2020 */
| ((DWORD)1 << 21) /* Month 1 */
| ((DWORD)1 << 16) /* Mday 1 */
| ((DWORD)0 << 11) /* Hour 0 */
| ((DWORD)0 << 5) /* Min 0 */
| ((DWORD)0 >> 1); /* Sec 0 */
}
2.2 FatFs主要功能配置点
ffconf.h文件是FatFs功能配置文件，根据需要来裁剪，已到达高效实用设备资源的目的。
- #define FF_USE_MKFS 1
格式化功能选择，为使用FatFs格式化功能，需要配置为1
- #define FF_CODE_PAGE 936
语言功能选择，并要求把相关语言文件添加到工程宏。为支持简体中文文件名需要使用“936”，编码文件ffunicode.c需要添加
- #define FF_USE_LFN 2
长文件名支持，默认不支持长文件名，这里配置为2，支持长文件名，并指定使用栈空间为缓冲区。
- #define FF_VOLUMES 2
指定物理设备数量，这里设置为2，包括预留SD卡和SPI Flash芯片。
- #define FF_STR_VOLUME_ID 0
使能或禁用字符串卷标识，可以实现DOS/Windows style或Unix style文件或路径格式
- #define FF_MIN_SS 512
- #define FF_MAX_SS 4096
指定扇区大小的最小值和最大值。SD卡扇区大小一般都为512字节，SPI Flash芯片扇区大小一般设置为4096字节，所以需要把_MAX_SS改为4096。
- #define FF_FS_NORTC 0
时间戳配置，使用时间戳的话，需要实现get_fattime()并关联硬件RTC
- #define FF_FS_REENTRANT 0
可重入，用于有操作系统的时候；使用该功能，需要实现ffsystem.c中的相关函数；前后台模式，则不需要关系。
3. FatFs模块应用说明
官方应用说明，理解该文档，基本大多数的疑问都可以得到解答
http://elm-chan.org/fsw/ff/doc/appnote.html
4. FatFs 文件系统的缺点
- 无掉电保护，异常掉电会损坏文件系统
- 不支持负载均衡
在许多物联网使用案例中，需要具有电源丢失弹性，数据完整性和更长的存储器使用寿命，littlefs以其更加优秀的性能提供更好的体验，后续将详解。源码链接https://github.com/ARMmbed/littlefs