嵌入式MCU文件系统技术分享：从选型到FatFS深度应用

嵌入式MCU文件系统技术分享：从选型到FatFS深度应用

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嵌入式文件系统概述

在嵌入式MCU开发中，文件系统提供了对存储介质的抽象管理，使得应用程序可以像在PC上一样通过文件、目录等概念来组织数据，而无需关心底层存储的具体物理特性。

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一、为什么需要文件系统？

数据管理规范化：提供标准化的API接口（open、read、write、seek等）

增强可靠性：具备断电保护机制，防止数据损坏或丢失

延长存储寿命：通过磨损均衡技术平均分配Flash写入操作

支持复杂结构：能够保存日志、配置备份等结构化数据

跨平台兼容：便于与PC或其他系统进行数据交换

二、嵌入式存储介质类型

介质类型	特点	典型应用
NOR Flash	随机访问快、写入慢、擦除块大	代码存储、小容量数据
NAND Flash	顺序访问快、容量大、有坏块	大容量数据存储
SD/TF卡	容量大、可移动、兼容性好	据记录、扩展存储
eMMC	集成控制器、高可靠性	嵌入式大容量存储
SPI Flash	接口简单、成本低、容量小	参数存储、日志记录

三、各类文件系统深度比较

嵌入式文件系统分类

通用型文件系统
FAT/FatFS：兼容性好，适合与PC交换数据
ext2/3/4：Linux标准文件系统，功能完善

专用型文件系统
LittleFS：为嵌入式Flash设计，断电安全
SPIFFS：针对SPI Flash优化的小型文件系统
YAFFS2：专为NAND Flash设计

轻量型文件系统
NVS (Non-Volatile Storage)：键值对存储，简单高效
EEPROM模拟：将Flash模拟为EEPROM使用

文件系统对比

文件系统	技术特点	最佳适用场景	性能特点	资源占用
LittleFS	日志结构、写时复制、磨损均衡	嵌入式Flash、参数存储	小文件读写优，随机访问好	RAM: 1-4KB, ROM: 10-20KB
FatFS	FAT兼容、通用性强、可配置	SD卡、通用存储、跨平台	平衡性好，顺序读写佳	RAM: 0.7-2KB, ROM: 10-30KB
SPIFFS	针对SPI Flash、磨损均衡	SPI NOR Flash、小容量存储	小文件性能好，垃圾回收有延迟	RAM: 1-2KB, ROM: 8-15KB
NVS	键值对、简单安全、断电保护	结构化配置数据存储	读写速度快，适合小数据	RAM: <1KB, ROM: 5-10KB
JFFS2	日志结构、压缩、Linux原生	NOR Flash、Linux系统	可靠性高，占用CPU资源多	RAM: 10-100KB, ROM: 50-100KB
ext2/3/4	Linux标准、功能完善	eMMC、大容量存储	性能好，功能丰富	RAM: 10-50KB, ROM: 50-200KB

选择考量因素

存储介质特性
NOR Flash：擦除块大，适合LittleFS等
NAND Flash：需要坏块管理，适合YAFFS2
SD卡：标准块设备，适合FatFS

数据特性
小文件多：LittleFS、SPIFFS
大文件多：FatFS、ext2
键值对：NVS

资源限制
RAM有限：NVS、SPIFFS
ROM有限：LittleFS、FatFS精简配置

可靠性要求
高可靠性：LittleFS、JFFS2
一般需求：FatFS、SPIFFS

功能需求
长文件名：FatFS(需配置)
权限控制：ext2/3/4
压缩：JFFS2

FatFS文件系统解析

FatFS采用分层架构设计，从上到下分为：

应用层：用户调用文件API接口
FatFS核心层：实现FAT文件系统逻辑
磁盘I/O层：提供底层存储介质访问
物理层：具体存储硬件驱动

+--------------------------------+
|          应用程序              |
+--------------------------------+
|          FatFS核心             |
| (ff.c, ff.h, ffconf.h)         |
+--------------------------------+
|          磁盘I/O层             |
| (diskio.c, diskio.h)           |
+--------------------------------+
|          物理驱动层            |
| (sd_diskio.c, spi_flash.c)     |
+--------------------------------+

FatFS特点与优势

1. 平台无关性：易于移植到各种微控制器
2. 代码占用小：最小配置下仅需几千字节ROM和几百字节RAM
3. 功能丰富：支持长文件名、多卷、多种编码页
4. 线程安全：支持RTOS环境下的多线程访问
5. 兼容性好：与Windows、Linux等系统完全兼容

配置模式对比

配置模式对比

配置模式	ROM占用	RAM占用	功能特点
最小配置	6-8KB	0.7-1KB	仅基本读写，无格式化和长文件名
标准配置	12-18KB	1.2-2KB	包含常用功能，支持有限长文件名
全功能配置	25-35KB	3-5KB	支持所有功能包括长文件名、格式化等

常见概念说明

扇区（Sector）的定义

扇区是存储设备（如 SD 卡、硬盘）的最小可寻址单元，通常大小为 512 字节或 4KB（取决于设备）。FatFS 通过 DISKIO 接口与物理设备交互时，所有读写操作均以扇区为单位。

#define FF_MIN_SS 512    // 最小扇区大小
#define FF_MAX_SS 4096   // 最大扇区大小
#define FF_USE_TRIM 0    // 是否启用块擦除功能

FATFS簇大小的定义

簇（Cluster）是FAT文件系统中分配存储空间的最小单位，由连续的扇区组成。一个文件占用的空间始终是簇大小的整数倍，即使文件实际大小不足一簇。

簇大小的影响因素

簇大小通常由卷（分区）大小和FAT类型（FAT12/FAT16/FAT32）决定：

FAT12：适用于小容量存储（如软盘），簇大小较小（如512B-4KB）。
FAT16：中容量存储，簇范围通常为2KB-32KB。
FAT32：大容量存储，簇范围多为4KB-32KB。
具体数值可通过格式化工具或磁盘属性查看，不同操作系统可能提供默认推荐值。

簇大小的优缺点

较小簇：减少空间浪费（尤其是小文件），但文件碎片化风险增加，管理开销更大。
较大簇：提升大文件读写效率，减少碎片，但小文件可能浪费更多空间（如1KB文件在32KB簇中占用32KB）。
计算公式
簇大小（Bytes）= 每簇扇区数 × 每扇区字节数（通常512B）。例如：

若每簇8扇区，则簇大小 = 8 × 512B = 4KB。

U盘/小容量设备：选择较小簇（如4KB）以优化空间利用率。
大容量硬盘：选择较大簇（如32KB）以提高性能。
通过diskgenius或Windows格式化工具可手动调整簇大小，需权衡存储效率与性能需求。

块（Block）的定义

块是 FatFS 文件系统的逻辑单元，由多个连续扇区组成。块大小在格式化时确定（如 1KB、4KB、32KB），必须是扇区大小的整数倍。块用于文件系统内部管理（如簇分配）。
块大小与簇的关系
1 簇（Cluster） = 1 块（Block）。
块越大，文件分配粒度越粗，可能浪费空间但性能更高。

格式化时指定块大小
通过 f_mkfs 函数的参数 opt 指定：

MKFS_PARM opt;
opt.fmt = FM_FAT32;      // 文件系统类型
opt.n_fat = 1;           // FAT 表数量
opt.au_size = 4096;      // 块大小（此处为 4KB）
f_mkfs("0:", &opt, work, sizeof(work));

四、FatFS 0.16移植指南

• 获取源码和准备工程
  从FatFS官网下载源码: elm-chan.org/fsw/ff/00index_e.html
• 将以下文件添加到工程
  source/ffsystem.c - FatFS系统锁 – 用户配置
  source/ff.c - FatFS核心模块
  source/ff.h - FatFS头文件
  source/diskio.c - 磁盘I/O模板 – 用户实现
  source/ffconf.h - 配置文件 – 用户裁剪
  source/ffunicode.c - FatFS字符编码
• 根据硬件平台创建硬件驱动文件

#include "ff.h"
#include "diskio.h"
#include "sd_card.h"  // 你的SD卡驱动头文件// 获取磁盘状态
DSTATUS disk_status(BYTE pdrv) {switch(pdrv) {case 0:  // 驱动器0return SD_GetStatus() ? 0 : STA_NOINIT;default:return STA_NOINIT;}
}// 初始化磁盘
DSTATUS disk_initialize(BYTE pdrv) {switch(pdrv) {case 0:if(SD_Init() == SD_OK) {return 0;} else {return STA_NOINIT;}default:return STA_NOINIT;}
}// 读取扇区
DRESULT disk_read(BYTE pdrv, BYTE *buff, LBA_t sector, UINT count) {switch(pdrv) {case 0:for(UINT i = 0; i < count; i++) {if(SD_ReadDisk(buff, sector + i, 1) != SD_OK) {return RES_ERROR;}buff += 512;  // 假设扇区大小为512字节}return RES_OK;default:return RES_PARERR;}
}// 写入扇区
DRESULT disk_write(BYTE pdrv, const BYTE *buff, LBA_t sector, UINT count) {switch(pdrv) {case 0:for(UINT i = 0; i < count; i++) {if(SD_WriteDisk(buff, sector + i, 1) != SD_OK) {return RES_ERROR;}buff += 512;}return RES_OK;default:return RES_PARERR;}
}// 磁盘控制
DRESULT disk_ioctl(BYTE pdrv, BYTE cmd, void *buff) {switch(pdrv) {case 0:switch(cmd) {case CTRL_SYNC:      // 确保写入完成SD_WaitWriteComplete();return RES_OK;case GET_SECTOR_SIZE: // 获取扇区大小*(WORD*)buff = 512;return RES_OK;case GET_BLOCK_SIZE:  // 获取擦除块大小*(DWORD*)buff = 1;return RES_OK;case GET_SECTOR_COUNT: // 获取总扇区数*(DWORD*)buff = SD_GetCapacity() / 512;return RES_OK;default:return RES_PARERR;}default:return RES_PARERR;}
}// 获取当前时间（用于文件时间戳）
DWORD get_fattime(void) {// 这里需要实现RTC获取时间，格式为：// bit31:25 - 年(0-127)从1980年算起// bit24:21 - 月(1-12)// bit20:16 - 日(1-31)// bit15:11 - 时(0-23)// bit10:5  - 分(0-59)// bit4:0   - 秒/2(0-29)// 示例：2023年10月15日 14:30:00return ((2023 - 1980) << 25) | (10 << 21) | (15 << 16) | (14 << 11) | (30 << 5) | (0 >> 1);
}

ffconf.h 详细配置说明

/*---------------------------------------------------------------------------/
/  FatFs Functional Configurations
/---------------------------------------------------------------------------*/#define FFCONF_DEF	80386	/* Revision ID *//*---------------------------------------------------------------------------/
/ Function Configurations
/---------------------------------------------------------------------------*/#define FF_FS_READONLY	0
/* This option switches read-only configuration. (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
/* This option defines minimization level to remove some basic API functions.
/
/   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
/* This option switches string functions, f_gets(), f_putc(), f_puts() and f_printf().
/
/  0: Disable string functions.
/  1: Enable without LF-CRLF conversion.
/  2: Enable with LF-CRLF conversion. */#define FF_USE_FIND		0  
/* This option switches filtered directory read functions, f_findfirst() and
/  f_findnext(). (0:Disable, 1:Enable 2:Enable with matching altname[] too) */#define FF_USE_MKFS		1
/* This option switches f_mkfs() function. (0:Disable or 1:Enable) */#define FF_USE_FASTSEEK	1
/* This option switches fast seek function. (0:Disable or 1:Enable) */#define FF_USE_EXPAND	0
/* This option switches f_expand function. (0:Disable or 1:Enable) */#define FF_USE_CHMOD	1
/* This option switches attribute manipulation functions, 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	1
/* This option switches volume label functions, f_getlabel() and f_setlabel().
/  (0:Disable or 1:Enable) */#define FF_USE_FORWARD	0
/* This option switches f_forward() function. (0:Disable or 1:Enable) *//*---------------------------------------------------------------------------/
/ Locale and Namespace Configurations
/---------------------------------------------------------------------------*/#define FF_CODE_PAGE	437
/* This option specifies the OEM code page to be used on the target system.
/  Incorrect code page setting can cause a file open failure.
/
/   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()
*/#define FF_USE_LFN		2
#define FF_MAX_LFN		255
/* The FF_USE_LFN switches the support for LFN (long file name).
/
/   0: Disable LFN. FF_MAX_LFN has no effect.
/   1: Enable LFN with static  working buffer on the BSS. Always NOT thread-safe.
/   2: Enable LFN with dynamic working buffer on the STACK.
/   3: Enable LFN with dynamic working buffer on the HEAP.
/
/  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 it 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() exemplified 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.
/
/   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
/* 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		2
/* This option configures support for relative path.
/
/   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
/---------------------------------------------------------------------------*/#define FF_VOLUMES		2
/* Number of volumes (logical drives) to be used. (1-10) */#define FF_STR_VOLUME_ID	0
#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	1
/* 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		512
/* 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_LBA64		0
/* This option switches support for 64-bit LBA. (0:Disable or 1:Enable)
/  To enable the 64-bit LBA, also exFAT needs to be enabled. (FF_FS_EXFAT == 1) */#define FF_MIN_GPT		0x100000000
/* Minimum number of sectors to switch GPT format to create partition in f_mkfs and
/  f_fdisk function. 0x100000000 max. This option has no effect when FF_LBA64 == 0. */#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. *//*---------------------------------------------------------------------------/
/ System Configurations
/---------------------------------------------------------------------------*/#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
/* 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	9
#define FF_NORTC_MDAY	1
#define FF_NORTC_YEAR	2020
/* 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 in read-only configuration (FF_FS_READONLY = 1). */#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.
*/#define FF_FS_LOCK		0
/* 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
/* 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
/      option/syscall.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 ---*/

FatFS主要接口使用详解

文件系统管理

挂载与卸载

FATFS fs;          // 文件系统对象
FRESULT res;       // 操作结果// 挂载文件系统
res = f_mount(&fs, "0:", 1);  // "0:"表示第一个驱动器，1:立即挂载
if (res != FR_OK) {printf("挂载失败: %d\n", res);if (res == FR_NO_FILESYSTEM) {printf("未找到文件系统，需要格式化...\n");// 格式化文件系统MKFS_PARM opt;opt.fmt = FM_FAT32;     // 文件系统类型opt.n_fat = 1;          // FAT表数量opt.align = 0;          // 卷对齐(0:自动)opt.n_root = 512;       // 根目录条目数opt.au_size = 0;        // 簇大小(0:自动)res = f_mkfs("0:", &opt, work, sizeof(work));if (res == FR_OK) {printf("格式化成功，重新挂载...\n");res = f_mount(&fs, "0:", 0);  // 重新挂载}}
}// 卸载文件系统（在程序退出或需要重新初始化时调用）
f_mount(NULL, "0:", 0);

获取文件系统信息

void show_fs_info(void) {FATFS *fs;DWORD fre_clust, fre_sect, tot_sect;// 获取驱动器状态res = f_getfree("0:", &fre_clust, &fs);if (res == FR_OK) {// 计算总空间和空闲空间tot_sect = (fs->n_fatent - 2) * fs->csize;fre_sect = fre_clust * fs->csize;printf("文件系统类型: FAT%d\n", (fs->fs_type == FS_FAT32) ? 32 : (fs->fs_type == FS_FAT16) ? 16 : 12);printf("总空间: %lu KB\n", tot_sect / 2);printf("可用空间: %lu KB\n", fre_sect / 2);printf("簇大小: %lu 扇区(%lu bytes)\n", fs->csize, fs->csize * 512);}
}

文件操作详解

常用宏定义

#define f_eof(fp) ((int)((fp)->fptr == (fp)->obj.objsize))
#define f_error(fp) ((fp)->err)
#define f_tell(fp) ((fp)->fptr)
#define f_size(fp) ((fp)->obj.objsize)
#define f_rewind(fp) f_lseek((fp), 0)
#define f_rewinddir(dp) f_readdir((dp), 0)
#define f_rmdir(path) f_unlink(path)
#define f_unmount(path) f_mount(0, path, 0)

基本文件操作

// 文件打开模式标志
#define FA_READ         0x01  // 读模式
#define FA_WRITE        0x02  // 写模式
#define FA_OPEN_EXISTING 0x00 // 打开已存在文件
#define FA_CREATE_NEW   0x04  // 创建新文件(文件存在则失败)
#define FA_CREATE_ALWAYS 0x08 // 总是创建新文件(覆盖已存在)
#define FA_OPEN_ALWAYS  0x10  // 打开或创建文件
#define FA_OPEN_APPEND  0x30  // 以追加模式打开// 文件属性标志
#define AM_RDO  0x01  // 只读
#define AM_HID  0x02  // 隐藏
#define AM_SYS  0x04  // 系统
#define AM_DIR  0x10  // 目录
#define AM_ARC  0x20  // 存档// 完整的文件操作示例
void file_operations(void) {FIL fil;UINT bw, br;FRESULT res;char buffer[128];// 1. 创建并写入文件res = f_open(&fil, "test.txt", FA_CREATE_ALWAYS | FA_WRITE);if (res == FR_OK) {// 写入数据f_write(&fil, "Hello FatFS!\n", 13, &bw);// 移动文件指针到指定位置f_lseek(&fil, 20);  // 移动到第20字节// 在指定位置写入数据f_write(&fil, "Data at position 20", 19, &bw);// 截断文件到当前指针位置f_truncate(&fil);// 确保数据写入物理设备f_sync(&fil);f_close(&fil);}// 2. 读取文件内容res = f_open(&fil, "test.txt", FA_READ);if (res == FR_OK) {// 获取文件大小FSIZE_t size = f_size(&fil);printf("文件大小: %lu bytes\n", size);// 读取文件内容while (f_gets(buffer, sizeof(buffer), &fil)) {printf("%s", buffer);}f_close(&fil);}// 3. 文件属性操作FILINFO fno;res = f_stat("test.txt", &fno);if (res == FR_OK) {printf("文件名: %s\n", fno.fname);printf("文件大小: %lu\n", fno.fsize);printf("修改时间: %u/%u/%u %u:%u:%u\n", (fno.fdate >> 9) + 1980, (fno.fdate >> 5) & 15, fno.fdate & 31,fno.ftime >> 11, (fno.ftime >> 5) & 63, (fno.ftime & 31) * 2);}// 4. 重命名文件f_rename("test.txt", "backup.txt");// 5. 删除文件f_unlink("backup.txt");
}

文件查找与遍历

void find_files(const char* path) {DIR dir;FILINFO fno;FRESULT res;res = f_opendir(&dir, path);if (res == FR_OK) {printf("目录 %s 内容:\n", path);while (1) {res = f_readdir(&dir, &fno);if (res != FR_OK || fno.fname[0] == 0) break;if (fno.fattrib & AM_DIR) {printf("  [DIR]  %s/\n", fno.fname);} else {printf("  [FILE] %s (%lu bytes)\n", fno.fname, fno.fsize);}}f_closedir(&dir);}
}// 递归遍历目录
void traverse_directory(const char* path, int depth) {DIR dir;FILINFO fno;char full_path[256];if (f_opendir(&dir, path) == FR_OK) {while (f_readdir(&dir, &fno) == FR_OK && fno.fname[0] != 0) {// 缩进显示层级for (int i = 0; i < depth; i++) printf("  ");if (fno.fattrib & AM_DIR) {printf("+ %s/\n", fno.fname);// 构建子目录路径并递归遍历snprintf(full_path, sizeof(full_path), "%s/%s", path, fno.fname);traverse_directory(full_path, depth + 1);} else {printf("- %s (%lu bytes)\n", fno.fname, fno.fsize);}}f_closedir(&dir);}
}

目录操作详解

void directory_operations(void) {FRESULT res;// 1. 创建目录res = f_mkdir("/data/logs");if (res == FR_OK) {printf("目录创建成功\n");} else if (res == FR_EXIST) {printf("目录已存在\n");}// 2. 切换当前目录f_chdir("/data/logs");// 3. 获取当前工作目录char cwd[256];res = f_getcwd(cwd, sizeof(cwd));if (res == FR_OK) {printf("当前目录: %s\n", cwd);}// 4. 删除空目录f_rmdir("/data/temp");
}

五、性能优化

应用层性能优化

簇大小优化

// 格式化时选择最优簇大小
void format_with_optimal_cluster(DWORD volume_size) {MKFS_PARM opt;opt.fmt = FM_FAT32;// 根据容量选择簇大小if (volume_size < 16 * 1024 * 1024) {      // <16MBopt.au_size = 512;   // 0.5KB簇} else if (volume_size < 128 * 1024 * 1024) { // <128MBopt.au_size = 4096;  // 4KB簇} else if (volume_size < 1024 * 1024 * 1024) { // <1GBopt.au_size = 8192;  // 8KB簇} else {opt.au_size = 32768; // 32KB簇}f_mkfs("0:", &opt, work, sizeof(work));
}

缓存策略优化

// 自定义缓存配置（需要在ffconf.h中启用相关选项）
#if FF_USE_EXPAND// 为频繁读写的文件增加缓存FIL fil;BYTE file_buffer[4096];  // 4KB文件缓存f_open(&fil, "frequent_file.dat", FA_READ | FA_WRITE);f_expand(&fil, sizeof(file_buffer), file_buffer);  // 设置自定义缓存
#endif

批量写入优化

// 批量写入数据，减少同步次数
void batch_write_optimized(const char* filename, const void* data, size_t size) {FIL fil;UINT bw;const size_t CHUNK_SIZE = 4096;  // 4KB chunksconst uint8_t* ptr = (const uint8_t*)data;f_open(&fil, filename, FA_CREATE_ALWAYS | FA_WRITE);// 分块写入while (size > 0) {size_t chunk = (size > CHUNK_SIZE) ? CHUNK_SIZE : size;f_write(&fil, ptr, chunk, &bw);ptr += chunk;size -= chunk;}// 最后一次性同步f_sync(&fil);f_close(&fil);
}

顺序写入/读取

FRESULT copy_file(const char* src, const char* dst)
{FIL src_file, dst_file;FRESULT fr;UINT br, bw;uint8_t buffer[2048]; // 2KB缓冲区// 打开源文件fr = f_open(&src_file, src, FA_READ);if (fr != FR_OK) return fr;// 创建目标文件fr = f_open(&dst_file, dst, FA_WRITE | FA_CREATE_ALWAYS);if (fr != FR_OK) {f_close(&src_file);return fr;}// 顺序复制数据while (1) {fr = f_read(&src_file, buffer, sizeof(buffer), &br);if (fr != FR_OK || br == 0) break;fr = f_write(&dst_file, buffer, br, &bw);if (fr != FR_OK || bw != br) break;}// 关闭文件f_close(&src_file);f_close(&dst_file);return fr;
}

避免频繁open/close

对频繁操作的文件，打开后保留句柄，不关闭文件

同一文件读写分句柄

// 写入句柄：使用追加模式，避免覆盖现有数据
f_open(&write_fil, "file.txt", FA_WRITE | FA_OPEN_APPEND);// 读取句柄：使用只读模式，避免意外修改
f_open(&read_fil, "file.txt", FA_READ);
//注意， 两个句柄状态不会自动同步，关闭后打开即可同步

定期碎片化清理

// 写入句柄：使用追加模式，避免覆盖现有数据
f_open(&write_fil, "file.txt", FA_WRITE | FA_OPEN_APPEND);// 读取句柄：使用只读模式，避免意外修改
f_open(&read_fil, "file.txt", FA_READ);
//注意， 两个句柄状态不会自动同步，关闭后打开即可同步

驱动层性能优化

通信时钟优化

根据卡的类型/MCU的外设 合理选择时钟频率

使能多扇区读写接口

DRESULT disk_read(BYTE pdrv, BYTE *buff, LBA_t sector, UINT count)
{
#define DISK_READ_MAX_RETRY 3uint32_t rt    = 0;uint32_t retry = 0;if (!count){return RES_PARERR;}switch (pdrv){case DEV_SD:if (count == 1){do{rt = sd_drv_single_block_read(sector, buff);} while (rt && retry++ < DISK_READ_MAX_RETRY);return ((rt == 0) ? RES_OK : RES_ERROR);}else{do{rt = sd_drv_mutil_block_read(sector, buff, count);} while (rt && retry++ < DISK_READ_MAX_RETRY);return ((rt == 0) ? RES_OK : RES_ERROR);}default:return RES_ERROR;}
}

使能DMA传输

使能DMA传输，合理配置中断优先级

SD卡命令判断策略

避免在SD卡命令返回判断中使用延时等待

总结

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