Using FatFs, file size limited to Allocation Unit Size of SD card

Started by kunalb 5 years ago2 replieslatest reply 5 years ago1915 views

I am trying to connect microSD card (8GB SanDisk SDHC) to MSP430F67791 controller via SPI interface (USCI_B1).

I am using Fatfs library (latest R0.12b) for this. (

I am able to write to a .csv file successfully. The problem is that my file size is getting restricted to the Allocation Unit Size that is set during formatting of SD card as FAT32. The max Allocation Unit Size that can be set to an 8GB SDHC card is 64KB. I am not able to write into the file after it grows to 64KB. Is there something to be done once the file size reaches Allocation Unit Size of the SD card ?

If I set Allocation Unit Size as 4KB, then the problem occurs at 4KB.

My file is a .csv file that I create on SD card before connecting it to MSP430 controller.

I'm calling f_write() 100 times before f_sync() and f_close(). So my code is as follows in a continuous loop :

do        {        fMountStatus = f_mount (&myFs, "0:", 1);        }        
while(f_mount_timeout-- && fMountStatus);
do        {        fOpenStatus = f_open(&fileObject, fileName, FA_OPEN_APPEND | FA_WRITE | FA_READ); }       
while(f_open_timeout-- && fOpenStatus);
while(f_write_count < 100)  // f_write_count initialized to 0      
f_write_timeout = 10;        
do        {        fWriteStatus = f_write(&fileObject, content, (stringSize-1), &bytesWritten);  }        
while(f_write_timeout-- && fWriteStatus);
do        {        fsyncStatus = f_sync(&fileObject);        }        
while(f_sync_timeout-- && fSyncStatus);
do        {        fcloseStatus = f_close(&fileObject);        } 
while(f_close_timeout-- && fcloseStatus);

I was hoping that after the file size reaches Allocation Unit Size of the SD card, f_close() & then f_mount() would take care of increasing the file size because I observed that after a reset to the system, it could write beyond Allocation Unit Size (be it 4KB or 64KB). But I do not wish to reset my system for that. Is there any straight forward way to handle this situation ?

[ - ]
Reply by mirceacNovember 3, 2016

Hello, I was looking at your code and I hope that is just an example and not even close to production, because, no offense, but is really bad.

First thing first: You have no delay function and when the file size gets over the cluster size, then the library tries to update the FAT tables, erase the next sector on the SD card and so on, this tales time and calling 10-20 time the same function in a tight loop will just get you nothing.

So in your loops call the delay function with at least 10ms delay. And have a look on the return code, it could tell you something ;).

Also do not forget to format the card before using it, most of the time people forget that the SD cards nowadays are not coming correctly formated for the the FatFS library

[ - ]
Reply by kunalbNovember 4, 2016

Thanks. The code I posted is a test code. My aim is to write approx 100 bytes to SD card every 3 secs. So I'm calling f_mount(), f_open() once to initialize the SD card and then calling f_write() every 3 secs and f_sync() every 30 secs.

The do-while loop, for FatFs function calls in the code above, calls the function repeatedly only if it fails. It does not unconditionally call the functions 10 times. I included a 10 ms delay inside the do-while but still see the same problem.

I have already formatted the SD card on my computer to FAT32 and have set the allocation unit size as 4KB for now.

My ffconf.h is as below. The options that I changed are _USE_LFN, _FS_EXFAT, _FS_NORTC.

Do you see a potential problem here ?

/  FatFs - FAT file system module configuration file

#define _FFCONF 68020    /* Revision ID */

/ Function Configurations

#define _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 _FS_MINIMIZE    0
/* This option defines minimization level to remove some basic API functions.
/   0: All basic functions are 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    _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 _USE_FIND        1
/* This option switches filtered directory read functions, f_findfirst() and
/  f_findnext(). (0:Disable, 1:Enable 2:Enable with matching altname[] too) */

#define    _USE_MKFS        1
/* This option switches f_mkfs() function. (0:Disable or 1:Enable) */

#define    _USE_FASTSEEK    0
/* This option switches fast seek function. (0:Disable or 1:Enable) */

#define    _USE_EXPAND        1
/* This option switches f_expand function. (0:Disable or 1:Enable) */

#define _USE_CHMOD        1
/* This option switches attribute manipulation functions, f_chmod() and f_utime().
/  (0:Disable or 1:Enable) Also _FS_READONLY needs to be 0 to enable this option. */

#define _USE_LABEL        1
/* This option switches volume label functions, f_getlabel() and f_setlabel().
/  (0:Disable or 1:Enable) */

#define    _USE_FORWARD    0
/* This option switches f_forward() function. (0:Disable or 1:Enable) */

/ Locale and Namespace Configurations

#define _CODE_PAGE    932
/* This option specifies the OEM code page to be used on the target system.
/  Incorrect setting of the code page can cause a file open failure.
/   1   - ASCII (No extended character. Non-LFN cfg. only)
/   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)

#define    _USE_LFN    0       ////// CHANGED
#define    _MAX_LFN    255
/* The _USE_LFN switches the support of long file name (LFN).
/   0: Disable support of LFN. _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, Unicode handling functions (option/unicode.c) must be added
/  to the project. The working buffer occupies (_MAX_LFN + 1) * 2 bytes and
/  additional 608 bytes at exFAT enabled. _MAX_LFN can be in range from 12 to 255.
/  It should be set 255 to support full featured LFN operations.
/  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(), must be added to the project. */

#define    _LFN_UNICODE    0
/* This option switches character encoding on the API. (0:ANSI/OEM or 1:UTF-16)
/  To use Unicode string for the path name, enable LFN and set _LFN_UNICODE = 1.
/  This option also affects behavior of string I/O functions. */

#define _STRF_ENCODE    3
/* When _LFN_UNICODE == 1, this option selects the character encoding ON THE FILE to
/  be read/written via string I/O functions, f_gets(), f_putc(), f_puts and f_printf().
/  0: ANSI/OEM
/  1: UTF-16LE
/  2: UTF-16BE
/  3: UTF-8
/  This option has no effect when _LFN_UNICODE == 0. */

#define _FS_RPATH    2
/* This option configures support of 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 _VOLUMES    2
/* Number of volumes (logical drives) to be used. */

#define _STR_VOLUME_ID    0
#define _VOLUME_STRS    "RAM","NAND","CF","SD","SD2","USB","USB2","USB3"
/* _STR_VOLUME_ID switches string support of volume ID.
/  When _STR_VOLUME_ID is set to 1, also pre-defined strings can be used as drive
/  number in the path name. _VOLUME_STRS defines the drive ID strings for each
/  logical drives. Number of items must be equal to _VOLUMES. Valid characters for
/  the drive ID strings are: A-Z and 0-9. */

#define    _MULTI_PARTITION    0
/* This option switches support of multi-partition on a 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 multi-partition 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    _MIN_SS        512
#define    _MAX_SS        512
/* These options configure the range of sector size to be supported. (512, 1024,
/  2048 or 4096) Always set both 512 for most systems, all type of memory cards and
/  harddisk. But a larger value may be required for on-board flash memory and some
/  type of optical media. When _MAX_SS is larger than _MIN_SS, FatFs is configured
/  to variable sector size and GET_SECTOR_SIZE command must be implemented to the
/  disk_ioctl() function. */

#define    _USE_TRIM    0
/* This option switches support of ATA-TRIM. (0:Disable or 1:Enable)
/  To enable Trim function, also CTRL_TRIM command should be implemented to the
/  disk_ioctl() function. */

#define _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

#define    _FS_TINY    1
/* This option switches tiny buffer configuration. (0:Normal or 1:Tiny)
/  At the tiny configuration, size of the file object (FIL) is reduced _MAX_SS bytes.
/  Instead of private sector buffer eliminated from the file object, common sector
/  buffer in the file system object (FATFS) is used for the file data transfer. */

#define _FS_EXFAT    0       ///// CHANGED
/* This option switches support of exFAT file system in addition to the traditional
/  FAT file system. (0:Disable or 1:Enable) To enable exFAT, also LFN must be enabled.
/  Note that enabling exFAT discards C89 compatibility. */

#define _FS_NORTC    1       /// CHANGED, dont need RTC
#define _NORTC_MON    5
#define _NORTC_MDAY    1
#define _NORTC_YEAR    2016
/* The option _FS_NORTC switches timestamp functiton. If the system does not have
/  any RTC function or valid timestamp is not needed, set _FS_NORTC = 1 to disable
/  the timestamp function. All objects modified by FatFs will have a fixed timestamp
/  defined by _NORTC_MON, _NORTC_MDAY and _NORTC_YEAR in local time.
/  To enable timestamp function (_FS_NORTC = 0), get_fattime() function need to be
/  added to the project to get current time form real-time clock. _NORTC_MON,
/  _NORTC_MDAY and _NORTC_YEAR have no effect. 
/  These options have no effect at read-only configuration (_FS_READONLY = 1). */

#define    _FS_LOCK    0
/* The option _FS_LOCK switches file lock function to control duplicated file open
/  and illegal operation to open objects. This option must be 0 when _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. */

#define _FS_REENTRANT    0
#define _FS_TIMEOUT        1000
#define    _SYNC_t            HANDLE
/* The option _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. _FS_TIMEOUT and _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 _FS_TIMEOUT defines timeout period in unit of time tick.
/  The _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.c. */

/*--- End of configuration options ---*/