FRESULT f_mkfs (
  const TCHAR* path,  /* [IN] Logical drive number */
  BYTE  opt,          /* [IN] Format options */
  DWORD au,           /* [IN] Size of the allocation unit */
  void* work,         /* [-]  Working buffer */
  UINT len            /* [IN] Size of working buffer */
);

Description

The FAT sub-type, FAT12/FAT16/FAT32, of FAT volume except exFAT is determined by only number of clusters on the volume and nothing else, according to the FAT specification issued by Microsoft. Thus the FAT sub-type of created volume depends on the volume size and the cluster size. In case of the combination of FAT type and cluter size specified by argument cannot be valid on the volume, the function will fail with FR_MKFS_ABORTED. The minimum drive size is 128 sectors with FM_SFD option.

The allocation unit, also called cluster, is a unit of disk space allocation for files. When the size of allocation unit is 32768 bytes, a file with 100 bytes in size occupies 32768 bytes of disk space. The space efficiency of disk usage gets worse as increasing size of allocation unit, but, on the other hand, the read/write performance increases as the size of allocation unit. Therefore the size of allocation unit is a trade-off between space efficiency and performance. For the large storages in GB order, 32768 bytes or larger (this is automatically selected by default) is recommended for most case unless extremely many small files are created on a volume.

There are three disk partitioning formats, FDISK, SFD and GPT. The FDISK format is usually used for harddisk, memory card and U disk. It can divide a physical drive into one or more partitions with a partition table on the MBR (maser boot record, the first sector of the physical drive). The SFD (super-floppy disk) is non-partitioned disk format. The FAT volume starts at the first sector of the physical drive without any disk partitioning. It is usually used for floppy disk, optical disk and most super-floppy media. Some systems support only either one of the two disk formats and the other is not supported. The GPT (GUID Partition Table) is a newly defined format for large storage devices. FatFs does not support the storages with GPT.

When the logical drive to be formatted is bound to a physical drive and FM_SFD is not specified, a primary partition occupies whole drive space is created in FDISK format, and then the FAT volume is created in the partition. When FM_SFD is specified, the FAT volume occupies from the first sector of the physical drive is created in SFD format.

When the logical drive to be formatted is bound to a specific partition (1-4) by support of multiple partition (FF_MULTI_PARTITION == 1), the FAT volume is created on the partition and FM_SFD flag is ignored. The physical drive needs to be partitioned with f_fdisk function or any other partitioning tools prior to create the FAT volume with this function.

/* Format default drive and create a file */
int main (void)
{
    FATFS fs;           /* Filesystem object */
    FIL fil;            /* File object */
    FRESULT res;        /* API result code */
    UINT bw;            /* Bytes written */
    BYTE work[FF_MAX_SS]; /* Work area (larger is better for processing time) */


    /* Create FAT volume */
    res = f_mkfs("", FM_ANY, 0, work, sizeof work);
    if (res) ...

    /* Register work area */
    f_mount(&fs, "", 0);

    /* Create a file as new */
    res = f_open(&fil, "hello.txt", FA_CREATE_NEW | FA_WRITE);
    if (res) ...

    /* Write a message */
    f_write(&fil, "Hello, World!\r\n", 15, &bw);
    if (bw != 15) ...

    /* Close the file */
    f_close(&fil);

    /* Unregister work area */
    f_mount(0, "", 0);

    ...