## FATFS

The `FATFS` structure (file system object) holds dynamic work area of individual logical drives. It is given by application program and registerd/unregisterd to the FatFs module with `f_mount` function. Initialization is done on first API call after `f_mount` function or media change. Application program must not modify any member in this structure, or any data on the FAT volume can be collapsed.

    typedef struct {
        BYTE    fs_type;      /* File system type (0, FS_FAT12, FS_FAT16, FS_FAT32 or FS_EXFAT) */
        BYTE    drv;          /* Physical drive number */
        BYTE    n_fats;       /* Number of FAT copies (1,2) */
        BYTE    wflag;        /* win[] flag (b0:win[] is dirty) */
        BYTE    fsi_flag;     /* FSINFO flags (b7:Disabled, b0:Dirty) */
        WORD    id;           /* File system mount ID */
        WORD    n_rootdir;    /* Number of root directory entries (FAT12/16) */
        WORD    csize;        /* Sectors per cluster */
    #if _MAX_SS != _MIN_SS
        WORD    ssize;        /* Sector size (512,1024,2048 or 4096) */
    #endif
    #if _FS_EXFAT
        BYTE*   dirbuf;       /* Directory entry block scratchpad buffer */
    #endif
    #if _FS_REENTRANT
        _SYNC_t sobj;         /* Identifier of sync object */
    #endif
    #if !_FS_READONLY
        DWORD   last_clust;   /* FSINFO: Last allocated cluster (0xFFFFFFFF if invalid) */
        DWORD   free_clust;   /* FSINFO: Number of free clusters (0xFFFFFFFF if invalid) */
    #endif
    #if _FS_RPATH
        DWORD   cdir;         /* Cluster number of current directory (0:root) */
    #if _FS_EXFAT
        DWORD   cdc_scl;      /* Containing directory start cluster (invalid when cdir is 0) */
        DWORD   cdc_size;     /* b31-b8:Size of containing directory, b7-b0: Chain status */
        DWORD   cdc_ofs;      /* Offset in the containing directory (invalid when cdir is 0) */
    #endif
    #endif
        DWORD   n_fatent;     /* Number of FAT entries (Number of clusters + 2) */
        DWORD   fsize;        /* Sectors per FAT */
        DWORD   volbase;      /* Volume base LBA */
        DWORD   fatbase;      /* FAT base LBA */
        DWORD   dirbase;      /* Root directory base (LBA|Cluster) */
        DWORD   database;     /* Data base LBA */
        DWORD   winsect;      /* Sector LBA appearing in the win[] */
        BYTE    win[_MAX_SS]; /* Disk access window for directory, FAT (and file data at tiny cfg) */
    } FATFS;

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