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;      /* FAT sub-type (0:Not mounted, FS_FAT12/FS_FAT16/FS_FAT32) */
    BYTE    drv;          /* Physical drive number */
    BYTE    csize;        /* Sectors per cluster (1,2,4,...,128) */
    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) */
#if _MAX_SS != _MIN_SS
    WORD    ssize;        /* Sector size (512,1024,2048 or 4096) */
#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) */
#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;