The FATFS structure (filesystem 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 of the structure is done by volume mount process whenever necessary. Application program must not modify any member in this structure, or the FAT volume will be collapsed.
typedef struct { BYTE fs_type; /* FAT type (0, FS_FAT12, FS_FAT16, FS_FAT32 or FS_EXFAT) */ BYTE pdrv; /* Hosting physical drive of this volume */ 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; /* Volume mount ID */ WORD n_rootdir; /* Number of root directory entries (FAT12/16) */ WORD csize; /* Sectors per cluster */ #if FF_MAX_SS != FF_MIN_SS WORD ssize; /* Sector size (512,1024,2048 or 4096) */ #endif #if FF_FS_EXFAT BYTE* dirbuf; /* Directory entry block scratchpad buffer */ #endif #if FF_FS_REENTRANT FF_SYNC_t sobj; /* Identifier of sync object */ #endif #if !FF_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 FF_FS_RPATH DWORD cdir; /* Cluster number of current directory (0:root) */ #if FF_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 */ LBA_t volbase; /* Volume base LBA */ LBA_t fatbase; /* FAT base LBA */ LBA_t dirbase; /* Root directory base (LBA|Cluster) */ LBA_t database; /* Data base LBA */ LBA_t winsect; /* Sector LBA appearing in the win[] */ BYTE win[FF_MAX_SS]; /* Disk access window for directory, FAT (and file data at tiny cfg) */ } FATFS;