File IO Lib API
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void fl_init(void)

  Called to initialize FAT IO library.
  This should be called prior to any other functions.

void fl_attach_locks(void (*lock)(void), void (*unlock)(void))

  [Optional] File system thread safety locking functions.
  For thread safe operation, you should provide lock() and unlock() functions.
  Note that locking primitive used must support recursive locking, i.e lock() called within an already ‘locked’ region.

int fl_attach_media(fn_diskio_read rd, fn_diskio_write wr)

  This function is used to attach system specific disk/media access functions.  
  This should be done subsequent to calling fl_init() and fl_attach_locks() (if locking required).

void fl_shutdown(void)

  Shutdown the FAT IO library. This purges any un-saved data back to disk.