FRESULT f_sync (
  FIL* fp     /* [IN] File object */
);

Description

The f_sync function performs the same process as f_close function but the file is left opened and can continue read/write/seek operations to the file. This is suitable for the applications that open files for a long time in write mode, such as data logger. Performing f_sync function in certain interval can minimize the risk of data loss due to a sudden blackout or an unintentional media removal. For more information, refer to application note.

Case 1. Normal write sequence

                                Time -->                                     ↓Power off after close
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Case 2. Without using f_sync()

                                Time -->                             ↓System crush
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 |<--------------- All data written will be lost ------------------>|


Case 3. Using f_sync()
                                Time -->                             ↓System crush
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                            Data after last f_sync will be lost |<->| 
O - f_open()
C - f_close()
w - f_write()
S - f_sync()

However there is no sense in f_sync function immediataly before f_close function because it performs f_sync function in it. In other words, the differnce between those functions is that the file object is invalidated or not.