fatfs/documents/doc/sync.html

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   9 <title>FatFs - f_sync</title>
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  13
  14 <div class="para func">
  15 <h2>f_sync</h2>
  16 <p>The f_sync function flushes the cached information of a writing file.</p>
  17 <pre>
  18 FRESULT f_sync (
  19   FIL* <span class="arg">fp</span>     <span class="c">/* [IN] File object */</span>
  20 );
  21 </pre>
  22 </div>
  23
  24 <div class="para arg">
  25 <h4>Parameter</h4>
  26 <dl class="par">
  27 <dt>fp</dt>
  28 <dd>Pointer to the open file object to be flushed.</dd>
  29 </dl>
  30 </div>
  31
  32
  33 <div class="para ret">
  34 <h4>Return Values</h4>
  35 <p>
  36 <a href="rc.html#ok">FR_OK</a>,
  37 <a href="rc.html#de">FR_DISK_ERR</a>,
  38 <a href="rc.html#ie">FR_INT_ERR</a>,
  39 <a href="rc.html#io">FR_INVALID_OBJECT</a>,
  40 <a href="rc.html#tm">FR_TIMEOUT</a>
  41 </p>
  42 </div>
  43
  44
  45 <div class="para desc">
  46 <h4>Description</h4>
  47 <p>The <tt>f_sync</tt> function performs the same process as <tt>f_close</tt> 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 <tt>f_sync</tt> function in certain interval can minimize the risk of data loss due to a sudden blackout, wrong media removal or unrecoverable disk error. For more information, refer to <a href="appnote.html#critical">application note</a>.</p>
  48 <pre>
  49 Case 1. Normal write sequence
  50
  51                                 Time --&gt;                                     ↓Normal shutdown
  52 OwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwC &lt;Power off&gt;
  53
  54
  55 Case 2. Without using f_sync()
  56
  57                                 Time --&gt;                             ↓System crush
  58 O<span class="e">wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww</span>
  59  |&lt;--------------- All data written will be lost ------------------&gt;|
  60
  61
  62 Case 3. Using f_sync()
  63                                 Time --&gt;                             ↓System crush
  64 OwwwwwwwwSwwwwwwwwSwwwwwwwwSwwwwwwwwSwwwwwwwwSwwwwwwwwSwwwwwwwwS<span class="e">wwwww</span>
  65                             Data after last f_sync will be lost |&lt;-&gt;|
  66 O - f_open()
  67 C - f_close()
  68 w - f_write()
  69 S - f_sync()
  70 </pre>
  71 <p>However there is no sense in <tt>f_sync</tt> function immediataly before <tt>f_close</tt> function because it performs <tt>f_sync</tt> function in it. In other words, the differnce between those functions is that the file object is invalidated or not.</p>
  72 </div>
  73
  74
  75 <div class="para comp">
  76 <h4>QuickInfo</h4>
  77 <p>Available when <tt><a href="config.html#fs_readonly">FF_FS_READONLY</a> == 0</tt>.</p>
  78 </div>
  79
  80
  81 <div class="para ref">
  82 <h4>See Also</h4>
  83 <p><tt><a href="close.html">f_close</a></tt>, <a href="appnote.html#critical">Critical section</a></p>
  84 </div>
  85
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