savelij13
93faa45738
- Added arbitrary strings as drive number in the path name. (_STR_VOLUME_ID) - Added a configuration option of minimum sector size. (_MIN_SS) - 2nd argument of f_rename() can have a drive number and it will be ignored. - Fixed f_mount() with forced mount fails when drive number is >= 1. - Fixed f_close() invalidates the file object without volume lock. - Fixed f_closedir() returns but the volume lock is left acquired. - Fixed creation of an entry with LFN fails on too many SFN collisions.
72 lines
2.9 KiB
HTML
72 lines
2.9 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
|
|
<html lang="en">
|
|
<head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
|
|
<meta http-equiv="Content-Style-Type" content="text/css">
|
|
<link rel="up" title="FatFs" href="../00index_e.html">
|
|
<link rel="alternate" hreflang="ja" title="Japanese" href="../ja/dread.html">
|
|
<link rel="stylesheet" href="../css_e.css" type="text/css" media="screen" title="ELM Default">
|
|
<title>FatFs - disk_read</title>
|
|
</head>
|
|
|
|
<body>
|
|
|
|
<div class="para func">
|
|
<h2>disk_read</h2>
|
|
<p>The disk_read function reads sector(s) from the storage device.</p>
|
|
<pre>
|
|
DRESULT disk_read (
|
|
BYTE <span class="arg">pdrv</span>, <span class="c">/* [IN] Physical drive number */</span>
|
|
BYTE* <span class="arg">buff</span>, <span class="c">/* [OUT] Pointer to the read data buffer */</span>
|
|
DWORD <span class="arg">sector</span>, <span class="c">/* [IN] Start sector number */</span>
|
|
UINT <span class="arg">count</span> <span class="c">/* [IN] Number of sectros to read */</span>
|
|
);
|
|
</pre>
|
|
</div>
|
|
|
|
<div class="para arg">
|
|
<h4>Parameters</h4>
|
|
<dl class="par">
|
|
<dt>pdrv</dt>
|
|
<dd>Physical drive number to identify the target device.</dd>
|
|
<dt>buff</dt>
|
|
<dd>Pointer to the <em>byte array</em> to store the read data.</dd>
|
|
<dt>sector</dt>
|
|
<dd>Start sector number in logical block address (LBA).</dd>
|
|
<dt>count</dt>
|
|
<dd>Number of sectors to read. FatFs specifis it in range of from 1 to 128.</dd>
|
|
</dl>
|
|
</div>
|
|
|
|
|
|
<div class="para ret">
|
|
<h4>Return Value</h4>
|
|
<dl class="ret">
|
|
<dt>RES_OK (0)</dt>
|
|
<dd>The function succeeded.</dd>
|
|
<dt>RES_ERROR</dt>
|
|
<dd>Any hard error occured during the read operation and could not recover it.</dd>
|
|
<dt>RES_PARERR</dt>
|
|
<dd>Invalid parameter.</dd>
|
|
<dt>RES_NOTRDY</dt>
|
|
<dd>The device has not been initialized.</dd>
|
|
</dl>
|
|
</div>
|
|
|
|
|
|
<div class="para desc">
|
|
<h4>Description</h4>
|
|
<p>The memory address specified by <tt class="arg">buff</tt> is not that always aligned to word boundary because the type of argument is defined as <tt>BYTE*</tt>. The misaligned read/write request can occure at <a href="appnote.html#fs1">direct transfer</a>. If the bus architecture, especially DMA controller, does not allow misaligned memory access, it should be solved in this function. There are some workarounds described below to avoid this issue.</p>
|
|
<ul>
|
|
<li>Convert word transfer to byte transfer in this function. - Recommended.</li>
|
|
<li>For <tt>f_read()</tt>, avoid long read request that includes a whole of sector. - Direct transfer will never occure.</li>
|
|
<li>For <tt>f_read(fp, buff, btr, &br)</tt>, make sure that <tt>(((UINT)buff & 3) == (f_tell(fp) & 3))</tt> is true. - Word aligned direct transfer is guaranteed.</li>
|
|
</ul>
|
|
<p>Generally, a multiple sector transfer request must not be split into single sector transactions to the storage device, or you will not get good read throughput.</p>
|
|
</div>
|
|
|
|
|
|
<p class="foot"><a href="../00index_e.html">Return</a></p>
|
|
</body>
|
|
</html>
|