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FatFs R0.13a, released October 14, 2017

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Christopher Williams
2017-11-11 23:43:22 -07:00
parent 5c7915feab
commit 7ee1f4cc87
61 changed files with 1240 additions and 779 deletions
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documents/doc/dread.html
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@@ -1,7 +1,7 @@
<!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-Type" content="text/html; charset=utf-8">
<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">
@@ -56,12 +56,12 @@ DRESULT disk_read (
<div class="para desc">
<h4>Description</h4>
<p>Read/write operation to the generic storage devices, such as memory card, hadddisk and optical disk, is done in unit of block of data bytes called <em>sector</em>. FatFs supports the sector size in range of from 512 to 4096 bytes. When FatFs is configured for fixed sector size (<tt>FF_MIN_SS == MAX_SS</tt>, this is the most case), the read/write function must work at that sector size. When FatFs is configured for variable sector size (<tt>FF_MIN_SS != MAX_SS</tt>), the sector size of medium is inquired with <tt>disk_ioctl</tt> function immediately following <tt>disk_initialize</tt> function.</p>
<p>Read/write operation to the generic storage devices, such as memory card, hadddisk and optical disk, is done in unit of block of data bytes called <em>sector</em>. FatFs supports the sector size in range of from 512 to 4096 bytes. When FatFs is configured for fixed sector size (<tt>FF_MIN_SS == FF_MAX_SS</tt>, this is the most case), the read/write function must work at that sector size. When FatFs is configured for variable sector size (<tt>FF_MIN_SS != FF_MAX_SS</tt>), the sector size of medium is inquired with <tt>disk_ioctl</tt> function immediately following <tt>disk_initialize</tt> function.</p>
<p>The memory address specified by <tt class="arg">buff</tt> is not that always aligned to word boundary because the argument is defined as <tt>BYTE*</tt>. The unaligned read/write request can occure at <a href="appnote.html#fs1">direct transfer</a>. If the bus architecture, especially DMA controller, does not allow unaligned 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 if needed. - Recommended.</li>
<li>On the <tt>f_read()</tt> calls, avoid long read request that includes a whole of sector. - Any direct transfer never occures.</li>
<li>On the <tt>f_read(fp, data, btw, bw)</tt> calls, make sure that <tt>(((UINT)data &amp; 3) == (f_tell(fp) &amp; 3))</tt> is true. - Word alignment of <tt class="arg">buff</tt> is guaranteed.</li>
<li>On the <tt>f_read(fp, dat, btw, bw)</tt> calls, make sure that <tt>(((UINT)dat &amp; 3) == (f_tell(fp) &amp; 3))</tt> is true. - Word alignment of <tt class="arg">buff</tt> is guaranteed no matter dat is not word aligned.</li>
</ul>
<p>Generally, a multiple sector read request must not be split into single sector transactions to the storage device, or read throughput gets worse.</p>
</div>