--- /dev/null
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+<head>\r
+<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">\r
+<meta http-equiv="Content-Style-Type" content="text/css">\r
+<link rel="up" title="FatFs" href="../00index_e.html">\r
+<link rel="alternate" hreflang="ja" title="Japanese" href="../ja/dread.html">\r
+<link rel="stylesheet" href="../css_e.css" type="text/css" media="screen" title="ELM Default">\r
+<title>FatFs - disk_read</title>\r
+</head>\r
+\r
+<body>\r
+\r
+<div class="para func">\r
+<h2>disk_read</h2>\r
+<p>The disk_read function reads sector(s) from the storage device.</p>\r
+<pre>\r
+DRESULT disk_read (\r
+ BYTE <span class="arg">pdrv</span>, <span class="c">/* [IN] Physical drive number */</span>\r
+ BYTE* <span class="arg">buff</span>, <span class="c">/* [OUT] Pointer to the read data buffer */</span>\r
+ DWORD <span class="arg">sector</span>, <span class="c">/* [IN] Start sector number */</span>\r
+ UINT <span class="arg">count</span> <span class="c">/* [IN] Number of sectros to read */</span>\r
+);\r
+</pre>\r
+</div>\r
+\r
+<div class="para arg">\r
+<h4>Parameters</h4>\r
+<dl class="par">\r
+<dt>pdrv</dt>\r
+<dd>Physical drive number to identify the target device.</dd>\r
+<dt>buff</dt>\r
+<dd>Pointer to the <em>byte array</em> to store the read data.</dd>\r
+<dt>sector</dt>\r
+<dd>Start sector number in logical block address (LBA).</dd>\r
+<dt>count</dt>\r
+<dd>Number of sectors to read. FatFs specifis it in range of from 1 to 128.</dd>\r
+</dl>\r
+</div>\r
+\r
+\r
+<div class="para ret">\r
+<h4>Return Value</h4>\r
+<dl class="ret">\r
+<dt>RES_OK (0)</dt>\r
+<dd>The function succeeded.</dd>\r
+<dt>RES_ERROR</dt>\r
+<dd>Any hard error occured during the read operation and could not recover it.</dd>\r
+<dt>RES_PARERR</dt>\r
+<dd>Invalid parameter.</dd>\r
+<dt>RES_NOTRDY</dt>\r
+<dd>The device has not been initialized.</dd>\r
+</dl>\r
+</div>\r
+\r
+\r
+<div class="para desc">\r
+<h4>Description</h4>\r
+<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>\r
+<ul>\r
+<li>Convert word transfer to byte transfer in this function. - Recommended.</li>\r
+<li>For <tt>f_read()</tt>, avoid long read request that includes a whole of sector. - Direct transfer will never occure.</li>\r
+<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>\r
+</ul>\r
+<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>\r
+</div>\r
+\r
+\r
+<p class="foot"><a href="../00index_e.html">Return</a></p>\r
+</body>\r
+</html>\r
projects / z180-stamp.git / blobdiff