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-<link rel="up" title="FatFs" href="../00index_e.html">\r
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-<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 first item of the <em>byte array</em> to store read data.</dd>\r
-<dt>sector</dt>\r
-<dd>Start sector number in 32-bit LBA.</dd>\r
-<dt>count</dt>\r
-<dd>Number of sectors to read.</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 data read/write operation to the storage devices is done in unit of <em>sector</em>. FatFs supports the sector size in range of from 512 to 4096 bytes. When FatFs is configured to fixed sector size (<tt>_MIN_SS == MAX_SS</tt>, this will be the most case), the read/write function must work at that sector size. When FatFs is configured to variable sector size (<tt>_MIN_SS != MAX_SS</tt>), sector size is inquired with <tt>disk_ioctl</tt> function following <tt>disk_initialize</tt> function.</p>\r
-<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>\r
-<ul>\r
-<li>Convert word transfer to byte transfer in this function if needed. - Recommended.</li>\r
-<li>On the <tt>f_read</tt> calls, avoid long read request that includes a whole of sector. - Any direct transfer never occures.</li>\r
-<li>On the <tt>f_read</tt> calls, make sure that <tt>(((UINT)data & 3) == (f_tell(fp) & 3))</tt> is true. - Word alignment of <tt>buff</tt> 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
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projects / z180-stamp.git / blobdiff