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diff --git a/thirdparty/nRF5_SDK_15.0.0_a53641a/external/fatfs/doc/en/dread.html b/thirdparty/nRF5_SDK_15.0.0_a53641a/external/fatfs/doc/en/dread.html new file mode 100644 index 0000000..1265aa3 --- /dev/null +++ b/thirdparty/nRF5_SDK_15.0.0_a53641a/external/fatfs/doc/en/dread.html @@ -0,0 +1,72 @@ +<!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 first item of the <em>byte array</em> to store read data.</dd> +<dt>sector</dt> +<dd>Start sector number in 32-bit LBA.</dd> +<dt>count</dt> +<dd>Number of sectors to read.</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 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> +<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</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> +</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> |