projects / z180-stamp.git / blame
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1 | <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">\r |
| 2 | <html lang="en">\r | |
| 3 | <head>\r | |
| 289f6a14 | 4 | <meta http-equiv="Content-Type" content="text/html; charset=utf-8">\r |
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5 | <meta http-equiv="Content-Style-Type" content="text/css">\r |
| 6 | <link rel="up" title="FatFs" href="../00index_e.html">\r | |
| 7 | <link rel="alternate" hreflang="ja" title="Japanese" href="../ja/dread.html">\r | |
| 8 | <link rel="stylesheet" href="../css_e.css" type="text/css" media="screen" title="ELM Default">\r | |
| 9 | <title>FatFs - disk_read</title>\r | |
| 10 | </head>\r | |
| 11 | \r | |
| 12 | <body>\r | |
| 13 | \r | |
| 14 | <div class="para func">\r | |
| 15 | <h2>disk_read</h2>\r | |
| 289f6a14 | 16 | <p>The disk_read function is called to read data from the sector(s) of storage device.</p>\r |
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17 | <pre>\r |
| 18 | DRESULT disk_read (\r | |
| 19 | BYTE <span class="arg">pdrv</span>, <span class="c">/* [IN] Physical drive number */</span>\r | |
| 20 | BYTE* <span class="arg">buff</span>, <span class="c">/* [OUT] Pointer to the read data buffer */</span>\r | |
| 21 | DWORD <span class="arg">sector</span>, <span class="c">/* [IN] Start sector number */</span>\r | |
| 22 | UINT <span class="arg">count</span> <span class="c">/* [IN] Number of sectros to read */</span>\r | |
| 23 | );\r | |
| 24 | </pre>\r | |
| 25 | </div>\r | |
| 26 | \r | |
| 27 | <div class="para arg">\r | |
| 28 | <h4>Parameters</h4>\r | |
| 29 | <dl class="par">\r | |
| 30 | <dt>pdrv</dt>\r | |
| 31 | <dd>Physical drive number to identify the target device.</dd>\r | |
| 32 | <dt>buff</dt>\r | |
| 289f6a14 | 33 | <dd>Pointer to the first item of the <em>byte array</em> to store read data. Size of read data will be the sector size * <tt class="arg">count</tt> bytes.</dd>\r |
| 53668523 | 34 | <dt>sector</dt>\r |
| 7b78a5a2 | 35 | <dd>Start sector number in 32-bit LBA.</dd>\r |
| 53668523 | 36 | <dt>count</dt>\r |
| 70702af1 | 37 | <dd>Number of sectors to read.</dd>\r |
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38 | </dl>\r |
| 39 | </div>\r | |
| 40 | \r | |
| 41 | \r | |
| 42 | <div class="para ret">\r | |
| 43 | <h4>Return Value</h4>\r | |
| 44 | <dl class="ret">\r | |
| 45 | <dt>RES_OK (0)</dt>\r | |
| 46 | <dd>The function succeeded.</dd>\r | |
| 47 | <dt>RES_ERROR</dt>\r | |
| 289f6a14 | 48 | <dd>An unrecoverable hard error occured during the read operation.</dd>\r |
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49 | <dt>RES_PARERR</dt>\r |
| 50 | <dd>Invalid parameter.</dd>\r | |
| 51 | <dt>RES_NOTRDY</dt>\r | |
| 52 | <dd>The device has not been initialized.</dd>\r | |
| 53 | </dl>\r | |
| 54 | </div>\r | |
| 55 | \r | |
| 56 | \r | |
| 57 | <div class="para desc">\r | |
| 58 | <h4>Description</h4>\r | |
| 289f6a14 | 59 | <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 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 succeeded.</p>\r |
| 70702af1 | 60 | <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 |
| 53668523 | 61 | <ul>\r |
| 7b78a5a2 | 62 | <li>Convert word transfer to byte transfer in this function if needed. - Recommended.</li>\r |
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63 | <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 |
| 64 | <li>On the <tt>f_read(fp, dat, btw, bw)</tt> calls, make sure that <tt>(((UINT)dat & 3) == (f_tell(fp) & 3))</tt> is true. - Word alignment of <tt class="arg">buff</tt> is guaranteed no matter dat is not word aligned.</li>\r | |
| 53668523 | 65 | </ul>\r |
| 289f6a14 | 66 | <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>\r |
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67 | </div>\r |
| 68 | \r | |
| 69 | \r | |
| 70 | <p class="foot"><a href="../00index_e.html">Return</a></p>\r | |
| 71 | </body>\r | |
| 72 | </html>\r |