filesys_8c.html

MP3 Player Source Code

Referenced by <a class="el" href="filesys_8c-source.html#l00248">ScanForFreeSector()</a>.
<p>
<pre class="fragment"><div>00085                                                       {
00086   <span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> entryNumber; <span class="comment">/* entry number inside page */</span>
00087 
00088   <span class="keywordflow">if</span> (!<a class="code" href="filesys_8h.html#a0">IS_FAT_32</a>){ <span class="comment">//FAT16</span>
00089     entryNumber = clusterNumber &amp; 0xff; 
00090     clusterNumber &gt;&gt;= 8; 
00091   }<span class="keywordflow">else</span>{ <span class="comment">//FAT32</span>
00092     entryNumber = clusterNumber &amp; 0x7f;
00093     clusterNumber &gt;&gt;= 7; 
00094   }
00095   clusterNumber += <a class="code" href="filesys_8c.html#a2">fatStart</a>;
00096   <span class="keywordflow">if</span> (<a class="code" href="buffer_8c.html#a2">sectorAddress</a>.<a class="code" href="unionAddress.html#o0">l</a> != clusterNumber){
00097     <a class="code" href="buffer_8c.html#a2">sectorAddress</a>.<a class="code" href="unionAddress.html#o0">l</a> = clusterNumber;
00098     <a class="code" href="storage_8h.html#a2">ReadDiskSector</a>(<a class="code" href="buffer_8c.html#a2">sectorAddress</a>.<a class="code" href="unionAddress.html#o0">l</a>);
00099   }
00100   <span class="keywordflow">if</span> (<a class="code" href="filesys_8h.html#a0">IS_FAT_32</a>){
00101     clusterNumber=<a class="code" href="buffer_8c.html#a0">diskSect</a>.<a class="code" href="unionDiskBlock.html#o4">Fat32Table</a>[entryNumber];
00102     <span class="keywordflow">return</span> clusterNumber;
00103   }
00104   <span class="keywordflow">if</span> ((clusterNumber=<a class="code" href="buffer_8c.html#a0">diskSect</a>.<a class="code" href="unionDiskBlock.html#o3">Fat16Table</a>[entryNumber])==0xffff) <span class="keywordflow">return</span> 0xffffffff;
00105   <span class="keywordflow">return</span> clusterNumber;
00106 }
</div></pre>
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<a class="anchor" name="a18" doxytag="filesys.c::GetNextSector" ></a><p>
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          <td class="md" nowrap valign="top"> unsigned long GetNextSector           </td>
          <td class="md" valign="top">(&nbsp;</td>
          <td class="md" nowrap valign="top">unsigned long&nbsp;</td>
          <td class="mdname1" valign="top" nowrap> <em>currentSector</em>          </td>
          <td class="md" valign="top">&nbsp;)&nbsp;</td>
          <td class="md" nowrap></td>
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<p>
Calculate next sector from currentSector. 
<p>
Return sector address with MSB set if end of file.<p>
This is the essence of FAT filesystem: traversing through the file allocation table to scan for cluster chains. 
<p>
Definition at line <a class="el" href="filesys_8c-source.html#l00303">303</a> of file <a class="el" href="filesys_8c-source.html">filesys.c</a>.
<p>
References <a class="el" href="unionAddress.html#o1">Address::b</a>, <a class="el" href="buffer_8h-source.html#l00131">Address::B::b0</a>, <a class="el" href="buffer_8h-source.html#l00132">Address::B::b1</a>, <a class="el" href="buffer_8h-source.html#l00134">Address::B::b3</a>, <a class="el" href="filesys_8c-source.html#l00029">dataStart</a>, <a class="el" href="buffer_8c-source.html#l00010">diskSect</a>, <a class="el" href="buffer_8h-source.html#l00114">DiskBlock::Fat16Table</a>, <a class="el" href="buffer_8h-source.html#l00117">DiskBlock::Fat32Table</a>, <a class="el" href="filesys_8c-source.html#l00032">fatSectorsPerCluster</a>, <a class="el" href="filesys_8c-source.html#l00021">fatStart</a>, <a class="el" href="filesys_8h-source.html#l00015">IS_FAT_32</a>, <a class="el" href="buffer_8h-source.html#l00129">Address::l</a>, <a class="el" href="storage_8c-source.html#l00110">ReadDiskSector()</a>, and <a class="el" href="buffer_8c-source.html#l00015">sectorAddress</a>.
<p>
Referenced by <a class="el" href="filesys_8c-source.html#l00541">LoadNextSector()</a>, and <a class="el" href="filesys_8c-source.html#l00610">OpenFile()</a>.
<p>
<pre class="fragment"><div>00303                                                         {
00304   <a class="code" href="unionAddress.html">addressType</a> fatSector;
00305   <span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> entryNumber;
00306   
00307   <span class="comment">/* how manyth sector from start of data area -&gt; fatsector */</span>
00308   fatSector.<a class="code" href="unionAddress.html#o0">l</a> = currentSector - <a class="code" href="filesys_8c.html#a4">dataStart</a>;
00309   
00310   <span class="comment">/* Check for cluster boundary */</span>
00311   <span class="comment">/* if we're not in cluster boundary then return currentsector + 1 */</span>
00312   <span class="keywordflow">if</span> ((fatSector.<a class="code" href="unionAddress.html#o1">b</a>.<a class="code" href="structAddress_1_1B.html#o0">b0</a> + 1) % <a class="code" href="filesys_8c.html#a5">fatSectorsPerCluster</a>){
00313     <span class="keywordflow">return</span> currentSector + 1;
00314   }
00315   
00316   <span class="comment">/* is the value negative? then return currentSector + 1 */</span>
00317   <span class="keywordflow">if</span> (fatSector.<a class="code" href="unionAddress.html#o1">b</a>.<a class="code" href="structAddress_1_1B.html#o3">b3</a> &amp; 0x80) {
00318     <span class="keywordflow">return</span> currentSector + 1;
00319   }    
00320 
00321   <span class="comment">/* The trivial conditions are not met, we actually do need to </span>
00322 <span class="comment">     look up the next sector info from FAT tables in the disk.*/</span>
00323 
00324   <span class="comment">/* convert fatSector from CurrentSectorN to currentClusterN */</span>
00325   fatSector.<a class="code" href="unionAddress.html#o0">l</a> /= <a class="code" href="filesys_8c.html#a5">fatSectorsPerCluster</a>;
00326 
00327   <span class="comment">/* calculate which page (fatSector) and entry of FAT table correspond</span>
00328 <span class="comment">     to current sector */</span>
00329    
00330   <span class="keywordflow">if</span> (!<a class="code" href="filesys_8h.html#a0">IS_FAT_32</a>){ <span class="comment">//FAT16</span>
00331     entryNumber = fatSector.<a class="code" href="unionAddress.html#o1">b</a>.<a class="code" href="structAddress_1_1B.html#o0">b0</a>; <span class="comment">/* 256 entries / page in FAT16 table */</span>
00332     fatSector.<a class="code" href="unionAddress.html#o0">l</a> &gt;&gt;= 8; <span class="comment">/* Divide by 256 (n of entries/page in FAT32 table */</span>
00333   }<span class="keywordflow">else</span>{ <span class="comment">//FAT32</span>
00334     entryNumber =(fatSector.<a class="code" href="unionAddress.html#o1">b</a>.<a class="code" href="structAddress_1_1B.html#o0">b0</a> &amp; 0x7f); <span class="comment">/* 128 entries/page in FAT32 tbl */</span>
00335     fatSector.<a class="code" href="unionAddress.html#o0">l</a> &gt;&gt;= 7; <span class="comment">/* Divide by 128 (n of entries/sector in FAT32 table */</span>
00336   }
00337   
00338   <span class="comment">/* Get sector address for the needed page */</span>
00339   fatSector.<a class="code" href="unionAddress.html#o0">l</a> += <a class="code" href="filesys_8c.html#a2">fatStart</a>;
00340   
00341   <span class="comment">/* Load (if needed) table page from disk */</span>
00342   <span class="keywordflow">if</span> (<a class="code" href="buffer_8c.html#a2">sectorAddress</a>.<a class="code" href="unionAddress.html#o0">l</a> != fatSector.<a class="code" href="unionAddress.html#o0">l</a>){
00343     <a class="code" href="buffer_8c.html#a2">sectorAddress</a>.<a class="code" href="unionAddress.html#o0">l</a> = fatSector.<a class="code" href="unionAddress.html#o0">l</a>; <span class="comment">/* (not needed because mmc.c does this) */</span>
00344     <a class="code" href="storage_8h.html#a2">ReadDiskSector</a>(fatSector.<a class="code" href="unionAddress.html#o0">l</a>);
00345     
00346     ConsolePutChar(<span class="charliteral">'n'</span>);
00347     
00348     
00349   }
00350   <span class="comment">/* Now there should be correct FAT entry page in memory... */</span>
00351   
00352   <span class="keywordflow">if</span> (!<a class="code" href="filesys_8h.html#a0">IS_FAT_32</a>){ <span class="comment">//FAT16</span>
00353     fatSector.<a class="code" href="unionAddress.html#o0">l</a> = <a class="code" href="buffer_8c.html#a0">diskSect</a>.<a class="code" href="unionDiskBlock.html#o3">Fat16Table</a>[entryNumber];
00354     <span class="comment">/* Check for FAT16 end-of-file condition */</span>
00355     <span class="keywordflow">if</span> ((fatSector.<a class="code" href="unionAddress.html#o1">b</a>.<a class="code" href="structAddress_1_1B.html#o1">b1</a> == 0xff) &amp;&amp; (fatSector.<a class="code" href="unionAddress.html#o1">b</a>.<a class="code" href="structAddress_1_1B.html#o0">b0</a> == 0xff)){
00356       <span class="comment">/* End of file */</span>
00357       fatSector.<a class="code" href="unionAddress.html#o1">b</a>.<a class="code" href="structAddress_1_1B.html#o3">b3</a> = 0xff; <span class="comment">/* return a large value (fat32 compatible) */</span>
00358       <span class="keywordflow">return</span> fatSector.<a class="code" href="unionAddress.html#o0">l</a>;
00359     }
00360   }<span class="keywordflow">else</span>{ <span class="comment">//FAT32</span>
00361     fatSector.<a class="code" href="unionAddress.html#o0">l</a> = <a class="code" href="buffer_8c.html#a0">diskSect</a>.<a class="code" href="unionDiskBlock.html#o4">Fat32Table</a>[entryNumber] &amp; 0x0fffffff;
00362     <span class="comment">/* Check for FAT32 end-of-file condition */</span>
00363     <span class="keywordflow">if</span> ((fatSector.<a class="code" href="unionAddress.html#o1">b</a>.<a class="code" href="structAddress_1_1B.html#o3">b3</a>&amp;0x08) <span class="comment">//Quick test</span>
00364         &amp;&amp; (fatSector.<a class="code" href="unionAddress.html#o0">l</a>&gt;0x0ffffff0)){ <span class="comment">//Complete test</span>
00365       <span class="comment">/* End of file */</span>
00366       <span class="keywordflow">return</span> 0xffffffff; <span class="comment">/* return EOF*/</span>
00367     }
00368   }
00369   
00370 
00371   <span class="comment">/* now fatSector.l contains the proper next cluster value */</span>
00372 
00373   fatSector.<a class="code" href="unionAddress.html#o0">l</a> *= <a class="code" href="filesys_8c.html#a5">fatSectorsPerCluster</a>;
00374   <span class="comment">/* now fatSector.l contains the next sector value */</span>
00375 
00376   fatSector.<a class="code" href="unionAddress.html#o0">l</a> += <a class="code" href="filesys_8c.html#a4">dataStart</a>;
00377   <span class="comment">/* now fatSector.l contains the proper absolute sector address */</span>
00378 
00379   <span class="keywordflow">return</span> fatSector.<a class="code" href="unionAddress.html#o0">l</a>;
00380 }
</div></pre>
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