除了支持长文件名外，其实FAT32基本上只是在族（cluster)的定义上加长为32bit而已。反过来，FAT32实际上简化了整个结构：它的根目录区被简化为一个族。所以
对FAT32文件系统的根目录操作不必另眼看待，可与普通子目录的操作相同。
以下是一个对FAT32读操作的实例 （在PIC18F2520上实现）：
#include <string.h>
#include "define.h"
#include "mmcspi.h"
#include "mmcfile.h"
#include "fat32.h"
#include "lcd3310.h"
#define fileStartCluster(dir) ((dir->startClusterHi << 16) | dir->startClusterLo)
static FileDesc_t *FAT32_FindFileInSubDir (unsigned long cluster, unsigned int *cntptr, unsigned char depth);
static void FAT32_searchFileInSubDir (unsigned long cluster, unsigned int *cnt, unsigned char depth);
///////////////////////////////////////////////////////////////////////
char FAT32_InitEntry (BootSector_t_FAT32 *pp)
{
if ( pp->numOfFAT == 2 && pp->rootEntries == 0 &&
pp->sectorPerCluster && pp->sectorSize == MMC_SECTOR_SIZE )
{
FILE_entry.sectorPerCluster = pp->sectorPerCluster;
FILE_entry.sectorPerFAT32 = pp->numOfSectorPerFAT;
// FILE_entry.totalSectors = pp->totalSectors; // size of volume
// FILE_entry.startOfFileSys = FILE_entry.startSector + pp->sectorOfFileSysInfo;
FILE_entry.fatStart = FILE_entry.startSector + pp->reserveSectors; // fat area start sector #
// FILE_entry.rootStart = FILE_entry.fatStart + FILE_entry.sectorPerFAT32 * FILE_entry.numOfFAT;
FILE_entry.dataStart = FILE_entry.fatStart + FILE_entry.sectorPerFAT32 * 2; // data area start sector #
FILE_entry.startClusterOfRoot= pp->clusterOfRootDir; // root directory start cluster #
/*
char buf[20];
ltoa (FILE_entry.fatStart, buf, 10); LCD_write_string (0, 3, buf);
ltoa (FILE_entry.dataStart, buf, 10); LCD_write_string (0, 4, buf);
ltoa (pp->clusterOfRootDir, buf, 10); LCD_write_string (0, 5, buf);
for(;;);
*/
return FILE_OK;
}
return FILE_ERR_FMT;
}
///////////////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////
FileDesc_t * FAT32_ReturnFileHandle (DirEntry_t_FAT32 *dir)
{
memcpy (fileDesc.fileName, dir->fileName, 11); // get filename+ext
fileDesc.size = dir->fileSize; // get file size
fileDesc.cluster = fileStartCluster(dir); // get file (start) cluster)
fileDesc.sector = 0;
return &fileDesc;
}
///////////////////////////////////////////////////////////////////////////////
//
// now it supports N-level directory structure ... (Ha-Ha!) May, 2004
//
///////////////////////////////////////////////////////////////////////////////
FileDesc_t *FAT32_FindFile (unsigned int index)
{
return FAT32_FindFileInSubDir (FILE_entry.startClusterOfRoot, &index, 0);
}
///////////////////////////////////////////////////////////////////////////////
#pragma recursive_function
static FileDesc_t *FAT32_FindFileInSubDir (unsigned long cluster, unsigned int *cntptr, unsigned char depth)
{
subDirDesc.cluster = cluster;
subDirDesc.sector = 0;
while ( FAT32_readFileSector (&subDirDesc) != NULL )
{
unsigned int j;
FileDesc_t *fdes;
for (j = 0; j < MMC_SECTOR_SIZE; j += DIR_ENTRY_SIZE)
{
DirEntry_t_FAT32 *dir = (DirEntry_t_FAT32 *)&FILE_tempBuf[j];
switch ( FILE_EntryType (dir) )
{
case MP3_FILE:
(*cntptr)--; // it's an MP3 file
if ( *cntptr == 0 )
return FAT32_ReturnFileHandle (dir);
break;
case SUB_DIR: // it's a sub-directory!
if ( depth < MAX_DIR_DEPTH )
{
// save the cluster/sector
unsigned long this_cluster= subDirDesc.cluster;
unsigned char this_sector = subDirDesc.sector;
// recursive searching for sub-directory
fdes = FAT32_FindFileInSubDir (fileStartCluster(dir), cntptr, depth+1);
if ( fdes != NULL )
return fdes;
// restore the cluster/sector
subDirDesc.cluster= this_cluster;
subDirDesc.sector = this_sector - 1;
FAT32_readFileSector (&subDirDesc); // read back the sector
}
break;
}
}
}
return NULL;
}
///////////////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////
static unsigned long FAT32_GetDataSector (unsigned long cluster)
{
return FILE_entry.dataStart + (cluster - FILE_entry.startClusterOfRoot) * FILE_entry.sectorPerCluster;
}
#define FILE_ClusterFatOffset(cluster) ((cluster & 0x7f) << 2)
///////////////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////
static unsigned long FAT32_NextCluster (unsigned long cluster)
{
unsigned long sector;
//#pragma short_branch
if ( cluster < 2 || cluster >= 0x0ffffff0 )
return 0xffffffff;
// FAT32: 128 cluster items per sector
sector = FILE_entry.fatStart + cluster / 128;
if ( MMC_ReadSector (FILE_tempBuf, sector) == MMC_OK )
{
unsigned int offset = FILE_ClusterFatOffset (cluster);
return *((unsigned long *)&FILE_tempBuf[offset]);
}
return 0xffffffff;
}
///////////////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////
unsigned char *FAT32_readFileSector (FileDesc_t *file)
{
if ( file->sector >= FILE_entry.sectorPerCluster )
{
file->cluster = FAT32_NextCluster (file->cluster);
file->sector = 0;
}
if ( file->cluster >= 0x0ffffff0 )
return NULL;
if ( file->sector == 0 )
file->startSector = FAT32_GetDataSector (file->cluster);
unsigned long sector = file->startSector + file->sector++;
if ( MMC_ReadSector (FILE_tempBuf, sector) != MMC_OK )
return NULL;
return FILE_tempBuf;
}
///////////////////////////////////////////////////////////////////////////////
/*
only get data sector number, not read the sector data!
*/
char FAT32_nextFileSector (FileDesc_t *file)
{
if ( file->sector >= FILE_entry.sectorPerCluster )
{
file->cluster = FAT32_NextCluster (file->cluster);
file->sector = 0;
}
if ( file->cluster >= 0xffffff0 )
return 0;
if ( file->sector == 0 )
file->startSector = FAT32_GetDataSector (file->cluster);
file->sector++;
return -1;
}
///////////////////////////////////////////////////////////////////////////////
unsigned int FAT32_searchMP3Files (void)
{
unsigned int cnt = 0;
FAT32_searchFileInSubDir (FILE_entry.startClusterOfRoot, &cnt, 0);
return cnt;
}
///////////////////////////////////////////////////////////////////////////////
#pragma recursive_function
static void FAT32_searchFileInSubDir (unsigned long cluster, unsigned int *cnt, unsigned char depth)
{
subDirDesc.cluster = cluster;
subDirDesc.sector = 0;
while ( FAT32_readFileSector (&subDirDesc) != NULL )
{
unsigned int i;
for (i = 0; i < MMC_SECTOR_SIZE; i += DIR_ENTRY_SIZE)
{
DirEntry_t_FAT32 *dir = &FILE_tempBuf;
switch ( FILE_EntryType (dir) )
{
case MP3_FILE:
(*cnt)++; // it's an MP3 file
break;
case SUB_DIR: // it's a sub-directory!
if ( depth < MAX_DIR_DEPTH )
{
// save the cluster/sector
unsigned long this_cluster= subDirDesc.cluster;
unsigned char this_sector = subDirDesc.sector;
// recursive searching for sub-directory
FAT32_searchFileInSubDir (fileStartCluster (dir), cnt, depth+1);
// restore the cluster/sector
subDirDesc.cluster = this_cluster;
subDirDesc.sector = this_sector - 1;
FAT32_readFileSector (&subDirDesc);
}
break;
}
}
}
}
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