/// <summary>
/// Gets the EOF value for the specified FAT type.
/// </summary>
/// <param name="aFATType">The FAT type.</param>
/// <returns>The EOF value.</returns>
public static UInt32 GetFATEntryEOFValue(FATTypeEnum aFATType)
{
if (aFATType == FATTypeEnum.FAT12)
{
return 0x0FF8;
}
else if (aFATType == FATTypeEnum.FAT16)
{
return 0xFFF8;
}
else
{
return 0x0FFFFFF8;
}
}
/// <summary>
/// Initializes a new FAT file system from the specified partition.
/// </summary>
/// <param name="aPartition">The partition on which the file system resides.</param>
/// <remarks>
/// You should check IsValid after creating a new FAT file system to check a valid FAT
/// file system has been detected.
/// </remarks>
public FATFileSystem(Partition aPartition)
: base(aPartition)
{
//Create an array to store the BPB data.
byte[] BPBData = thePartition.NewBlockArray(1);
//Load the BIOS Parameter Block - the first sector of the partition.
thePartition.ReadBlock(0UL, 1U, BPBData);
//Check the top two bytes for the signature
if (BPBData[510] != 0x55 ||
BPBData[511] != 0xAA)
{
//If they are wrong, this is not a valid FAT file system.
return;
}
//The signature is the only thing we can check to determine if this is FAT
// so we must now assume this is a valid FAT file system.
isValid = true;
//Load or calculate the various bits of data required to use a FAT file system.
BytesPerSector = ByteConverter.ToUInt16(BPBData, 11);
SectorsPerCluster = BPBData[13];
BytesPerCluster = BytesPerSector * SectorsPerCluster;
ReservedSectorCount = ByteConverter.ToUInt16(BPBData, 14);
NumberOfFATs = BPBData[16];
RootEntryCount = ByteConverter.ToUInt16(BPBData, 17);
TotalSectorCount = ByteConverter.ToUInt16(BPBData, 19);
if (TotalSectorCount == 0)
{
TotalSectorCount = ByteConverter.ToUInt32(BPBData, 32);
}
//Valid for FAT12/16
//Invalid for FAT32, SectorCount always 0 in this field.
FATSectorCount = ByteConverter.ToUInt16(BPBData, 22);
if (FATSectorCount == 0)
{
//FAT32 has a different, larger field for sector count
FATSectorCount = ByteConverter.ToUInt32(BPBData, 36);
}
DataSectorCount = TotalSectorCount - (ReservedSectorCount + (NumberOfFATs * FATSectorCount));
// Computation rounds down.
ClusterCount = DataSectorCount / SectorsPerCluster;
// Determine the FAT type.
//This is the official and proper way to determine FAT type - don't alter it.
// - If you want to implement some hack, add a new FAT file system class /
// implementation and add it to the appropriate partition initialisation
// methods
// Comparisons are purposefully < and not <=
// FAT16 starts at 4085, FAT32 starts at 65525
if (ClusterCount < 4085)
{
FATType = FATTypeEnum.FAT12;
}
else if (ClusterCount < 65525)
{
FATType = FATTypeEnum.FAT16;
}
else
{
FATType = FATTypeEnum.FAT32;
}
if (FATType == FATTypeEnum.FAT32)
{
RootCluster = ByteConverter.ToUInt32(BPBData, 44);
}
else
{
RootSector = ReservedSectorCount + (NumberOfFATs * FATSectorCount);
RootSectorCount = (RootEntryCount * 32 + (BytesPerSector - 1)) / BytesPerSector;
}
DataSector = ReservedSectorCount + (NumberOfFATs * FATSectorCount) + RootSectorCount;
}
