public FatFileSystem(Cosmos.Hardware.BlockDevice.BlockDevice aDevice)
{
mDevice = aDevice;
byte[] xBPB = mDevice.NewBlockArray(1);
mDevice.ReadBlock(0UL, 1U, xBPB);
UInt16 xSig = xBPB.ToUInt16(510);
if (xSig != 0xAA55)
{
throw new Exception("FAT signature not found.");
}
BytesPerSector = xBPB.ToUInt16(11);
SectorsPerCluster = xBPB[13];
BytesPerCluster = BytesPerSector * SectorsPerCluster;
ReservedSectorCount = xBPB.ToUInt16(14);
NumberOfFATs = xBPB[16];
RootEntryCount = xBPB.ToUInt16(17);
TotalSectorCount = xBPB.ToUInt16(19);
if (TotalSectorCount == 0)
{
TotalSectorCount = xBPB.ToUInt32(32);
}
// FATSz
FatSectorCount = xBPB.ToUInt16(22);
if (FatSectorCount == 0)
{
FatSectorCount = xBPB.ToUInt32(36);
}
//Global.Dbg.Send("FAT Sector Count: " + FatSectorCount);
DataSectorCount = TotalSectorCount - (ReservedSectorCount + (NumberOfFATs * FatSectorCount) + ReservedSectorCount);
// Computation rounds down.
ClusterCount = DataSectorCount / SectorsPerCluster;
// Determine the FAT type. Do not use another method - this IS the official and
// proper way to determine FAT type.
// 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 = xBPB.ToUInt32(44);
}
else
{
RootSector = ReservedSectorCount + (NumberOfFATs * FatSectorCount);
RootSectorCount = (RootEntryCount * 32 + (BytesPerSector - 1)) / BytesPerSector;
}
DataSector = ReservedSectorCount + (NumberOfFATs * FatSectorCount) + RootSectorCount;
}
public FatFileSystem(Cosmos.Hardware.BlockDevice.BlockDevice aDevice)
{
mDevice = aDevice;
byte[] xBPB = mDevice.NewBlockArray(1);
mDevice.ReadBlock(0UL, 1U, xBPB);
UInt16 xSig = xBPB.ToUInt16(510);
if (xSig != 0xAA55)
{
throw new Exception("FAT signature not found.");
}
BytesPerSector = xBPB.ToUInt16(11);
SectorsPerCluster = xBPB[13];
BytesPerCluster = BytesPerSector * SectorsPerCluster;
ReservedSectorCount = xBPB.ToUInt16(14);
NumberOfFATs = xBPB[16];
RootEntryCount = xBPB.ToUInt16(17);
TotalSectorCount = xBPB.ToUInt16(19);
if (TotalSectorCount == 0)
{
TotalSectorCount = xBPB.ToUInt32(32);
}
// FATSz
FatSectorCount = xBPB.ToUInt16(22);
if (FatSectorCount == 0)
{
FatSectorCount = xBPB.ToUInt32(36);
}
//Global.Dbg.Send("FAT Sector Count: " + FatSectorCount);
DataSectorCount = TotalSectorCount - (ReservedSectorCount + (NumberOfFATs * FatSectorCount) + ReservedSectorCount);
// Computation rounds down.
ClusterCount = DataSectorCount / SectorsPerCluster;
// Determine the FAT type. Do not use another method - this IS the official and
// proper way to determine FAT type.
// 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 = xBPB.ToUInt32(44);
}
else
{
RootSector = ReservedSectorCount + (NumberOfFATs * FatSectorCount);
RootSectorCount = (RootEntryCount * 32 + (BytesPerSector - 1)) / BytesPerSector;
}
DataSector = ReservedSectorCount + (NumberOfFATs * FatSectorCount) + RootSectorCount;
}
