/// <summary>
/// Parse a BIOS Parameter Block from a stream
/// </summary>
/// <param name="reader">A binary reader around the stream</param>
/// <param name="offset">The offset in the stream of the BPB</param>
/// <returns>A BIOS Parameter block</returns>
public static BiosParameterBlock Parse(BinaryReader reader, long offset)
{
reader.BaseStream.Seek(offset, SeekOrigin.Begin); //BPB offset
var bpb = new BiosParameterBlock
{
BytesPerLogicalSector = reader.ReadUInt16(),
LogicalSectorsPerCluster = reader.ReadByte(),
ReservedLogicalSectors = reader.ReadUInt16(),
NumberOfFATs = reader.ReadByte(),
RootDirectoryEntries = reader.ReadUInt16(),
TotalLogicalSectors = reader.ReadUInt16(),
MediaDescriptor = reader.ReadByte(),
LogicalSectorsPerFAT = reader.ReadUInt16()
};
//Parsing a standard BPB
if (offset == 0x0B)
{
bpb.PhysicalSectorsPerTrack = reader.ReadUInt16();
bpb.NumberOfHeads = reader.ReadUInt16();
if (bpb.TotalLogicalSectors != 0)
{
bpb.HiddenSectors = reader.ReadUInt16();
reader.BaseStream.Seek(6, SeekOrigin.Current);
}
else
{
bpb.HiddenSectors = reader.ReadUInt32();
bpb.TotalLogicalSectors = reader.ReadUInt32();
}
}
//Parsing an Apricot BPB, which doesn't have the number of heads and SPT, so we have to make some manual adjustments
else if (offset == 0x50)
{
if (bpb.MediaDescriptor == 0xFC) //315k
{
bpb.NumberOfHeads = 1;
bpb.PhysicalSectorsPerTrack = 70;
}
else if (bpb.MediaDescriptor == 0xFE) //720k
{
bpb.NumberOfHeads = 2;
bpb.PhysicalSectorsPerTrack = 80;
}
}
if (!bpb.Validate())
{
throw new InvalidDataException("At least one of BPB parameters is 0");
}
uint tracks = (uint)(bpb.TotalLogicalSectors / bpb.NumberOfHeads / bpb.PhysicalSectorsPerTrack);
// TODO: This probably needs reviewing to better check BPB params match the correct size
if (tracks == 0)
{
throw new InvalidDataException("BPB paramaters don't match image size");
}
// Parsing a standard BPB, read boot sector
if (offset == 0x0B)
{
long endOffset = reader.BaseStream.Position;
reader.BaseStream.Seek(0, SeekOrigin.Begin);
bpb.BootJump = reader.ReadBytes(3);
bpb.OemId = new string(reader.ReadChars(8)).TrimEnd(' ').ToUpper();
reader.BaseStream.Seek(endOffset, SeekOrigin.Begin);
}
if (bpb.LogicalSectorsPerFAT == 0)
{
// This could be a FAT32 BPB.
return(Fat32BiosParameterBlock.ContinueParsing(bpb, reader) ?? throw new InvalidDataException("FAT size is 0"));
}
else
{
//So far, the BPB seems to be OK, so try to read it further as a DOS 4.0 BPB.
return(ExtendedBiosParameterBlock.ContinueParsing(bpb, reader) ?? bpb);
}
}
