/// <summary>
/// Decodes information from a broadcast services data packet.
/// </summary>
/// <param name="packet">The teletext packet to be decoded.</param>
private void DecodeBroadcastServiceData(Packet packet)
{
// Get the designation byte
byte designationByte = Decode.Hamming84(packet.Data[0]);
// Check the designation byte does not have unrecoverable errors, and if it does ignore the packet
if (designationByte == 0xff)
{
return;
}
// Decode the designation code and multiplex status
bool multiplexed = Convert.ToBoolean(designationByte & 0x01);
int designation = designationByte >> 1;
// Check the designation code is 0 (format 1) or 1 (format 2), otherwise ignore the packet
if (designation > 1)
{
return;
}
// Set the multiplexed status
Multiplexed = !multiplexed;
// If the packet is format 1, decode the network identification code
if (designation == 0)
{
byte[] networkID = { packet.Data[7], packet.Data[8] };
NetworkID = BitConverter.ToString(networkID).Replace("-", "");
}
// Get the status display
byte[] statusCharacters = new byte[packet.Data.Length - 20];
for (int i = 20; i < packet.Data.Length; i++)
{
statusCharacters[i - 20] = Decode.OddParity(packet.Data[i]);
}
StatusDisplay = Encoding.ASCII.GetString(statusCharacters);
// Decode the digits for the inital page number
byte pageUnits = Decode.Hamming84(packet.Data[1]);
byte pageTens = Decode.Hamming84(packet.Data[2]);
// Decode the bytes for the initial subcode
byte subcode1 = Decode.Hamming84(packet.Data[3]);
byte subcode2 = Decode.Hamming84(packet.Data[4]);
byte subcode3 = Decode.Hamming84(packet.Data[5]);
byte subcode4 = Decode.Hamming84(packet.Data[6]);
// If the subcode bytes containing the magazine number contains errors, stop processing
if (subcode2 == 0xff || subcode4 == 0xff)
{
return;
}
// If the page number digits don't contain errors, set the initial page number
if (pageUnits != 0xff && pageTens != 0xff)
{
// Get the magazine number, changing 0 to 8
byte magazineNumber = (byte)((subcode2 >> 3) | ((subcode4 & 0x0C) >> 1));
if (magazineNumber == 0)
{
magazineNumber = 8;
}
// Set the initial page number
InitialPage = magazineNumber.ToString("X1") + ((pageTens << 4) | pageUnits).ToString("X2");
}
// If the remaining subcode bytes don't contain any errors, set the subcode
if (subcode1 != 0xff && subcode3 != 0xff)
{
byte[] fullSubcode = { (byte)(((subcode4 & 0x03) << 4) | subcode3), (byte)(((subcode2 & 0x07) << 4) | subcode1) };
InitialSubcode = BitConverter.ToString(fullSubcode).Replace("-", "");
}
}
