private bool IsValidChecksum()
{
ushort checkSum = GetChecksum(dataLength - 2);
return(checkSum == Crc16.ComputeChecksum(buffer, 1, dataLength - 2));
}
public bool Read(byte data)
{
if (position == 0 && data != 0x7E)
{
// we haven't started yet, wait for the start flag (no need to capture any data yet)
return(false);
}
else
{
// We have completed reading of one package, so clear and be ready for the next
if (dataLength > 0 && position >= dataLength + 2)
{
Clear();
}
// Check if we're about to run into a buffer overflow
if (position >= buffer.Length)
{
Clear();
}
// Check if this is a second start flag, which indicates the previous one was a stop from the last package
if (position == 1 && data == 0x7E)
{
// just return, we can keep the one byte we had in the buffer
return(false);
}
// We have started, so capture every byte
buffer[position++] = data;
if (position == 1)
{
// This was the start flag, we're not done yet
return(false);
}
else if (position == 2)
{
// Capture the Frame Format Type
frameFormatType = (byte)(data & 0xF0);
if (!IsValidFrameFormat(frameFormatType))
{
Clear();
}
return(false);
}
else if (position == 3)
{
// Capture the length of the data package
dataLength = ((buffer[1] & 0x0F) << 8) | buffer[2];
return(false);
}
else if (destinationAddress == null)
{
// Capture the destination address
destinationAddress = GetAddress(3);
if (destinationAddress?.Length > 3)
{
Clear();
}
return(false);
}
else if (sourceAddress == null)
{
// Capture the source address
sourceAddress = GetAddress(3 + destinationAddress.Length);
if (sourceAddress?.Length > 3)
{
Clear();
}
return(false);
}
else if (position == 4 + destinationAddress.Length + sourceAddress.Length + 2)
{
// Verify the header checksum
var headerChecksum = GetChecksum(position - 3);
if (headerChecksum != Crc16.ComputeChecksum(buffer, 1, position - 3))
{
Clear();
}
return(false);
}
else if (position == dataLength + 1)
{
// Verify the data package checksum
var checksum = GetChecksum(position - 3);
if (checksum != Crc16.ComputeChecksum(buffer, 1, position - 3))
{
Clear();
}
return(false);
}
else if (position == dataLength + 2)
{
// We're done, check the stop flag and signal we're done
if (data == 0x7E)
{
return(true);
}
else
{
Clear();
return(false);
}
}
}
return(false);
}