// State machine for decoding a message
private void DecodeRxByte(byte Data)
{
switch (_State)
{
// Check to see if first header matches
case FramerState.SearchHeader1:
if (Data == MESSAGE_HEADER1)
{
_State = FramerState.SearchHeader2;
}
break;
// Check to see if second header matches
case FramerState.SearchHeader2:
if (Data == MESSAGE_HEADER2)
{
_State = FramerState.SearchLength;
}
break;
// Record the length
case FramerState.SearchLength:
_Length = Data;
_Data = new List <byte>();
_State = FramerState.SearchData;
break;
// Collect Data for payload
case FramerState.SearchData:
if (_Length > 0)
{
_Data.Add(Data);
_Length--;
// If there is data left, stay in SearchData
// If all data has been collected, next byte will be the checksum
_State = (_Length > 0) ? FramerState.SearchData : FramerState.SearchChecksum;
}
break;
// Calculate checksum
case FramerState.SearchChecksum:
{
byte checksum = 0;
// Add headers and length
checksum += MESSAGE_HEADER1;
checksum += MESSAGE_HEADER2;
checksum += (byte)(_Data.Count & 0xFF);
// Add the command and payload
for (int index = 0; index < _Data.Count; index++)
{
checksum += _Data[index];
}
// Negate checksum
checksum = (byte)((~checksum) & (0xFF));
// Does the checksum match
if (checksum == Data)
{
// Notify upper layer that a full message
// has been received
OnSerialMessageReceived(_Data);
}
}
break;
}
}
// Constructor
public SerialFramer()
{
// Set initial state of decode machine
_State = FramerState.SearchHeader1;
}