public override int ProcessBytes(byte[] bytes, int offset, int size)
{
N2kHeader n2kHeader = new N2kHeader(bytes[0], bytes[1], bytes[2], bytes[3]);
byte[] n2kData = new byte[size - 4];
Array.Copy(bytes, 4, n2kData, 0, size - 4);
N2kFrame n2kFrame = new N2kFrame(n2kHeader, n2kData, DateTime.Now);
OnFrameCreated(n2kFrame);
return(size);
}
// Private methods
private void ProcessN2kMessage(ActisenseMessage msg)
{
/* This N2kDataReceived message goes:
* [0] Priority
* [1] PGN LSB=Least Significant Byte
* [2] PGN Middle Byte
* [3] PGN MSB=MostSignificant Byte
* [4] Destination
* [5] Source
* [6,7,8,9] Time stamp, LSB...MSB
* [10] N2k payload length
* [11, 12, ...] N2k payload (always 8 bytes in data seen so far)
*/
byte[] payload = msg.MessagePayload;
byte Priority = payload[0];
int PGN = payload[1] + (payload[2] << 8) + (payload[3] << 16);
byte Destination = payload[4];
byte Source = payload[5];
uint ms = BitConverter.ToUInt32(payload, 6);
// TODO: Work out what the Actisense is transmitting in its time-stamp field
// as the number of milliseconds appears to go down as well as up (according to a user report)
// Note that the Actisense clock appears to be reset when the unit is reset by software,
/* as indicated by the following R(read)/W(rite) sequence of commands
* Clock 4 bytes
* W: 10 2 A1 1 13 4B 10 3
* R: 10 2 93 13 2 2 FD 1 FF 3A 66 9F 0 0 8 FF 3 3 69 0 FA FF FF AC 10 3
* R: 10 2 A0 0E 13 1 0E 0 FA A4 1 0 0 0 0 0 0 1 90 10 3
* W: 10 2 A1 3 13 0 0 49 10 3
* R: 10 2 A0 0E 13 1 0E 0 FA A4 1 0 0 0 0 0 0 0 91 10 3
* W: 10 2 A1 1 10 10 4E 10 3
* R: 10 2 93 13 2 12 F1 1 FF 3A 98 9F 0 0 8 FF 0 0 FF 7F FF 7F FD E4 10 3
* R: 10 2 A0 22 10 10 1 0E 0 FA A4 1 0 0 0 0 0 6D 0 3C 9C 25 93 67 8 3C 9C 2A 93 67 0 BB AF 0 0 3 0 0 0 AB 10 3
* W: 10 2 A1 2 4C 2 0F 10 3 <- some sort of reset?
* R: 10 2 A0 0D 4C 1 0E 0 FA A4 1 0 0 0 0 0 2 57 10 3
* W: 10 2 A1 1 13 4B 10 3 <- some sort of reset?
* R: 10 2 A0 0F F0 1 0E 0 FA A4 1 0 0 0 0 0 67 8 0 44 10 3
* R: 10 2 93 13 2 12 F1 1 FF 3A 2D 0 0 0 8 FF 0 0 FF 7F FF 7F FD EE 10 3
*/
// For now, we just use the computer's clock (and so don't get millisecond accuracy)
DateTime thisTime;
thisTime = DateTime.Now;
//if (firstArrived)
//{
// // Check for rollover.
// if (ms < lastMs)
// baseTime = baseTime.AddMilliseconds(uint.MaxValue); // being 8.1715 years
// thisTime = baseTime.AddMilliseconds(ms);
//}
//else
//{
// firstArrived = true;
// thisTime = DateTime.Now;
// baseTime = thisTime.AddMilliseconds(-ms);
//}
//lastMs = ms;
int N2kDataLength = payload[10];
byte[] N2kData = new byte[N2kDataLength];
Array.Copy(payload, 11, N2kData, 0, N2kDataLength);
N2kHeader Header = new N2kHeader(Priority, PGN, Destination, Source);
N2kFrame frame = new N2kFrame(Header, N2kData, thisTime);
OnFrameCreated(frame);
}
// Public methods
public static int PackFrame(N2kFrame n2kFrame, byte[] buffer)
{
/* [0] Message Protocol: 0x93 = N2kDataReceived
* [1] Message body length (number of bytes 2, 3, ..., up to last byte before CRC)
* [2] Priority
* [3] PGN LSB=Least Significant Byte
* [4] PGN Middle Byte
* [5] PGN MSB=MostSignificant Byte
* [6] Destination
* [7] Source
* [8,9,10,11] Time stamp, LSB...MSB
* [12] N2k payload length
* [13, 14, ..., 13+[12]=20 ] N2k payload (always 8 bytes in data seen so far)
* [21] CRC byte, chosen so that the sum over all bytes is 0 (mod 256).
*/
// TODO : Test sending
// - confirm CRC is generated correctly
N2kHeader n2kHeader = n2kFrame.Header;
buffer[0] = Escape;
buffer[1] = StartOfText;
buffer[2] = N2kDataReceived; // TODO : What should this be ?
int pgn = n2kHeader.PGN;
byte pgnLSB = (byte)(pgn & 0xFF);
pgn >>= 8;
byte pgnMDB = (byte)(pgn & 0xFF);
pgn >>= 8;
byte pgnMSB = (byte)(pgn & 0xFF);
buffer[4] = n2kHeader.PGNPriority;
buffer[5] = pgnLSB;
buffer[6] = pgnMDB;
buffer[7] = pgnMSB;
buffer[8] = n2kHeader.PGNDestination;
buffer[9] = n2kHeader.PGNSource;
// Set timestamp bytes [10, 11, 12, 13]
Array.Copy(BitConverter.GetBytes(DateTime.Now.Millisecond), 0, buffer, 10, 4);
// Byte 14 : Length of n2k data
buffer[14] = (byte)n2kFrame.Data.Length; // N2k data length : Bytes [15, CRCbyte)
byte msgIdx = 15;
for (int i = 0; i < n2kFrame.Data.Length; i++)
{
if (n2kFrame.Data[i] == Escape)
{
buffer[msgIdx++] = Escape;
buffer[msgIdx++] = Escape;
}
else
{
buffer[msgIdx++] = n2kFrame.Data[i];
}
}
int byteSum = 0;
for (int i = 2; i < msgIdx; i++)
{
byteSum += buffer[i];
}
byteSum %= 256;
buffer[msgIdx++] = (byte)((byteSum == 0) ? 0 : (256 - byteSum));
buffer[3] = (byte)(msgIdx - 5); // Message length : Bytes [4, CRCbyte)
buffer[msgIdx++] = Escape;
buffer[msgIdx++] = EndOfText;
return(msgIdx);
}
