/// <summary>
/// Function used for packet transmission in xmodem protocol
/// </summary>
private static void TransmitPacket(Sym mode)
{
if (mode == Sym.NAK)
{
PortWriteByte((byte)Sym.SOH); // Sending StartOfHeader symbol for packet initialization
//Console.WriteLine("SOH")
}
else if (mode == Sym.C)
{
PortWriteByte((byte)Sym.C); // Sending C symbol for CRC packet initialization
}
else
{
throw new Exception("Bad protocol mode passed");
}
if (seq == 0)
{
seq = 1;
}
PortWriteByte(seq); // Sending sequence number
//Console.WriteLine("seq: " + seq);
PortWriteByte((byte)(255 - (255 & seq))); // Calculating and sending the complement of seq
//Console.WriteLine("cmpl: " + (byte)(255 - seq));
seq++; // Increasing the sequence number
// Copying 128 bytes of data to transmit
// If there is any underflow, the following bytes will be left null (0)
byte[] temp = new byte[128];
Array.Copy(transmitData, offset, temp, 0, transmitData.Length - offset >= 128 ? 128 : transmitData.Length - offset);
offset += 128;
//DisplayData(temp);
// Sending 128 bytes of data
port.Write(temp, 0, 128);
if (mode == Sym.NAK)
{
// Calculating and sending checksum
PortWriteByte(Checksum(temp));
}
else if (mode == Sym.C)
{
ShiftRegister register = new ShiftRegister(temp, true);
ushort crcOut = register.CalcCRC_16();
PortWriteByte((byte)(crcOut >> 8));
PortWriteByte((byte)crcOut);
}
// Wait for accept from the receiver
Sym result = WaitForAny(10);
if (result == Sym.NAK)
{
// If cheksum was incorrect - transmit packet once again
Console.WriteLine("Bad checksum!");
offset -= 128;
}
else if (result != Sym.ACK)
{
throw new InvalidOperationException();
}
}
private static Sym ReceivePacket(int timeoutSeconds, Sym protocolMode)
{
port.ReadTimeout = timeoutSeconds * 1000;
byte byteBuffer = 0;
byte[] dataBuffer = new byte[128];
byteBuffer = (byte)port.ReadByte();
//First time (for seq == 1) it shouldn't check for SOH, as the initialization has already read the SOH byte to check if data is coming
if (!first)
{
if (byteBuffer == (byte)Sym.SOH || byteBuffer == (byte)Sym.C)
{
byteBuffer = (byte)port.ReadByte(); // Here the seq number should be read
Console.WriteLine("Seq: " + byteBuffer);
}
else if (byteBuffer == (byte)Sym.EOT)
{
Console.WriteLine("Received EOT, cleaning up...");
return(Sym.EOT);
}
else if (byteBuffer == (byte)Sym.CAN)
{
throw new Exception("File transfer cancelled");
}
}
else
{
first = false;
}
// This isn't the best way to do this, but it works so whatever.
if (byteBuffer == seq)
{
// seq number received succesfully
byteBuffer = (byte)port.ReadByte(); // Here the cmpl seq should be read
if (byteBuffer == 255 - (255 & seq))
{
// cmpl seq received succesfully
// Increase seq
seq++;
if (seq == 0)
{
seq = 1; //Never let seq be 0, or the whole thing will fall apart
}
// Reading 128 bytes of data
for (int i = 0; i < 128; i++)
{
dataBuffer[i] = (byte)port.ReadByte();
}
Console.WriteLine("Received data:");
DisplayData(dataBuffer);
// Verifying checksum
// Warning! Here should be the switch for the checksum/CRC transmission
if (protocolMode == Sym.NAK)
{
byteBuffer = (byte)port.ReadByte();
if (byteBuffer != Checksum(dataBuffer))
{
//Handle wrong checksum
return(Sym.NAK);
}
else
{
//Handle succesful checksum
//Copy all bytes from buffer to receivedData
foreach (byte elem in dataBuffer)
{
receivedData.Enqueue(elem);
}
return(Sym.ACK);
}
}
else if (protocolMode == Sym.C)
{
byte[] dataCrc = new byte[130];
dataBuffer.CopyTo(dataCrc, 0);
dataCrc[128] = (byte)port.ReadByte();
dataCrc[129] = (byte)port.ReadByte();
ShiftRegister register = new ShiftRegister(dataCrc, false);
if (register.CalcCRC_16() == 0)
{
// Crc ok, proceed
foreach (byte elem in dataBuffer)
{
receivedData.Enqueue(elem);
}
return(Sym.ACK);
}
else
{
// Bad crc, repeat process
Console.WriteLine("Bad crc received, requesting retry.");
return(Sym.NAK);
}
}
}
else
{
throw new Exception("Bad complement of seq received!");
}
}
else
{
throw new Exception("Bad symbol or seq number!");
}
throw new InvalidOperationException("Reached unwanted area of ReceivePacket function!");
}
