Serial communication is slow

[system]

I've found the solution. The writeByte function of jSSC is highly inefficient in this case. If i premade the 49 byte buffer in Java then pass it at once to jSSC i get a very big speed boost.

    byte[] sendBuffer = new byte[49];
    sendBuffer[0] = 'd';

    for (byte i = 0; i < 48; i++) {
      sendBuffer[i + 1] = i;
    }
    port.writeBytes(sendBuffer);

With baud rate 345600 it gives me now ~240 packets/sec (~12KB/sec).