Indicating the end of a data stream

Projects Interfacing w/ Software on the Computer
1

Hello,
I have this piece of wiring code that reads a data stream from lora wireless network and passes it through USB Interface:

void onLoRaReceive(int packetSize) {
  if (packetSize == 0) {
    indicateError();
    return;          // if there's no packet, return
  }

  byte[packetSize] buffer=[];
  
  while (LoRa.available()) {
    site_t recievedData=LoRa.readBytes(buffer,packetSize);
    Serial.write(buffer,recievedData);
  }
}

void indicateError(){
  digitalWrite(ERROR_LED_INDICATOR,HIGH);
  sleep(1000);
  digitalWrite(ERROR_LED_INDICATOR,LOW);
}

My question is on how to indicate the end of the stream/packet to the usb interface? My idea is to use either EOF or '\0' character but I fear is that some LoRa Packet may have Rogue EOF or '\0' characters that may indicate prematurely the End of the serial stream.

I have also seen the arduino uno - How to indicate an End of a stream on USB - Arduino Stack Exchange without any answer.

2

The second and third examples in Serial Input Basics may give you some ideas.

...R

3

Is your data text or binary? If the former, see Robin's reply.

If it's binary, you need to design a complete protocol that will contain a start marker, a length indication, the data and a crc so you can check that the packet is indeed a packet; a timeout might also be useful.

Regarding the start marker, it depends on the type of data that you want to transfer; if it's e.g. values obtained with analogRead(), 0xFFFF can be used. If it's status of switches, you can transfer 7 switches in a byte and the 8th bit can indicate start of packet; in which case the other seven bits contain either the status (start marker 0) or can contain the length of the message (start marker 1). Your creativity is the limit :wink:

What is at the receiving end of the USB?

4

to overcome the problem of frame flags in a data stream you can use bit or byte stuffing