PacketIO

A PlatformIO library for framing packets sent or received over an arduino Stream, such as Serial.

The framing methods are exposed through the PacketPrint and PacketStream interfaces.

• PacketPrint - extends Print:
  • bool end() - end a packet, returning whether it was sucessfull
  • void abort() - try as best as possible to start a new packet
• PacketStream - extends Stream:
  • read(), peek() - return PacketStream::EOP (-2) if the packet is complete (without touching the underlying stream), otherwise behaves as normal
  • next() - stop reading from this packet, and move on

Framing Protocols

Implemented so far

• COBS
• SLIPS
• COBS-R
• Length-prefixed

Examples

Writing

// pick a protocol here - everything below doesn't need to change
COBSPrint cobs_out(Serial);

PacketPrint& out = cobs_out;

out.print("Hello ");
out.print("World");
out.end(); // mark the end of a packet

out.print("Goodbye ");
if(something_went_horribly_wrong) {
	out.abort(); // terminate this packet early and try to mark what was sent as bad
}
else {
	out.print("World");
	out.end();
}

Reading

// pick a protocol here - everything below doesn't need to change
COBSStream cobs_in(Serial);

PacketStream& in = cobs_in;

while(true) {
	char message[10];
	size_t n = 0;

	while(true) {
		// read until we get something
		int c = in.read();
		if(c == in::EOF) continue;

		// detect End Of Packet
		if(c == in::EOP) break;

		// save anything else
		message[n++] = c;
	}

	Serial.print("Got: ");
	Serial.write(message, n);
	Serial.println();

	// start reading the next message
	in.next();
}

Future work

Provide an interface to nanopb, that converts Print into pb_ostream_s and Stream into pb_istream_s, to allow protobufs to be framed.