Fix duplicate packet reception on Arduino MKR 1310

[mdias]

Without this change there is a chance that we receive duplicate packets

[morganrallen]

Have you thoroughly checked the rest of your code to ensure something else isn't causing the duplicate? I've never encountered a situation where the IRQ doesn't clear.
You can test this by reading back the IRQ reg and printing out that value but note this also might fix your problem as it might just be the delay of two writes that's fixing and issue somewhere else.

[mdias]

The program I have that showed this happening rather easily was basically broadcasting a counter variable every second and checking for received packets all the time.
I have 2 Arduino MKR 1310 running the same program and both of them showed like 10-20% of the packets received being received twice.

I don't have enough knowledge to investigate further why the IRQs are not clearing, but after searching online I came across this issue describing the same problem but on a different board, and this fix was suggested. After trying the same fix on my board I could confirm that there are no longer duplicated received packets.

I understand that this looks like a hack and the problem may come from somewhere else, so I understand if you don't want to merge it as is. But the patch as is should also only affect the MKR 1310 board which is already misbehaving (the duplicates) with the original code.

[morganrallen]

There's an easy experiment you can try. Replace the new writeRegister call with delay(100). Does this also solve the problem?

[morganrallen]

It would also be helpful to understand this issue better if you could share the code around the call to endPacket

[mdias]

Replacing writeRegister with delay(100) results in some packets not being received at all, and some others are still duplicated.

My sample application is doing this when sending a packet:

void SendString(const char* str)
{
  digitalWrite(LED_BUILTIN, HIGH);

  LoRa.beginPacket();
  LoRa.print(str);
  LoRa.endPacket();

  digitalWrite(LED_BUILTIN, LOW);
}
...
static void sendData()
{
  char buf[16] = {0};
  if (secondsTimer()) // trigger only once a second
  {
    sprintf(buf, "%i", counter);
    DbgPrint("sending: "); // print debug info with Serial.print()
    DbgPrintLn(buf);

    ++counter;

    SendString(buf);
  }
}

On the receptor end, I receive data like so:

bool ReceiveString(String& outString)
{
  int packetSize = LoRa.parsePacket();
  if (packetSize <= 0)
  {
    return false;
  }

  while (LoRa.available())
  {  
    outString += (char)LoRa.read();
  }

  return true;
}

[maaaaaaaaaaaaaaaaaaaaaaaaaaax]

I got the same error on an MKR WAN 1300. I am reading the IRQ flags before and after the call of parsePacket(). Whenever a packet gets duplicated, the IRQ flags were not cleared after the call to parsePacket() but stayed at 64 instead.

I was able to fix this by checking the content of the IRQ flag register after the return of the call to parsePacket() and clearing the register again if it is not 0 at that point. I only have to clear it once and it works immediately. If I don't clear it again, it never clears by itself, so another writing to it is necessary.