Nasty OTAA connect
After getting basic connectivity for my IoT LoRa Node pHAT for Raspberry Pi test rig sorted I wanted to see if I could get the device connected to The Things Network(TTN) via the RAK7246G LPWAN Developer Gateway on my bookcase.
My Over the Air Activation (OTAA) implementation is very “nasty” I have assumed that there would be no timeouts or failures and I only send one BCD message “48656c6c6f204c6f526157414e” which is “hello LoRaWAN”.
The code just sequentially steps through the necessary configuration to join the TTN network with a suitable delay after each command is sent. I had some problems with re-opening the serial port if my application had previously failed with an uncaught exception. After some experimentation I added some code to ensure the port was closed when an exception occurred.
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// Copyright (c) September 2021, devMobile Software
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namespace devMobile.IoT.NetCore.Rak811.NetworkJoinOTAA
{
using System;
using System.Diagnostics;
using System.IO.Ports;
using System.Threading;
public class Program
{
private const string SerialPortId = "/dev/ttyS0";
private const string AppEui = "...";
private const string AppKey = "...";
private const byte MessagePort = 1;
private const string Payload = "A0EEE456D02AFF4AB8BAFD58101D2A2A"; // Hello LoRaWAN
public static void Main()
{
string response;
Debug.WriteLine("devMobile.IoT.NetCore.Rak811.NetworkJoinOTAA starting");
Debug.WriteLine(String.Join(",", SerialPort.GetPortNames()));
try
{
using (SerialPort serialPort = new SerialPort(SerialPortId))
{
// set parameters
serialPort.BaudRate = 9600;
serialPort.DataBits = 8;
serialPort.Parity = Parity.None;
serialPort.StopBits = StopBits.One;
serialPort.Handshake = Handshake.None;
serialPort.ReadTimeout = 5000;
serialPort.NewLine = "\r\n";
serialPort.Open();
// clear out the RX buffer
response = serialPort.ReadExisting();
Debug.WriteLine($"RX :{response.Trim()} bytes:{response.Length}");
Thread.Sleep(500);
// Set the Working mode to LoRaWAN
Console.WriteLine("Set Work mode");
serialPort.WriteLine("at+set_config=lora:work_mode:0");
Thread.Sleep(5000);
response = serialPort.ReadExisting();
response = response.Trim('\0');
Debug.WriteLine($"RX :{response.Trim()} bytes:{response.Length}");
// Set the Region to AS923
Console.WriteLine("Set Region");
serialPort.WriteLine("at+set_config=lora:region:AS923");
response = serialPort.ReadLine();
Debug.WriteLine($"RX :{response.Trim()} bytes:{response.Length}");
// Set the JoinMode
Console.WriteLine("Set Join mode");
serialPort.WriteLine("at+set_config=lora:join_mode:0");
response = serialPort.ReadLine();
Debug.WriteLine($"RX :{response.Trim()} bytes:{response.Length}");
// Set the appEUI
Console.WriteLine("Set App Eui");
serialPort.WriteLine($"at+set_config=lora:app_eui:{AppEui}");
response = serialPort.ReadLine();
Debug.WriteLine($"RX :{response.Trim()} bytes:{response.Length}");
// Set the appKey
Console.WriteLine("Set App Key");
serialPort.WriteLine($"at+set_config=lora:app_key:{AppKey}");
response = serialPort.ReadLine();
Debug.WriteLine($"RX :{response.Trim()} bytes:{response.Length}");
// Set the Confirm flag
Console.WriteLine("Set Confirm off");
serialPort.WriteLine("at+set_config=lora:confirm:0");
response = serialPort.ReadLine();
Debug.WriteLine($"RX :{response.Trim()} bytes:{response.Length}");
// Join the network
Console.WriteLine("Start Join");
serialPort.WriteLine("at+join");
Thread.Sleep(10000);
response = serialPort.ReadLine();
Debug.WriteLine($"RX :{response.Trim()} bytes:{response.Length}");
while (true)
{
Console.WriteLine("Sending");
serialPort.WriteLine($"at+send=lora:{MessagePort}:{Payload}");
Thread.Sleep(1000);
// The OK
Console.WriteLine("Send result");
response = serialPort.ReadLine();
Debug.WriteLine($"RX :{response.Trim()} bytes:{response.Length}");
// The Signal strength information etc.
Console.WriteLine("Network confirmation");
response = serialPort.ReadLine();
Debug.WriteLine($"RX :{response.Trim()} bytes:{response.Length}");
Thread.Sleep(20000);
}
}
}
catch (Exception ex)
{
Debug.WriteLine(ex.Message);
}
}
}
}
The code is not suitable for production but it confirmed my software and hardware configuration worked.
In the Visual Studio 2019 debug output I could see messages getting sent and then after a short delay they were visible in the TTN console.
The RAK811 doesn’t fully implement the AS923 specification but I have a work around detailed in another post.
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