RFM9X.NetMF on Github

After a month of posts the source code of V0.9 of my RFM9X/SX127X library is on GitHub. I included all of the source for my test harness and proof of concept(PoC) applications so other people can follow along with “my learning experience”.

I need to trial with some more hardware, frequency bands, variety of clients, initialisation configurations and backport the last round of fixes from my .Net library.

The simplest possible application .NetMF using the new library

/---------------------------------------------------------------------------------
// Copyright (c) August 2018, devMobile Software
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
//---------------------------------------------------------------------------------
namespace devMobile.IoT.NetMF.Rfm9X.Client
{
   using System;
   using System.Text;
   using System.Threading;
   using devMobile.IoT.NetMF.ISM;
   using Microsoft.SPOT;
   using SecretLabs.NETMF.Hardware.Netduino;

   public class Program
   {
      public static void Main()
      {
         Rfm9XDevice rfm9XDevice = new Rfm9XDevice(Pins.GPIO_PIN_D10, Pins.GPIO_PIN_D9, Pins.GPIO_PIN_D2);
         byte MessageCount = Byte.MinValue;

         rfm9XDevice.Initialise( Rfm9XDevice.RegOpModeMode.ReceiveContinuous, 915000000, paBoost: true, rxPayloadCrcOn: true);
         rfm9XDevice.OnDataReceived += rfm9XDevice_OnDataReceived;
         rfm9XDevice.OnTransmit += rfm9XDevice_OnTransmit;

         while (true)
         {
            string messageText = "Hello NetMF LoRa! " + MessageCount.ToString();
            MessageCount += 1;
            byte[] messageBytes = UTF8Encoding.UTF8.GetBytes(messageText);
            Debug.Print("Sending " + messageBytes.Length + " bytes message " + messageText);
            rfm9XDevice.SendMessage(messageBytes);

            Thread.Sleep(10000);
         }
      }

      static void rfm9XDevice_OnTransmit()
      {
         Debug.Print("Transmit-Done");
      }

      static void rfm9XDevice_OnDataReceived(byte[] data)
      {
         try
         {
            string messageText = new string(UTF8Encoding.UTF8.GetChars(data));

            Debug.Print("Received " + data.Length.ToString() + " byte message " + messageText);
         }
         catch (Exception ex)
         {
            Debug.Print(ex.Message);
         }
      }
   }
}

// Dirty hack for Rosyln 
namespace System.Diagnostics
{
   public enum DebuggerBrowsableState
   {
      Never = 0,
      Collapsed = 2,
      RootHidden = 3
   }
}

I need to do more testing (especially of the initialisation options) and will add basic device addressing soon so my field gateway will only see messages which it is interested in.

Rfm9xLoRaDevice LNA gain revisited

While fixing up the Signal to Noise Ratio(SNR) and Received Signal Strength Indication(RSSI) in a previous post I noted the Low Noise Amplifier(LNA) had High Frequency(LF) and Low Frequency settings.

First step was to update the initialise method parameter list (the parameter list is huge but for most values the defaults are fine)

		public void Initialise(RegOpModeMode modeAfterInitialise, // RegOpMode
			double frequency = FrequencyDefault, // RegFrMsb, RegFrMid, RegFrLsb
			bool rxDoneignoreIfCrcMissing = true, bool rxDoneignoreIfCrcInvalid = true,
			bool paBoost = false, byte maxPower = RegPAConfigMaxPowerDefault, byte outputPower = RegPAConfigOutputPowerDefault, // RegPaConfig
			bool ocpOn = true, byte ocpTrim = RegOcpOcpTrimDefault, // RegOcp
			RegLnaLnaGain lnaGain = LnaGainDefault, bool lnaBoostLF = false, bool lnaBoostHf = false, // RegLna
			RegModemConfigBandwidth bandwidth = RegModemConfigBandwidthDefault, RegModemConfigCodingRate codingRate = RegModemConfigCodingRateDefault, RegModemConfigImplicitHeaderModeOn implicitHeaderModeOn = RegModemConfigImplicitHeaderModeOnDefault, //RegModemConfig1
			RegModemConfig2SpreadingFactor spreadingFactor = RegModemConfig2SpreadingFactorDefault, bool txContinuousMode = false, bool rxPayloadCrcOn = false,
			ushort symbolTimeout = SymbolTimeoutDefault,
			ushort preambleLength = PreambleLengthDefault,
			byte payloadLength = PayloadLengthDefault,
			byte payloadMaxLength = PayloadMaxLengthDefault,
			byte freqHoppingPeriod = FreqHoppingPeriodDefault,
			bool lowDataRateOptimize = false, bool agcAutoOn = false,
			byte ppmCorrection = ppmCorrectionDefault,
			RegDetectOptimizeDectionOptimize detectionOptimize = RegDetectOptimizeDectionOptimizeDefault,
			bool invertIQ = false,
			RegisterDetectionThreshold detectionThreshold = RegisterDetectionThresholdDefault,
			byte syncWord = RegSyncWordDefault)
		{

which became

public void Initialise(RegOpModeMode modeAfterInitialise, // RegOpMode
	double frequency = FrequencyDefault, // RegFrMsb, RegFrMid, RegFrLsb
	bool rxDoneignoreIfCrcMissing = true, bool rxDoneignoreIfCrcInvalid = true,
	bool paBoost = false, byte maxPower = RegPAConfigMaxPowerDefault, byte outputPower = RegPAConfigOutputPowerDefault, // RegPaConfig
	bool ocpOn = true, byte ocpTrim = RegOcpOcpTrimDefault, // RegOcp
	RegLnaLnaGain lnaGain = LnaGainDefault, bool lnaBoost = false, // RegLna
	RegModemConfigBandwidth bandwidth = RegModemConfigBandwidthDefault, RegModemConfigCodingRate codingRate = RegModemConfigCodingRateDefault, RegModemConfigImplicitHeaderModeOn implicitHeaderModeOn = RegModemConfigImplicitHeaderModeOnDefault, //RegModemConfig1
	RegModemConfig2SpreadingFactor spreadingFactor = RegModemConfig2SpreadingFactorDefault, bool txContinuousMode = false, bool rxPayloadCrcOn = false,
	ushort symbolTimeout = SymbolTimeoutDefault,
	ushort preambleLength = PreambleLengthDefault,
	byte payloadLength = PayloadLengthDefault,
	byte payloadMaxLength = PayloadMaxLengthDefault,
	byte freqHoppingPeriod = FreqHoppingPeriodDefault,
	bool lowDataRateOptimize = false, bool agcAutoOn = false,
	byte ppmCorrection = ppmCorrectionDefault,
	RegDetectOptimizeDectionOptimize detectionOptimize = RegDetectOptimizeDectionOptimizeDefault,
	bool invertIQ = false,
	RegisterDetectionThreshold detectionThreshold = RegisterDetectionThresholdDefault,
	byte syncWord = RegSyncWordDefault)
{

Then in the code for configuring the RegLna the frequency band is checked

		// Set RegLna if any of the settings not defaults
			if ((lnaGain != LnaGainDefault) || (lnaBoost != false))
			{
				byte regLnaValue = (byte)lnaGain;
				if (lnaBoost)
				{
					if (Frequency > RFMidBandThreshold)
					{
						regLnaValue |= RegLnaLnaBoostHfOn;
					}
					else
					{
						regLnaValue |= RegLnaLnaBoostLfOn;
					}
				}
				RegisterManager.WriteByte((byte)Registers.RegLna, regLnaValue);
			}

The HF & LF differences where not obviously handled in Arduino-LoRa library and the Semtech LoRaMac node GitHub repository wasn’t so helpful this time.

Not so confident with these changes need to test with my 434MHz devices

Rfm9xLoRaDevice SNR and RSSI revisited

The magic numbers for the high frequency(HF) vs. low frequency(LF) adjustment bugged me

int rssi = this.RegisterManager.ReadByte((byte)Registers.RegRssiValue);
if (Frequency < 868E6)
	rssi = -164 + rssi; // LF output port
else
	rssi = -157 + rssi; // HF output port

int packetRssi = this.RegisterManager.ReadByte((byte)Registers.RegPktRssiValue);
if (Frequency < 868E6)
	packetRssi = -164 + rssi; // LF output port
else
	packetRssi = -157 + rssi; // HF output port

After some searching I ended up at the Semetch LoRaMac node github repository. In that code they had a number of constants which looked like a better approach.

if( SX1276.Settings.Channel > RF_MID_BAND_THRESH )
{
   rssi = RSSI_OFFSET_HF + SX1276Read( REG_LR_RSSIVALUE );
}
else
{
   rssi = RSSI_OFFSET_LF + SX1276Read( REG_LR_RSSIVALUE );
}

I also fixed a couple of bugs I noticed with the maths and the code now looks like this

int rssi = this.RegisterManager.ReadByte((byte)Registers.RegRssiValue);
if (Frequency > RFMidBandThreshold)
   rssi = RssiAdjustmentHF + rssi;
else
   rssi = RssiAdjustmentLF + rssi;

int packetRssi = this.RegisterManager.ReadByte((byte)Registers.RegPktRssiValue);
if (Frequency > RFMidBandThreshold)
   packetRssi = RssiAdjustmentHF + packetRssi;
else
   packetRssi = RssiAdjustmentLF + packetRssi;

This has also got me thing about how RegLna – LnaBoostLf/LnaBoostHf should be handled as well.

Rfm9xLoRaDevice SNR and RSSI

The signal to noise Ratio (SNR) and Received Signal Strength Indication(RSSI) for inbound messages required reading values from three registers

  • RegPktSnrValue
  • RegPktRssiValue
  • RegRssiValue

I had to modify the EventArgs returned to the customer

public class OnDataReceivedEventArgs : EventArgs
{
	public float PacketSnr { get; set; }
	public int PacketRssi { get; set; }
	public int Rssi { get; set; }
	public byte[] Data { get; set; }
}

I was inspired by the RSSI adjustment approach used in the Arduino-LoRa library

// Get the RSSI HF vs. LF port adjustment section 5.5.5 RSSI and SNR in LoRa Mode
float packetSnr = this.RegisterManager.ReadByte((byte)Registers.RegPktSnrValue) * 0.25f;

int rssi = this.RegisterManager.ReadByte((byte)Registers.RegRssiValue);
if (Frequency < 868E6)
	rssi = -164 - rssi; // LF output port
else
	rssi = -157 + rssi; // HF output port

int packetRssi = this.RegisterManager.ReadByte((byte)Registers.RegPktRssiValue);
if (Frequency < 868E6)
	packetRssi = -164 - rssi; // LF output port
else
	packetRssi = -157 - rssi; // HF output port

OnDataReceivedEventArgs receiveArgs = new OnDataReceivedEventArgs
{
	PacketSnr = packetSnr,
	Rssi = rssi,
	PacketRssi = packetRssi,
	Data = messageBytes
};

The values displayed in the Rfm9xLoRaDeviceClient application looked reasonable, but will need further checking

RFM9X.IoTCore on Github

After a month of posts the source code of V0.9 of my RFM9X/SX127X library is on GitHub. I included all of the source for my test harness and proof of concept(PoC) applications so other people can follow along with “my learning experience”.

I started wanting a library to for a LoRa telemetry field gateway and ended up writing one (which is usually not a good idea). My use case was a device that was configured, then run for long periods of time, was not battery powered, and if settings were changed could be restarted. I need to trial with some more hardware, frequency bands, variety of clients, initialisation configurations and backport the last round of fixes to my .NetMF library.

I am also looking at writing an RFM69 library using a pair of shields (434MHz & 915MHz)  from seegel-systeme.

The simplest possible application using the new library (a fair bit of the code is to support the different supported shields)

//---------------------------------------------------------------------------------
// Copyright (c) August 2018, devMobile Software
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
//---------------------------------------------------------------------------------
namespace devMobile.IoT.Rfm9x.LoRaDeviceClient
{
	using System;
	using System.Diagnostics;
	using System.Text;
	using System.Threading.Tasks;

	using devMobile.IoT.Rfm9x;
	using Windows.ApplicationModel.Background;

	public sealed class StartupTask : IBackgroundTask
    {
		private byte NessageCount = Byte.MaxValue;
#if DRAGINO
		private const byte ChipSelectLine = 25;
		private const byte ResetLine = 17;
		private const byte InterruptLine = 4;
		private Rfm9XDevice rfm9XDevice = new Rfm9XDevice(ChipSelectPin.CS0, ChipSelectLine, ResetLine, InterruptLine);
#endif
#if M2M
		private const byte ChipSelectLine = 25;
		private const byte ResetLine = 17;
		private const byte InterruptLine = 4;
		private Rfm9XDevice rfm9XDevice = new Rfm9XDevice(ChipSelectPin.CS0, ChipSelectLine, ResetLine, InterruptLine);
#endif
#if ELECROW
		private const byte ResetLine = 22;
		private const byte InterruptLine = 25;
		private Rfm9XDevice rfm9XDevice = new Rfm9XDevice(ChipSelectPin.CS1, ResetLine, InterruptLine);
#endif
#if ELECTRONIC_TRICKS
		private const byte ResetLine = 22;
		private const byte InterruptLine = 25;
		private Rfm9XDevice rfm9XDevice = new Rfm9XDevice(ChipSelectPin.CS0, 22, 25);
#endif

		public void Run(IBackgroundTaskInstance taskInstance)
		{
			rfm9XDevice.Initialise(Rfm9XDevice.RegOpModeMode.ReceiveContinuous, 915000000.0, paBoost: true);

#if DEBUG
			rfm9XDevice.RegisterDump();
#endif
			rfm9XDevice.OnReceive += Rfm9XDevice_OnReceive;
			rfm9XDevice.OnTransmit += Rfm9XDevice_OnTransmit;

			Task.Delay(10000).Wait();

			while (true)
			{
				string messageText = string.Format("Hello W10 IoT Core LoRa! {0}", NessageCount);
				NessageCount -= 1;

				byte[] messageBytes = UTF8Encoding.UTF8.GetBytes(messageText);
				Debug.WriteLine("{0:HH:mm:ss}-TX {1} byte message {2}", DateTime.Now, messageBytes.Length, messageText);
				this.rfm9XDevice.Send(messageBytes);

				Task.Delay(10000).Wait();
			}
		}

		private void Rfm9XDevice_OnReceive(object sender, Rfm9XDevice.OnDataReceivedEventArgs e)
		{
			try
			{
				string messageText = UTF8Encoding.UTF8.GetString(e.Data);

				Debug.WriteLine("{0:HH:mm:ss}-RX {1} byte message {2}", DateTime.Now, e.Data.Length, messageText);
			}
			catch (Exception ex)
			{
				Debug.WriteLine(ex.Message);
			}
		}

		private void Rfm9XDevice_OnTransmit(object sender, Rfm9XDevice.OnDataTransmitedEventArgs e)
		{
			Debug.WriteLine("{0:HH:mm:ss}-TX Done", DateTime.Now);
		}
	}
}

I have a shield from uputronics on order which should arrive from the UK in roughly a week. This shield has two RFM9X devices onboard (In my case 434MHz & 915MHz) so it will be interesting to see how my library copes with two instances of the stack running together.

I need to do more testing (especially of the initialisation options) and will add basic device addressing soon so my field gateway will only see messages which it is interested in.

M2M Low power LoRaWan Node Model B1284

Along with the M2M LoRaWan Gateway Shield for Raspberry Pi I also purchased a Low power LoRaWan Node Model B1284. After configuring Arduino IDE then downloading the necessary board configuration files (link to instructions was provided) I could down upload my Arduino-Lora based test application .

LoRaWanNodeV1_0.jpg
Initially the program failed with “LoRa init failed. Check your connections.” so I went back and checked the board configuration details and noticed that the chip select line was different.

const int csPin = 14;          // LoRa radio chip select
const int resetPin = 9;       // LoRa radio reset
const int irqPin = 2;         // change for your board; must be a hardware interrupt pin

byte msgCount = 0;            // count of outgoing messages
int interval = 2000;          // interval between sends
long lastSendTime = 0;        // time of last packet send

void setup() {
  Serial.begin(9600);                   // initialize serial
  while (!Serial);

  Serial.println("LoRa Duplex - Set sync word");

  // override the default CS, reset, and IRQ pins (optional)
  LoRa.setPins(csPin, resetPin, irqPin);// set CS, reset, IRQ pin

  if (!LoRa.begin(915E6)) {             // initialize ratio at 915 MHz
    Serial.println("LoRa init failed. Check your connections.");
    while (true);                       // if failed, do nothing
  }

  LoRa.enableCrc();

  LoRa.setSyncWord(0x12);           // ranges from 0-0xFF, default 0x34, see API docs

  LoRa.dumpRegisters(Serial);
  Serial.println("LoRa init succeeded.");
}

void loop() {
  if (millis() - lastSendTime > interval) {
    String message = "11 Hello Arduino LoRa! ";   // send a message
    message += msgCount;
    sendMessage(message);
    Serial.println("Sending " + message);
    lastSendTime = millis();            // timestamp the message
    //interval = random(2000) + 1000;    // 2-3 seconds
    interval = 1000;
  }

  // parse for a packet, and call onReceive with the result:
  onReceive(LoRa.parsePacket());
}

void sendMessage(String outgoing) {
  LoRa.beginPacket();                   // start packet
  LoRa.print(outgoing);                 // add payload
  LoRa.endPacket();                     // finish packet and send it
  msgCount++;                           // increment message ID
}

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

  // read packet header bytes:
  String incoming = "";

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

  Serial.println("Message: " + incoming);
  Serial.println("RSSI: " + String(LoRa.packetRssi()));
  Serial.println("Snr: " + String(LoRa.packetSnr()));
  Serial.println();
}

When I uploaded my application I found the device had significantly more memory available

Sketch uses 8456 bytes (27%) of program storage space. Maximum is 30720 bytes.
vs..
Sketch uses 10424 bytes (8%) of program storage space. Maximum is 130048 bytes.

With the size of the LMIC stack this additional extra headroom could be quite useful. For most my LoRa applications (which tend to be a couple of simple sensors) I think the Low Power LoRaWan Node Model A328 should be sufficient.

M2M LoRaWan Node Model A328

Along with the M2M LoRaWan Gateway Shield for Raspberry Pi I also purchased a Low power LoRaWan Node Model A328. After setting the Board in Arduino IDE to Arduino pro mini 8Mhz 3V the device fired up and worked first time.

LoRaWanNodeV3_5
The device is intended for LoRaWan applications so the samples provided (including a link to application template generator) were not that applicable for my LoRa project so I used the Arduino LoRa library.

const int csPin = 10;          // LoRa radio chip select
const int resetPin = 9;       // LoRa radio reset
const int irqPin = 2;         // change for your board; must be a hardware interrupt pin

byte msgCount = 0;            // count of outgoing messages
int interval = 2000;          // interval between sends
long lastSendTime = 0;        // time of last packet send

void setup() {
  Serial.begin(9600);                   // initialize serial
  while (!Serial);

  Serial.println("LoRa Duplex - Set sync word");

  // override the default CS, reset, and IRQ pins (optional)
  LoRa.setPins(csPin, resetPin, irqPin);// set CS, reset, IRQ pin

  if (!LoRa.begin(915E6)) {             // initialize ratio at 915 MHz
    Serial.println("LoRa init failed. Check your connections.");
    while (true);                       // if failed, do nothing
  }

  LoRa.enableCrc();

  LoRa.setSyncWord(0x12);           // ranges from 0-0xFF, default 0x34, see API docs

  LoRa.dumpRegisters(Serial);
  Serial.println("LoRa init succeeded.");
}

void loop() {
  if (millis() - lastSendTime > interval) {
    String message = "0 Hello Arduino LoRa! ";   // send a message
    message += msgCount;
    sendMessage(message);
    Serial.println("Sending " + message);
    lastSendTime = millis();            // timestamp the message
    //interval = random(2000) + 1000;    // 2-3 seconds
    interval = 1000;
  }

  // parse for a packet, and call onReceive with the result:
  onReceive(LoRa.parsePacket());
}

void sendMessage(String outgoing) {
  LoRa.beginPacket();                   // start packet
  LoRa.print(outgoing);                 // add payload
  LoRa.endPacket();                     // finish packet and send it
  msgCount++;                           // increment message ID
}

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

  // read packet header bytes:
  String incoming = "";

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

  Serial.println("Message: " + incoming);
  Serial.println("RSSI: " + String(LoRa.packetRssi()));
  Serial.println("Snr: " + String(LoRa.packetSnr()));
  Serial.println();
}

I did find the “grove” connectors weren’t compatible with any of my sensors, but the vendor does include a number of cables DIY connection.

GroveConnectorIssue20180822

Next I’ll use power conservation modes and see how long I can get a set of AAA batteries to last. The device looks like a good option (esp. with solar power for devices with higher power consumption sensors) for some of the SmartAg projects my students are building.

In my Windows 10 IoT Core test application I could see the enableCrc() method was working according to the RegHopChannel CrcOnPayload flag.

For real deployments of the field gateway I think packets which have no CRC or a corrupted one will be dropped.