public sealed class Rfm9XDevice
   {
      private SpiDevice rfm9XLoraModem;
      private GpioPin InterruptGpioPin = null;
      private const byte RegisterAddressReadMask = 0X7f;
      private const byte RegisterAddressWriteMask = 0x80;

      public Rfm9XDevice(int chipSelectPin, int resetPin, int interruptPin)
      {
         var settings = new SpiConnectionSettings()
         {
            ChipSelectType = SpiChipSelectType.Gpio,
            ChipSelectLine = chipSelectPin,
            Mode = SpiMode.Mode0,
            ClockFrequency = 500000,
            DataBitLength = 8,
            ChipSelectActiveState = false,
         };

         SpiController spiCntroller = SpiController.FromName(FEZ.SpiBus.Spi1);

         rfm9XLoraModem = spiCntroller.GetDevice(settings);

         // Factory reset pin configuration
         GpioController gpioController = GpioController.GetDefault();
         GpioPin resetGpioPin = gpioController.OpenPin(resetPin);
         resetGpioPin.SetDriveMode(GpioPinDriveMode.Output);
         resetGpioPin.Write(GpioPinValue.Low);
         Thread.Sleep(10);
         resetGpioPin.Write(GpioPinValue.High);
         Thread.Sleep(10);

         // Interrupt pin for RX message & TX done notification 
         InterruptGpioPin = gpioController.OpenPin(interruptPin);
         resetGpioPin.SetDriveMode(GpioPinDriveMode.Input);

         InterruptGpioPin.ValueChanged += InterruptGpioPin_ValueChanged;
      }

      private void InterruptGpioPin_ValueChanged(GpioPin sender, GpioPinValueChangedEventArgs e)
      {
         if (e.Edge != GpioPinEdge.RisingEdge)
         {
            return;
         }

         byte irqFlags = this.RegisterReadByte(0x12); // RegIrqFlags
         Debug.WriteLine($"RegIrqFlags 0X{irqFlags:x2}");
         if ((irqFlags & 0b01000000) == 0b01000000)  // RxDone 
         {
            Debug.WriteLine("Receive-Message");
            byte currentFifoAddress = this.RegisterReadByte(0x10); // RegFifiRxCurrent
            this.RegisterWriteByte(0x0d, currentFifoAddress); // RegFifoAddrPtr

            byte numberOfBytes = this.RegisterReadByte(0x13); // RegRxNbBytes

            // Get number of bytes in the message
            byte[] messageBytes = this.RegisterRead(0x00, numberOfBytes);

            string messageText = UTF8Encoding.UTF8.GetString(messageBytes);
            Debug.WriteLine($"Received {messageBytes.Length} byte message {messageText}");
         }

         this.RegisterWriteByte(0x12, 0xff);// RegIrqFlags
      }
...
   class Program
   {
      static void Main()
      {
         Rfm9XDevice rfm9XDevice = new Rfm9XDevice(FEZ.GpioPin.D10, FEZ.GpioPin.D9, FEZ.GpioPin.D2);

         // Put device into LoRa + Sleep mode
         rfm9XDevice.RegisterWriteByte(0x01, 0b10000000); // RegOpMode 

         // Set the frequency to 915MHz
         byte[] frequencyWriteBytes = { 0xE4, 0xC0, 0x00 }; // RegFrMsb, RegFrMid, RegFrLsb
         rfm9XDevice.RegisterWrite(0x06, frequencyWriteBytes);

         rfm9XDevice.RegisterWriteByte(0x0F, 0x0); // RegFifoRxBaseAddress 

         rfm9XDevice.RegisterWriteByte(0x40, 0b00000000); // RegDioMapping1 0b00000000 DI0 RxReady & TxReady

         rfm9XDevice.RegisterWriteByte(0x01, 0b10000101); // RegOpMode set LoRa & RxContinuous

         rfm9XDevice.RegisterDump();

         Debug.WriteLine("Receive-Wait");
         Thread.Sleep(Timeout.Infinite);
      }
   }

'C:\Users\BrynLewis\source\repos\RFM9X.TinyCLR\ReceiveInterrupt\bin\Debug\pe\..\ReceiveInterrupt.exe', Symbols loaded.
The thread '<No Name>' (0x2) has exited with code 0 (0x0).
Register dump
Register 0x00 - Value 0X88
Register 0x01 - Value 0X85
Register 0x02 - Value 0X1a
..
Register 0x41 - Value 0X00
Register 0x42 - Value 0X12
Receive-Wait
RegIrqFlags 0X50
Receive-Message
Received 15 byte message HeLoRa World! 0
RegIrqFlags 0X50
Receive-Message
Received 15 byte message HeLoRa World! 2
RegIrqFlags 0X50
Receive-Message
Received 15 byte message HeLoRa World! 4
RegIrqFlags 0X50
Receive-Message
Received 15 byte message HeLoRa World! 6
RegIrqFlags 0X50
Receive-Message
Received 15 byte message HeLoRa World! 8
RegIrqFlags 0X50
Receive-Message
Received 16 byte message HeLoRa World! 10
RegIrqFlags 0X50
Receive-Message
Received 16 byte message HeLoRa World! 12