Receive Interrupt

The HopeRF datasheet coverage of how the hardware interrupts should be configured (RegDioMapping1 & RegDioMapping2) was a bit confusing and some of the other values where wrong e.g. RegVersion returned 0x12 rather than 0x11.

I figured that getting interrupts working was a good choice to do next while the code was still relatively small. From the LMIC LoRaWAN stack implementations I have looked at the mapping of digital pins in hardware and software appeared critical.

I modified my test application and set what I though was the correct RegDioMapping1 for DIO0 but the application didn’t work the way I expected. After some searching then tinkering I went back and checked my approach against the Semtech SX1276 datasheet. I found the byte ordering was backwards to what I assumed (The two DIO0 bits were bits 7&6 of RegDioMapping1 not bits 1&0)

I also added an extra parameter to the constructor to pass in the interrupt pin number, replaced the message sending code, with an infinite sleep, then wired up the interrupt handler. In this proof of concept the interrupt handler just displays the received message which is a bit fugly.

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// Copyright (c) August 2018, devMobile Software
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// Licensed under the Apache License, Version 2.0 (the "License");
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namespace devMobile.IoT.Rfm9x.ReceiveInterrupt
{
	using System;
	using System.Diagnostics;
	using System.Text;
	using System.Runtime.InteropServices.WindowsRuntime;
	using System.Threading.Tasks;
	using Windows.ApplicationModel.Background;
	using Windows.Devices.Spi;
	using Windows.Devices.Gpio;

	public sealed class Rfm9XDevice
	{
		private SpiDevice Rfm9XLoraModem = null;
		private GpioPin ChipSelectGpioPin = null;
		private GpioPin InterruptGpioPin = null;
		private const byte RegisterAddressReadMask = 0X7f;
		private const byte RegisterAddressWriteMask = 0x80;

		public Rfm9XDevice(byte chipSelectPin, byte resetPin, byte interruptPin)
		{
			SpiController spiController = SpiController.GetDefaultAsync().AsTask().GetAwaiter().GetResult();
			var settings = new SpiConnectionSettings(0)
			{
				ClockFrequency = 500000,
				Mode = SpiMode.Mode0,
			};

			// Chip select pin configuration
			GpioController gpioController = GpioController.GetDefault();
			ChipSelectGpioPin = gpioController.OpenPin(chipSelectPin);
			ChipSelectGpioPin.SetDriveMode(GpioPinDriveMode.Output);
			ChipSelectGpioPin.Write(GpioPinValue.High);

			// Reset pin configuration to do factory reset
			GpioPin resetGpioPin = gpioController.OpenPin(resetPin);
			resetGpioPin.SetDriveMode(GpioPinDriveMode.Output);
			resetGpioPin.Write(GpioPinValue.Low);
			Task.Delay(10);
			resetGpioPin.Write(GpioPinValue.High);
			Task.Delay(10);

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

			InterruptGpioPin.ValueChanged += InterruptGpioPin_ValueChanged;

			Rfm9XLoraModem = spiController.GetDevice(settings);
		}

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

			byte IrqFlags = this.RegisterReadByte(0x12); // RegIrqFlags
			Debug.WriteLine( string.Format("RegIrqFlags {0}", Convert.ToString(IrqFlags, 2).PadLeft(8, '0')));
			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

				// Allocate buffer for message
				byte[] messageBytes = new byte[numberOfBytes];

				for (int i = 0; i < numberOfBytes; i++)
				{
					messageBytes[i] = this.RegisterReadByte(0x00); // RegFifo
				}

				string messageText = UTF8Encoding.UTF8.GetString(messageBytes);
				Debug.WriteLine("Received {0} byte message {1}", messageBytes.Length, messageText);
			}

			this.RegisterWriteByte(0x12, 0xff);// RegIrqFlags
		}

		public Byte RegisterReadByte(byte address)
		{
			byte[] writeBuffer = new byte[] { address &= RegisterAddressReadMask };
			byte[] readBuffer = new byte[1];
			Debug.Assert(Rfm9XLoraModem != null);

			ChipSelectGpioPin.Write(GpioPinValue.Low);
			Rfm9XLoraModem.Write(writeBuffer);
			Rfm9XLoraModem.Read(readBuffer);
			ChipSelectGpioPin.Write(GpioPinValue.High);

			return readBuffer[0];
		}

		public ushort RegisterReadWord(byte address)
		{
			byte[] writeBuffer = new byte[] { address &= RegisterAddressReadMask };
			byte[] readBuffer = new byte[2];
			Debug.Assert(Rfm9XLoraModem != null);

			ChipSelectGpioPin.Write(GpioPinValue.Low);
			Rfm9XLoraModem.Write(writeBuffer);
			Rfm9XLoraModem.Read(readBuffer);
			ChipSelectGpioPin.Write(GpioPinValue.High);

			return (ushort)(readBuffer[1] + (readBuffer[0] << 8));
		}

		public byte[] RegisterRead(byte address, int length)
		{
			byte[] writeBuffer = new byte[] { address &= RegisterAddressReadMask };
			byte[] readBuffer = new byte[length];
			Debug.Assert(Rfm9XLoraModem != null);

			ChipSelectGpioPin.Write(GpioPinValue.Low);
			Rfm9XLoraModem.Write(writeBuffer);
			Rfm9XLoraModem.Read(readBuffer);
			ChipSelectGpioPin.Write(GpioPinValue.High);

			return readBuffer;
		}

		public void RegisterWriteByte(byte address, byte value)
		{
			byte[] writeBuffer = new byte[] { address |= RegisterAddressWriteMask, value };
			Debug.Assert(Rfm9XLoraModem != null);

			ChipSelectGpioPin.Write(GpioPinValue.Low);
			Rfm9XLoraModem.Write(writeBuffer);
			ChipSelectGpioPin.Write(GpioPinValue.High);
		}

		public void RegisterWriteWord(byte address, ushort value)
		{
			byte[] valueBytes = BitConverter.GetBytes(value);
			byte[] writeBuffer = new byte[] { address |= RegisterAddressWriteMask, valueBytes[0], valueBytes[1] };
			Debug.Assert(Rfm9XLoraModem != null);

			ChipSelectGpioPin.Write(GpioPinValue.Low);
			Rfm9XLoraModem.Write(writeBuffer);
			ChipSelectGpioPin.Write(GpioPinValue.High);
		}

		public void RegisterWrite(byte address, [ReadOnlyArray()] byte[] bytes)
		{
			byte[] writeBuffer = new byte[1 + bytes.Length];
			Debug.Assert(Rfm9XLoraModem != null);

			Array.Copy(bytes, 0, writeBuffer, 1, bytes.Length);
			writeBuffer[0] = address |= RegisterAddressWriteMask;

			ChipSelectGpioPin.Write(GpioPinValue.Low);
			Rfm9XLoraModem.Write(writeBuffer);
			ChipSelectGpioPin.Write(GpioPinValue.High);
		}

		public void RegisterDump()
		{
			Debug.WriteLine("Register dump");
			for (byte registerIndex = 0; registerIndex <= 0x42; registerIndex++)
			{
				byte registerValue = this.RegisterReadByte(registerIndex);

				Debug.WriteLine("Register 0x{0:x2} - Value 0X{1:x2} - Bits {2}", registerIndex, registerValue, Convert.ToString(registerValue, 2).PadLeft(8, '0'));
			}
		}
	}

	public sealed class StartupTask : IBackgroundTask
	{
		private const byte ChipSelectLine = 25;
		private const byte ResetLine = 17;
		private const byte InterruptLine = 4;
		private Rfm9XDevice rfm9XDevice = new Rfm9XDevice(ChipSelectLine, ResetLine, InterruptLine);

		public void Run(IBackgroundTaskInstance taskInstance)
		{
			// 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 DIO0 RxReady & TxReady

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

			rfm9XDevice.RegisterDump();

			Debug.WriteLine("Receive-Wait");
			Task.Delay(-1).Wait();
		}
	}
}

The output in the output debug window looked like this

RegIrqFlags 01010000
Receive-Message
Received 15 byte message HeLoRa World! 0
RegIrqFlags 01010000
Receive-Message
Received 15 byte message HeLoRa World! 2
RegIrqFlags 01010000
Receive-Message
Received 15 byte message HeLoRa World! 4
RegIrqFlags 01010000
Receive-Message
Received 15 byte message HeLoRa World! 6

Next step will be wiring up the transmit done interrupt.