serial connection on UWP Headless app

Question

I want to create a headless app for a Raspberry Pi that involves reading data from a serial port.

The sample app from Microsoft works fine, except that it has a user interface.

When creating the headless app, I took all relevant parts over as follows:

var aqs = SerialDevice.GetDeviceSelector();

var dis = await DeviceInformation.FindAllAsync(aqs);

foreach (var t in dis)
{
    if (t.Id.Contains("FTDI"))
    {
        listOfDevices.Add(t);

    }

}

if (listOfDevices.Count == 1)
{
    DeviceInformation entry = listOfDevices[0];

    try
    {
        serialPort = await SerialDevice.FromIdAsync(entry.Id);
        serialPort.WriteTimeout = TimeSpan.FromMilliseconds(1000);
        serialPort.ReadTimeout = TimeSpan.FromMilliseconds(1000);
        serialPort.BaudRate = 9600;
        serialPort.Parity = SerialParity.None;
        serialPort.StopBits = SerialStopBitCount.One;
        serialPort.DataBits = 8;
        serialPort.Handshake = SerialHandshake.None;

        ...

There is one USB-FTDI-cable, where the ID contains "FTDI" as follows:

serialPort = await SerialDevice.FromIdAsync(entry.Id);

The program reaches this line before the instance of the program disappears and ignores my breakpoint.

Any ideas?

Answer 1

I use your code and add the following lines in Package.appxmanifest.

<DeviceCapability Name="serialcommunication">
  <Device Id="any">
    <Function Type="name:serialPort" />
  </Device>
</DeviceCapability>

It works for me.

Update:

Based on your project(that you sent to me), because your ListAvailablePorts() is an asynchronous operation, you need to use the GetDeferral method to get a background task deferral to keep the host process from being suspended or terminated before the asynchronous operation complete. You can edit your code like this:

    BackgroundTaskDeferral _deferral = null;
    public async void Run(IBackgroundTaskInstance taskInstance)
    {
        _deferral = taskInstance.GetDeferral();
        // 
        // TODO: Insert code to start one or more asynchronous methods 
        //
        try
        {
            //var u = new USART();
            //await u.Initialize(115200, SerialParity.None, SerialStopBitCount.One, 8);
            listOfDevices = new ObservableCollection<DeviceInformation>();
            ListAvailablePorts();
        }

        ...
    }

And call _deferral.Complete() when the asynchronous operation is finished.