UWP 中串行设备通信的问题

Question

I have a peculiar problem.

I am trying to communicate with a peripheral unit that requires serial communication in a UWP project. I am using Windows.Devices.SerialCommunication .

For purpose of demonstration, I made a new page that has two buttons, with two different click handlers. One for opening the port, and the other for sending messages to the peripheral.

One handler is:

    SerialDevice device;
    
    private async void Button_Click_1(object sender, RoutedEventArgs e)
    {
         string selector = SerialDevice.GetDeviceSelector("COM7");
         DeviceInformationCollection devices = await DeviceInformation.FindAllAsync(selector);
             if (devices.Any())
             {
                 DeviceInformation deviceInfo = devices.First();
                 device = await SerialDevice.FromIdAsync(deviceInfo.Id);
                 //*********************
                 device.BaudRate = 9600;
                 device.DataBits = 8;
                 device.Parity = SerialParity.None;
                 device.StopBits = SerialStopBitCount.One;
                 device.ReadTimeout = device.WriteTimeout = TimeSpan.FromMilliseconds(1000);
                 device.Handshake = SerialHandshake.None;
             }
             _dataReader = new DataReader(device.InputStream);
             _dataWriter = new DataWriter(device.OutputStream);
    }

Peripheral has a red light on it when I enable the power supply. When the line above //********* is executed, the light is switched off. The peripheral doesn't respond to any messages then. When I stop the program, the light switches back on.

I made a .NET Framework app that works perfectly. It is fully functional. I used System.IO.Ports there. I noticed something:

If I extract and run only this part of the code in .NET Framework app:

SerialPort comPort = new SerialPort();            
_ComPort.PortName = PortName;
_ComPort.BaudRate = BaudRate;
_ComPort.DataBits = 8;
_ComPort.Parity = Parity.None;
_ComPort.StopBits = StopBits.One;
_ComPort.DataReceived += new SerialDataReceivedEventHandler(_ComPort_DataReceived);
_ComPort.Open();

Nothing more.

And run the UWP app again, the port opens perfectly, the lamp is red, and the device responds to messages. I can switch off the device, and initialize it from the UWP app as many times as I want to. When I restart my computer, I can't initialize the device from the UWP app again, (until I run the said block of code from .NET Framework app).

If you want to know, the peripheral is Bill to Bill unit made by Suzo Happ.

I didn't make any mistakes regarding property initialization in UWP.

Answer 1

I think this is the same issue I'm having. I repost here a description of the cause and a possible solution:

The UWP SerialDevice class currently only allows you to set "ReadTimeout", which under the hood, sets the "ReadIntervalTimeout" of the actual serial device ( https://learn.microsoft.com/en-us/windows/desktop/api/winbase/ns-winbase-_commtimeouts ). There are two other timeout values which dramatically affect the read operations behavior: 1) ReadTotalTimeoutMultiplier and 2) ReadTotalTimeoutConstant.

The UWP SerialDevice class does not allow the user to set these two other read timeout values, and even worse, the UWP SerialDevice class does not set these two other timeout values to known values when the serial device is opened. This means that the two other timeout values will be whatever default value the serial driver uses, or worse still, whatever value some serial port application happened to set these two values to be when the other application was last executed.

The overall effect of this is that your UWP application's serial device read behavior is undefined and cannot reliably be used. For example, if these two other timeout values happen to be set one way, then a read operation may block forever waiting on the first byte of data to be read, but if the other timeout values happen to be set a different way, then the read operation may return immediately, with no data read at all. Currently, a UWP application cannot control this behavior, and the behavior will be different across different serial ports, and even perhaps different every time the UWP application is executed.

The UWP SerialDevice class either needs to

1)Allow the user to set these two other read timeout values (preferred), OR 2)Initialize these two other timeout values to known values when the serial device is opened.