【发布时间】：2018-06-23 20:24:21
【问题描述】：
希望这里的人能够帮助我。我正在创建一个 c# UWP 应用程序以在 Raspberry Pi2 / Windows IOT 核心上运行。我需要从 2 个串行设备（由外部按钮/PLC 触发）读取输入以计算一些值。我能够一次读取其中一个设备，但到目前为止，我无法获得两者的价值。我基于我的序列代码示例，我试图从主页调用它。不管到目前为止我做了什么改变，第一个设备返回一个值，而第二个没有（串行处理程序中的等待任务立即返回 null，而不是等待一个值通过串行端口来）。
编辑：在进行了一些额外的故障排除后，我发现了以下问题 - 当我尝试停止调试时，Visual Studio 冻结（无法进行 UI 交互，但调试监控仍在更新），阻止这种情况的唯一方法是拔下将我的笔记本电脑（以及串行到 USB 电缆）的底座，此时 VS 再次正常运行。此外，我似乎在串行端口上的 while(true) 循环的第二次迭代中收到错误“请求的资源正在使用中。（来自 HRESULT 的异常：0x800700AA）”不起作用。
调用串口的代码是：
private async Task listenForDeviceInput()
{
string weight;
string area;
//var areaTask = cognosCamera.Listen();
//var weightTask = weighTable.Listen();
Task <string> areaTask = cognosCamera.Listen();
Task <string> weightTask = weighTable.Listen();
await Task.WhenAll(areaTask, weightTask);
weight = await weightTask;
area = await areaTask;
weight = weight.TrimEnds("\r");
area = area.TrimEnds("\r");
AddNewHide(weight, area);
saveHide();
listenForDeviceInput(); //removed the await here to see what happens
}
串行处理在这里：
// Copyright (c) Microsoft. All rights reserved.
using System;
using System.Collections.ObjectModel;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.Devices.Enumeration;
using Windows.Devices.SerialCommunication;
using Windows.Storage.Streams;
using System.Threading;
using System.Threading.Tasks;
namespace SerialDeviceHandler
{
public sealed partial class SerialPort
{
/// <summary>
/// Private variables
/// </summary>
private SerialDevice serialPort = null;
DataWriter dataWriteObject = null;
DataReader dataReaderObject = null;
private ObservableCollection<DeviceInformation> listOfDevices;
private CancellationTokenSource ReadCancellationTokenSource;
/// <summary>
/// ListAvailablePorts
/// - Use SerialDevice.GetDeviceSelector to enumerate all serial devices
/// - Attaches the DeviceInformation to the ListBox source so that DeviceIds are displayed
/// </summary>
/// <summary>
/// comPortInput_Click: Action to take when 'Connect' button is clicked
/// - Get the selected device index and use Id to create the SerialDevice object
/// - Configure default settings for the serial port
/// - Create the ReadCancellationTokenSource token
/// - Start listening on the serial port input
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
public async Task OpenSerialPort(string entry)
{
try
{
serialPort = await SerialDevice.FromIdAsync(entry);
if (serialPort == null) return;
// Configure serial settings
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;
// Create cancellation token object to close I/O operations when closing the device
ReadCancellationTokenSource = new CancellationTokenSource();
//Listen();
}
catch (Exception ex)
{
//status.Text = ex.Message;
//comPortInput.IsEnabled = true;
//sendTextButton.IsEnabled = false;
}
}
/// <summary>
/// WriteAsync: Task that asynchronously writes data from the input text box 'sendText' to the OutputStream
/// </summary>
/// <returns></returns>
/// <summary>
/// - Create a DataReader object
/// - Create an async task to read from the SerialDevice InputStream
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
public async Task<String> Listen()
{
string result;
try
{
if (serialPort != null)
{
dataReaderObject = new DataReader(serialPort.InputStream);
// keep reading the serial input
while (true)
{
result = await ReadAsync(ReadCancellationTokenSource.Token);
if(result != "Nothing" || result == null)
{
return result;
}
}
}
return "Failed";
}
catch (TaskCanceledException tce)
{
//status.Text = "Reading task was cancelled, closing device and cleaning up";
CloseDevice();
return "Task Cancelled";
}
catch (Exception ex)
{
//status.Text = ex.Message;
return "Task Errored";
}
finally
{
// Cleanup once complete
if (dataReaderObject != null)
{
dataReaderObject.DetachStream();
dataReaderObject = null;
}
}
}
/// <summary>
/// ReadAsync: Task that waits on data and reads asynchronously from the serial device InputStream
/// </summary>
/// <param name="cancellationToken"></param>
/// <returns></returns>
private async Task<string> ReadAsync(CancellationToken cancellationToken)
{
Task<UInt32> loadAsyncTask;
uint ReadBufferLength = 1024;
// If task cancellation was requested, comply
cancellationToken.ThrowIfCancellationRequested();
// Set InputStreamOptions to complete the asynchronous read operation when one or more bytes is available
dataReaderObject.InputStreamOptions = InputStreamOptions.Partial;
using (var childCancellationTokenSource = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken))
{
// Create a task object to wait for data on the serialPort.InputStream
loadAsyncTask = dataReaderObject.LoadAsync(ReadBufferLength).AsTask(childCancellationTokenSource.Token);
// Launch the task and wait
UInt32 bytesRead = await loadAsyncTask;
if (bytesRead > 0)
{
return dataReaderObject.ReadString(bytesRead);
//status.Text = "bytes read successfully!";
}
return "Nothing";
}
}
/// <summary>
/// CancelReadTask:
/// - Uses the ReadCancellationTokenSource to cancel read operations
/// </summary>
public void CancelReadTask()
{
if (ReadCancellationTokenSource != null)
{
if (!ReadCancellationTokenSource.IsCancellationRequested)
{
ReadCancellationTokenSource.Cancel();
}
}
}
/// <summary>
/// CloseDevice:
/// - Disposes SerialDevice object
/// - Clears the enumerated device Id list
/// </summary>
private void CloseDevice()
{
if (serialPort != null)
{
serialPort.Dispose();
}
serialPort = null;
//comPortInput.IsEnabled = true;
//sendTextButton.IsEnabled = false;
//rcvdText.Text = "";
listOfDevices.Clear();
}
/// <summary>
/// closeDevice_Click: Action to take when 'Disconnect and Refresh List' is clicked on
/// - Cancel all read operations
/// - Close and dispose the SerialDevice object
/// - Enumerate connected devices
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void closeDevice_Click(object sender, RoutedEventArgs e)
{
try
{
//status.Text = "";
CancelReadTask();
CloseDevice();
//ListAvailablePorts();
}
catch (Exception ex)
{
//status.Text = ex.Message;
}
}
}
据我所知，这 2 个串行端口对象似乎是正确创建的（基于这样一个事实，即如果我注释掉另一个的初始化，我可以从每个对象中获取一个值）。我将 2 个串行对象初始化为：
private async System.Threading.Tasks.Task InitializeSerialDevicesAsync()
{
weighTable = new SerialPort();
cognosCamera = new SerialPort();
await weighTable.OpenSerialPort(scaleComPort);
await cognosCamera.OpenSerialPort(cameraComPort);
}
我知道我可能只是在做一些愚蠢的事情，但任何帮助将不胜感激。在这一点上，我只是想让它在普通 PC 上运行，然后我必须开始处理 Pi 上的驱动程序问题等。
【问题讨论】：
标签： c# uwp raspberry-pi windows-10-iot-core