使用定时器从 USB 读取

Question

我是使用 USB 的新手，正在尝试弄清楚如何运行后台计时器，然后当它触发时，从 USB 设备读取数据。以下是我用来启动计时器的方法以及计时器到期时触发的方法：

void myTimer_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
{
    //ReadUSB();
}

private void wndwMain_ContentRendered(object sender, EventArgs e)
{
    USBInit();
    if (deviceFound)
    {
        System.Timers.Timer myTimer = new System.Timers.Timer(1000);
        myTimer.Elapsed += new System.Timers.ElapsedEventHandler(myTimer_Elapsed);
        myTimer.Start();
    }
}

现在我想调用 ReadUSB()，但我抛出了 EntryPointNotFound 异常。我正在使用 Jan Axelson 的 USB 完整版中的 USB 代码。我知道延迟对于 USB 来说太长了，我只是将其放在那里用于测试目的，并且在验证一切正常后会减少延迟。

ReadUSB() 中的异常：

private void ReadUSB()
    {
        IntPtr eventObject = IntPtr.Zero;
        NativeOverlapped HidOverlapped = new NativeOverlapped();
        Byte[] inputReportBuffer = null;
        Int32 numberOfBytesRead = 0;
        Int32 result = 0;
        Boolean success = false;
        IntPtr unManagedBuffer = IntPtr.Zero;
        IntPtr unManagedOverlapped = IntPtr.Zero;

        Array.Resize(ref inputReportBuffer, Capabilities.InputReportByteLength);

        eventObject = CreateEvent
            (IntPtr.Zero,
            false,
            false,
            String.Empty);

        HidOverlapped.OffsetLow = 0;
        HidOverlapped.OffsetHigh = 0;
        HidOverlapped.EventHandle = eventObject;

        unManagedBuffer = Marshal.AllocHGlobal(inputReportBuffer.Length);
        unManagedOverlapped = Marshal.AllocHGlobal(Marshal.SizeOf(HidOverlapped));
        Marshal.StructureToPtr(HidOverlapped, unManagedOverlapped, false);

        readHandle = CreateFile
            (devicePathName,
            GENERIC_READ,
            FILE_SHARE_READ | FILE_SHARE_WRITE,
            IntPtr.Zero,
            OPEN_EXISTING,
            FILE_FLAG_OVERLAPPED,
            0);

        success = ReadFile
            (readHandle,
            unManagedBuffer,
            inputReportBuffer.Length,
            ref numberOfBytesRead,
            unManagedOverlapped);

        // If ReadFile returned true, report is available. Otherwise, check for completion
        if (!success)
        {
            result = WaitForSingleObject
                (eventObject, 3000);

            switch (result)
            {
                case WAIT_OBJECT_0:
                    success = true;
                    GetOverlappedResult
                        (readHandle,
                        unManagedOverlapped,
                        ref numberOfBytesRead,
                        false);
                    break;
                case WAIT_TIMEOUT:
                    Cancello(readHandle);  <-- Exception thrown here.
                    break;
                default:
                    Cancello(readHandle);
                    break;
            }
        }

Answer 1

该方法称为 CancelIo（带有大写的 I），而不是 Cancello（带有小写的 l） ）。