要与HID设备通信,我使用kernel32中的一些功能。代码是从Microchip MLA定制HID设备项目中借用的。它使用阻止方法。
我发现我可以使这些方法异步。这是我尝试异步写入的内容:
//...
internal const uint FILE_FLAG_OVERLAPPED = 0x40000000;
//...
[DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
private static extern bool ReadFile(
SafeFileHandle hFile,
IntPtr lpBuffer,
uint nNumberOfBytesToRead,
ref uint lpNumberOfBytesRead,
Overlapped lpOverlapped); // Formerly: IntPtr lpOverlapped);
//...
WriteHandleToUSBDevice = CreateFile(DevicePath, GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE, IntPtr.Zero,
OPEN_EXISTING, FILE_FLAG_OVERLAPPED, IntPtr.Zero); // Formerly: 0 instead of FILE_FLAG_OVERLAPPED
//...
Overlapped OL = new Overlapped();
WriteFile(WriteHandleToUSBDevice, OUTBuffer, 65, ref BytesWritten, OL); // Formerly: IntPtr.Zero instead of OL
//Some code to run while write operation is in progress asynchronously...
while (OL.AsyncResult == null) ; // Wait until write is completed; waits forever.
您可以在Microchip MLA自定义HID设备项目中找到完整的代码。
OL.AsyncResult
保持为空,尽管写入成功完成;我敢肯定,因为设备可以正确接收数据和响应。我的代码有什么问题?
答案 0 :(得分:0)
感谢Gserg的评论,我找到了比使用kernel32 C ++样式函数更好的解决方案:
SafeFileHandle HandleToUSBDevice = CreateFile(DevicePath, GENERIC_READ | GENERIC_WRITE,
FILE_SHARE_READ | FILE_SHARE_WRITE, IntPtr.Zero, OPEN_EXISTING, FILE_FLAG_OVERLAPPED,
IntPtr.Zero);
FileStream HID = new FileStream(HandleToUSBDevice, FileAccess.ReadWrite, (int)(PacketSize + 1), true);
Task WriteTask = Task.Factory.StartNew(() => HID.Write(OUTBuffer, 0, 65));
//Some Code
if (!WriteTask.Wait(2500)) throw new TimeoutException("Failed to send data within 2.5s timeout.");
如果您的.Net框架目标大于4.5,则可以使用async/await
和WriteAsync
。
我可以使用ReadFile
代替HID.Write
,但是关闭句柄会更困难。同样,使用托管C#方法比导入和使用非托管C ++函数要好。
编辑: 我还为BeginRead添加了代码:
IAsyncResult result = HID.BeginRead(INBuffer, 0, 65, null, null);
while (FavoriteCondition)
{
MethodWhichShouldBeCalledRepeatedly();
if (result.IsCompleted)
{
ProcessData(INBuffer);
}
}