Question

我有一个C程序，它打开COM端口的句柄，向它写入一些字节，读取一些字节，然后关闭句柄并退出。但是，当我连续运行10次这样的程序时，它开始需要很长时间才能完成GetCommState功能并陷入SetCommState功能。在C＃中使用简单的SerialPort对象也会发生同样的事情。

我能找到的唯一解决办法是将设备重新连接到端口。是否有一些更优雅的方法来摆脱这种冻结？它可能只是一些PC配置错误吗？

更新

我重写了代码，使其使用DeviceIoControl代替SetCommState。但是，这里的问题完全相同。

device = 
    CreateFileW(
        L"\\\\.\\COM3", GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, 
        FILE_FLAG_OVERLAPPED, NULL);

static int SetBaudRate (HANDLE device) {
    int error = 0;
    int success = 0;
    OVERLAPPED overlapped = {0};
    overlapped.hEvent = CreateEvent(NULL, TRUE, 0, NULL);
    if (overlapped.hEvent) {
        SERIAL_BAUD_RATE baudRate = {0};
        baudRate.BaudRate = SERIAL_BAUD_115200;
        error = 
            DeviceIoControl(
                device, IOCTL_SERIAL_SET_BAUD_RATE, &baudRate, 
                sizeof(SERIAL_BAUD_RATE), NULL, 0, NULL, &overlapped);
        if (error || (!error && GetLastError() == ERROR_IO_PENDING)) {
            DWORD bytes = 0;
            if (GetOverlappedResult(device, &overlapped, &bytes, TRUE)) {
                success = 1;
            }
        }
    }
    CloseHandle(overlapped.hEvent);
    return success;
}

第一个问题：DeviceIoControl没有立即返回（虽然是异步调用）并且挂起大约两分钟。第二个问题：在这两分钟后失败，错误代码为121（ERR_SEM_TIMEOUT：“信号量超时时间已过期。”）。

使用过的驱动程序是标准的Windows驱动程序usbser.sys
有关为什么函数调用不会立即返回的任何想法？如果没有，如何为该功能设置更短的超时？
关于函数失败原因的任何想法？

更新2

样本C＃代码也会冻结（如上面的C程序）：

using System;
using System.IO.Ports;

sealed class Program {
    static void Main (string[] args) {
        int i = 0;
        while (true) {
            Console.WriteLine(++i);
            SerialPort p = 
                new SerialPort("com3", 115200, Parity.None, 8, StopBits.One);
            p.DtrEnable = true;
            p.RtsEnable = true;
            p.ParityReplace = 0;
            p.WriteTimeout = 10000;
            p.ReadTimeout = 3000;
            try {
                p.Open();
                Console.WriteLine("Success!");
            } catch (Exception e) {
                Console.WriteLine(e.GetType().Name + ": " + e.Message);
            }
            p.Close();
            Console.ReadLine();
        }
    }
}

示例输出如下：

1 (device not yet connected)
IOException: The port 'com3' does not exist.

2 (device connected but not yet in windows device manager)
IOException: The port 'com3' does not exist.

3
IOException: The port 'com3' does not exist.

4 (device connected and recognized)
Success!

5
Success!

[...] (with about one second between each enter press)

15
Success!

16 (device still connected and recognized - nothing touched! after two minutes of freeze, semaphore timeout exactly as in the C version)
IOException: The semaphore timeout period has expired.


17 (device disconnected during the two minutes of freeze. it then returns instantly)
IOException: A device attached to the system is not functioning.


18 (device still disconnected - note that the exception is a different one than the one in the beginning although it's the same case: device not connected)
IOException: The specified port does not exist.

19
IOException: The port 'com3' does not exist.

Answer 1

这是我的c ++类的一个工作部分，用于处理串口通信的变化，以适应C和您的需求。如果它不起作用，那么它可能是你的虚拟端口驱动程序错误

 DCB SerialPortSettings;
 HANDLE SerialPort;

int OpenPort(WCHAR* PortName,int BaudRate)
{

    SerialPort = CreateFileW(PortName,
        GENERIC_READ|GENERIC_WRITE,
        0,
        NULL,
        OPEN_EXISTING,
        FILE_FLAG_OVERLAPPED,
        NULL);

    if(SerialPort==INVALID_HANDLE_VALUE)
        return -2;

    RtlZeroMemory(&SerialPortSettings,sizeof(DCB));
    SerialPortSettings.DCBlength = sizeof(DCB);
    if(!GetCommState(SerialPort,&SerialPortSettings))
    {
        CloseHandle(SerialPort);
        return -3;
    }

    //8n1 RS485
    SerialPortSettings.BaudRate = BaudRate;
    SerialPortSettings.ByteSize = 8;
    SerialPortSettings.Parity = NOPARITY;
    SerialPortSettings.StopBits = ONESTOPBIT;
    SerialPortSettings.fRtsControl = RTS_CONTROL_TOGGLE;

    if(!SetCommState(SerialPort,&SerialPortSettings))
    {
        CloseHandle(SerialPort);
        return -4;
    }


    return 0;

}

编辑：尝试从http://www.ftdichip.com/Drivers/VCP.htm下载驱动程序，因为您所描述的问题很可能是驱动程序或设备问题。为Etan工作：）

使用usbser.sys冻结SerialPort.Open / DeviceIoControl / GetcommState

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