Question

I have a GSM modem connected via USB. The modem creates 2 serial ports. The first is automatically attached to the modem, the second shows in Device Manager as ‘HUAWEI Mobile Connect – 3G PC UI Interface (COM6)’

The second port is used to get vital information from the modem, such as signal quality; to send and receive text messages; and a whole host of other functions.

I am writing an application that will wrap up some of the features provided by the second port. What I need is a sure fire method of identifying which COM port is the spare one. Iterating the ports and checking a response to ‘ATE0’ is not sufficient. The modem’s port is usually the lower numbered one, and when a dial up connection is not active, it will respond to ‘ATE0’ the same as the second port.

What I was thinking of doing is iterating the ports and checking their friendly name, as it shows in Device Manager. That way I can link the port in my application to the port labelled ‘HUAWEI Mobile Connect – 3G PC UI Interface (COM6)’ in Device Manager. I’ve just not found any information yet that will allow me to get that name programmatically.

Answer 1

The information posted by Will Dean was most helpful. This is the code that eventually worked for me. Everything in the PInvoke class was taken verbatim from http://www.pinvoke.net . I did have to change a data type here or there to make it work (like when using an enum instead of a uint) but it should be easy to figure out.

internal static string GetComPortByDescription(string Description) {     string Result = string.Empty;     Guid guid = PInvoke.GUID_DEVCLASS_PORTS;     uint nDevice = 0;     uint nBytes = 300;     byte[] retval = new byte[nBytes];     uint RequiredSize = 0;     uint PropertyRegDataType = 0;      PInvoke.SP_DEVINFO_DATA devInfoData = new PInvoke.SP_DEVINFO_DATA();     devInfoData.cbSize = Marshal.SizeOf(typeof(PInvoke.SP_DEVINFO_DATA));      IntPtr hDeviceInfo = PInvoke.SetupDiGetClassDevs(         ref guid,          null,          IntPtr.Zero,          PInvoke.DIGCF.DIGCF_PRESENT);      while (PInvoke.SetupDiEnumDeviceInfo(hDeviceInfo, nDevice++, ref devInfoData))     {         if (PInvoke.SetupDiGetDeviceRegistryProperty(                 hDeviceInfo,                  ref devInfoData,                  PInvoke.SPDRP.SPDRP_FRIENDLYNAME,                 out PropertyRegDataType,                  retval,                  nBytes,                  out RequiredSize))         {             if (System.Text.Encoding.Unicode.GetString(retval).Substring(0, Description.Length).ToLower() ==                 Description.ToLower())             {                 string tmpstring = System.Text.Encoding.Unicode.GetString(retval);                 Result = tmpstring.Substring(tmpstring.IndexOf('COM'),tmpstring.IndexOf(')') - tmpstring.IndexOf('COM'));             } // if retval == description         } // if (PInvoke.SetupDiGetDeviceRegistryProperty( ... SPDRP_FRIENDLYNAME ...     } // while (PInvoke.SetupDiEnumDeviceInfo(hDeviceInfo, nDevice++, ref devInfoData))      PInvoke.SetupDiDestroyDeviceInfoList(hDeviceInfo);     return Result; } 

I think the line Result = tmpstring.Substring(tmpstring.IndexOf('COM'),tmpstring.IndexOf(')') - tmpstring.IndexOf('COM')); is a little clumsy, suggestions on how to clean it up would be appreciated.

Thanks for your help with this matter Will, without you, I’d still be searching google.