Auto Seeking USB Com Port in Windows

After you read previous article, I might know how to operate a com port in Windows.

But that example requires programmer (or user, if you modified that example being able to support inputting command line) to set a com port number, it is not consummate. I will fill the flaw in here.

You need to check the device enumeration path zeroth. In here, I use CH340 (USB com port chip from China)

You need to set hSerial as invalid in the begining of that code:

hSerial = INVALID_HANDLE_VALUE;

And you should replace that as the code below:

 hSerial = CreateFile(&comPortName[0], GENERIC_READ|GENERIC_WRITE, 0, NULL,
                OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL );

as

 if(0 == strncmp(&comPortName[0], "\\\\.\\COM0", MAX_STR_LEN))
 {
  unsigned int i;

  COMMCONFIG comConfig;
  DWORD dwSize;
  dwSize = sizeof(comConfig);

  ZeroMemory(&comConfig, sizeof(COMMCONFIG));

  for(i = 1; i< 256; i++){
   TCHAR comName[16];

   sprintf(&comName[0], "COM%d", i);

   if(FALSE != GetDefaultCommConfig(&comName[0], &comConfig, &dwSize))
    printf("found %s\n", &comName[0]);
  }/*for */

 }

 if(0 == strncmp(&comPortName[0], "\\\\.\\COM0", MAX_STR_LEN))
 {
  DWORD dwGuids;
  GUID *pGuids;  

  HDEVINFO hDevInfo;
  SP_DEVICE_INTERFACE_DATA devInterfaceData;
  SP_DEVINFO_DATA devInfoData;
  unsigned int index;

  dwGuids = 0;

  isSuc = SetupDiClassGuidsFromName("Ports", NULL, 0, &dwGuids);

  pGuids = (GUID*)malloc(dwGuids*sizeof(GUID));
  ZeroMemory(pGuids, dwGuids*sizeof(GUID));
  isSuc = SetupDiClassGuidsFromName("Ports", pGuids, dwGuids, &dwGuids);

  hDevInfo = SetupDiGetClassDevs(pGuids, NULL, NULL,
  /*DIGCF_ALLCLASSES | DIGCF_PRESENT |*/ DIGCF_DEVICEINTERFACE);  

  index = 0;

  ZeroMemory(&devInfoData, sizeof(SP_DEVINFO_DATA));
  devInfoData.cbSize = sizeof(SP_DEVINFO_DATA);

        while(SetupDiEnumDeviceInfo(hDevInfo, index, &devInfoData))
  {   

   TCHAR szDeviceInstanceID[1024];            

   index++;

   isSuc = CM_Get_Device_ID(devInfoData.DevInst,
     &szDeviceInstanceID[0] , sizeof(szDeviceInstanceID), 0);

   //printf("%s\n", &szDeviceInstanceID[0]);

   if(0 == strncmp(&szDeviceInstanceID[0], "USB\\VID_1A86&PID_7523",
    strlen("USB\\VID_1A86&PID_7523")) )
   {

    DWORD requiredSize;
    GUID classGuid;

    SP_DEVICE_INTERFACE_DATA   devInterfaceData;
    SP_DEVICE_INTERFACE_DETAIL_DATA *pDevInterfaceDetailData;

    printf("&szDeviceInstanceID[0] = %s\n", &szDeviceInstanceID[0]);

    ZeroMemory(&devInterfaceData, sizeof(SP_DEVICE_INTERFACE_DATA)); 

    devInterfaceData.cbSize = sizeof(SP_DEVICE_INTERFACE_DATA);
    classGuid = devInfoData.ClassGuid;

    isSuc = SetupDiEnumDeviceInterfaces(hDevInfo, &devInfoData, pGuids,
     0, &devInterfaceData);    

    isSuc = SetupDiGetDeviceInterfaceDetail(hDevInfo,
     &devInterfaceData, NULL, NULL, &requiredSize, NULL);

    //printf ("%s\n", GetLastErrorMessage( GetLastError() ) );

    pDevInterfaceDetailData = (SP_INTERFACE_DEVICE_DETAIL_DATA*)malloc(requiredSize);       

    pDevInterfaceDetailData->cbSize = sizeof(SP_INTERFACE_DEVICE_DETAIL_DATA);

    isSuc = SetupDiGetDeviceInterfaceDetail( hDevInfo,
     &devInterfaceData, pDevInterfaceDetailData, requiredSize,
     &requiredSize, &devInfoData);

    printf("devInterfaceDetailData.DevicePath = %s\n",
     pDevInterfaceDetailData->DevicePath);

    hSerial = CreateFile(pDevInterfaceDetailData->DevicePath,
     GENERIC_READ|GENERIC_WRITE, 0, NULL, OPEN_EXISTING,
     FILE_ATTRIBUTE_NORMAL, NULL );

    free(pDevInterfaceDetailData); pDevInterfaceDetailData = NULL;

    if(INVALID_HANDLE_VALUE != hSerial)
     break;
   }
  }           

  free(pGuids); pGuids = NULL;
  SetupDiDestroyDeviceInfoList(hDevInfo);

  if(INVALID_HANDLE_VALUE == hSerial)
  {
   printf("auto seeking com number fail!!\n");
   return 0;
  }
 }
 else /*non auto seeking com port*/
 {
  hSerial = CreateFile(&comPortName[0], GENERIC_READ | GENERIC_WRITE,
   0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL );
 }/*if auto seeking com port*/

("\\\\.\\COM0" be  auto-seeking mode in here.)

You have to modify the USB\\VID_1A86&PID_7523 as your device‘s.

( If you use FTDI‘s FT232B  or FT232R, that should be

FTDIBUS\\VID_0403+PID_6001

)

That would support auto-seeking com-port.

Note the line :

        while(SetupDiEnumDeviceInfo(hDevInfo, index, &devInfoData))

You would find NOT ONLY one device as VID_1A86&PID_7523, even you have plugged only one CH340. If you print that seeking result (it is just the line : printf("&szDeviceInstanceID[0] = %s\n", &szDeviceInstanceID[0]);), you would watch the printing as:

&szDeviceInstanceID[0] = USB\VID_1A86&PID_7523\6&123E8975&0&1
devInterfaceDetailData.DevicePath = \\?\usb#vid_1a86&pid_7523#6&123e8975&0&1#{4d
36e978-e325-11ce-bfc1-08002be10318}
&szDeviceInstanceID[0] = USB\VID_1A86&PID_7523\6&123E8975&0&2
devInterfaceDetailData.DevicePath = \\?\usb#vid_1a86&pid_7523#6&123e8975&0&2#{4d
36e978-e325-11ce-bfc1-08002be10318}
&szDeviceInstanceID[0] = USB\VID_1A86&PID_7523\6&123E8975&0&3
devInterfaceDetailData.DevicePath = \\?\usb#vid_1a86&pid_7523#6&123e8975&0&3#{4d
36e978-e325-11ce-bfc1-08002be10318}
&szDeviceInstanceID[0] = USB\VID_1A86&PID_7523\6&123E8975&0&4
devInterfaceDetailData.DevicePath = \\?\usb#vid_1a86&pid_7523#6&123e8975&0&4#{4d
36e978-e325-11ce-bfc1-08002be10318}
&szDeviceInstanceID[0] = USB\VID_1A86&PID_7523\6&123E8975&0&5
devInterfaceDetailData.DevicePath = \\?\usb#vid_1a86&pid_7523#6&123e8975&0&5#{4d
36e978-e325-11ce-bfc1-08002be10318}
&szDeviceInstanceID[0] = USB\VID_1A86&PID_7523\7&107B0B49&0&2
devInterfaceDetailData.DevicePath = \\?\usb#vid_1a86&pid_7523#7&107b0b49&0&2#{4d
36e978-e325-11ce-bfc1-08002be10318}
&szDeviceInstanceID[0] = USB\VID_1A86&PID_7523\7&14F85601&0&1
devInterfaceDetailData.DevicePath = \\?\usb#vid_1a86&pid_7523#7&14f85601&0&1#{4d
36e978-e325-11ce-bfc1-08002be10318}

I do not know why Windows lists so much device path. AlI I could do, is to try opening each. you could find that the actual one‘s last 4 characters (like &0&4, &0&2..etc) would change with port number, that depends on which
USB socket you plug.