HowTo: Com port emulation with CDC and usbser.sys ! 

From Dieter:

The descriptors and .inf file below are for a barcode reader:

You need to handle certain CDC requests (at least as dummies): 
SET_LINE_CODING 
SEND_ENCAPSULATED_COMMAND 
SET_CONTROL_LINE_STATE 
SEND_BREAK 
GET_LINE_CODING 
GET_ENCAPSULATED_RESPONSE 


It is possible to use the usbser.sys with an .inf file you need to write. 
USBSER.SYS has some problems; I never got the PnP work properly and now we use a custom driver. 

Copied from USBView: 
Device Descriptor: 
bcdUSB: 0x0110 
bDeviceClass: 0x02 
bDeviceSubClass: 0x00 
bDeviceProtocol: 0x00 
bMaxPacketSize0: 0x20 (32) 
idVendor: REPLACE WITH YOUR VID 
idProduct: REPLACE WITH YOUR PID 
bcdDevice: 0x0000 
iManufacturer: 0x01 
0x0409: "HHP" 
iProduct: 0x02 
0x0409: "IT4600" 
iSerialNumber: 0x08 
0x0409: "XXXXXX" 
bNumConfigurations: 0x01 

ConnectionStatus: DeviceConnected 
Current Config Value: 0x01 
Device Bus Speed: Full 
Device Address: 0x03 
Open Pipes: 3 

Endpoint Descriptor: 
bEndpointAddress: 0x83 
Transfer Type: Interrupt 
wMaxPacketSize: 0x0020 (32) 
bInterval: 0x02 

Endpoint Descriptor: 
bEndpointAddress: 0x81 
Transfer Type: Bulk 
wMaxPacketSize: 0x0040 (64) 
bInterval: 0x00 

Endpoint Descriptor: 
bEndpointAddress: 0x02 
Transfer Type: Bulk 
wMaxPacketSize: 0x0040 (64) 
bInterval: 0x00 

Configuration Descriptor: 
wTotalLength: 0x003E 
bNumInterfaces: 0x02 
bConfigurationValue: 0x01 
iConfiguration: 0x03 
0x0409: "Default" 
bmAttributes: 0xA0 (Bus Powered Remote Wakeup) 
MaxPower: 0xBB (374 Ma) 

Interface Descriptor: 
bInterfaceNumber: 0x00 
bAlternateSetting: 0x00 
bNumEndpoints: 0x01 
bInterfaceClass: 0x02 
bInterfaceSubClass: 0x02 
bInterfaceProtocol: 0x01 
iInterface: 0x04 
0x0409: "CDC-ACM Comm" 

Unknown Descriptor: 
bDescriptorType: 0x24 
bLength: 0x05 
05 24 00 10 01 

Unknown Descriptor: 
bDescriptorType: 0x24 
bLength: 0x05 
05 24 01 03 01 

Unknown Descriptor: 
bDescriptorType: 0x24 
bLength: 0x04 
04 24 02 06 

Endpoint Descriptor: 
bEndpointAddress: 0x83 
Transfer Type: Interrupt 
wMaxPacketSize: 0x0020 (32) 
bInterval: 0x02 

Interface Descriptor: 
bInterfaceNumber: 0x01 
bAlternateSetting: 0x00 
bNumEndpoints: 0x02 
bInterfaceClass: 0x0A 
bInterfaceSubClass: 0x00 
bInterfaceProtocol: 0x00 
iInterface: 0x05 
0x0409: "CDC-ACM Data" 

Endpoint Descriptor: 
bEndpointAddress: 0x81 
Transfer Type: Bulk 
wMaxPacketSize: 0x0040 (64) 
bInterval: 0x00 

Endpoint Descriptor: 
bEndpointAddress: 0x02 
Transfer Type: Bulk 
wMaxPacketSize: 0x0040 (64) 
bInterval: 0x00 
--------------------------------------------------- 


And here is my .inf file (Win2000,XP): 

[Version] 
Signature="$Windows NT$" 
Class=Ports 
ClassGuid={4D36E978-E325-11CE-BFC1-08002BE10318} 

Provider=%HHP% 
LayoutFile=layout.inf 
DriverVer=10/15/1999,5.0.2153.1 

[Manufacturer] 
%HHP%=HHP 

[HHP] 
%HHP5600%=Reader, USB\VID_0536&PID_016A 
%HHP5800%=Reader, USB\VID_0536&PID_018A 

[Reader_Install.NTx86] 
;Windows2000 

[DestinationDirs] 
DefaultDestDir=12 
Reader.NT.Copy=12 

[Reader.NT] 
CopyFiles=Reader.NT.Copy 
AddReg=Reader.NT.AddReg 

[Reader.NT.Copy] 
usbser.sys 

[Reader.NT.AddReg] 
HKR,,DevLoader,,*ntkern 
HKR,,NTMPDriver,,usbser.sys 
HKR,,EnumPropPages32,,"MsPorts.dll,SerialPortPropPageProvider" 

[Reader.NT.Services] 
AddService = usbser, 0x00000002, Service_Inst 

[Service_Inst] 
DisplayName = %Serial.SvcDesc% 
ServiceType = 1 ; SERVICE_KERNEL_DRIVER 
StartType = 3 ; SERVICE_DEMAND_START 
ErrorControl = 1 ; SERVICE_ERROR_NORMAL 
ServiceBinary = %12%\usbser.sys 
LoadOrderGroup = Base 

[Strings] 
HHP = "Hand Held Products, Inc." 
HHP5600 = "IT5600 Barcode Reader" 
HHP5800 = "IT5800 Barcode Reader" 
Serial.SvcDesc = "USB Serial emulation driver" 

No warranties of any kind! 
As I already said, we now use a custom driver and the .inf is a left over from my experiments. 

Please read these chapters in the CDC spec.: 
3.3 Interface Definitions 
3.3.1 Communication Class Interface 
3.3.2 Data Class Interface 
3.4 Endpoint Requirements 
3.4.1 Communication Class Endpoint Requirements 
3.4.2 Data Class Endpoint Requirements 
3.6.2 Abstract Control Model 
3.6.2.1 Abstract Control Model Serial Emulation 
4. Class-Specific Codes for Communication Devices 
All sub chapters of 4 as a reference 
5. Descriptors (as a reference) 
5.1 Standard USB Descriptor Definitions 
5.1.1 Device Descriptor 
5.1.2 Configuration Descriptor 
5.1.3 Interface Descriptors 
5.1.4 Endpoint Descriptors 
5.2 Class-Specific Descriptors 
5.2.1 Class-Specific Device Descriptor 
5.2.2 Class-Specific Configuration Descriptor 
5.2.3 Functional Descriptors 
5.2.3.1 Header Functional Descriptor 
5.2.3.2 Call Management Functional Descriptor 
5.2.3.3 Abstract Control Management Functional Descriptor 
6. Communication Interface Class Messages 
6.1 Overview 
6.2 Management Element Requests 
6.2.12 SetLineCoding 
6.2.13 GetLineCoding 
6.2.14 SetControlLineState 
6.3 Notification Element Notifications 
6.3.5 SerialState 


Additional INF file tips from Greg C:

Delete the "LayoutFile=layout.inf" line which is for INF files provided with the operating system. 

Add a "CatalogFile=catalog.cat" line in the Version section. (Use a null file of that name on your install disk until you get a real cat file from Microsoft.) 

Use the ChkInf tool provided in the DDK.