Jan Axelson, USB Complete

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various system IDs, any filter drivers or coinstallers the device uses, and power

capabilities. For example, the Device Instance ID contains the device’s Vendor

ID (VID) and Product ID (PID). A driver can provide custom property pages

when needed.

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The system registry is a database that Windows maintains for storing critical

information about the hardware and software installed on a system. The regis-

try stores information about devices that have been installed, including devices

not currently attached. After enumerating a new device, Windows stores infor-

mation about the device in the registry. The registry obtains some of its infor-

mation from the bus drivers, which in turn obtain the information from the

devices. Other information is from the INF file that the operating system

selects when assigning a driver to a device.

You can view the registry’s contents using Windows’ regedit utility (Start > Run

> regedit). You can also use regedit to edit the registry’s contents, but making

Figure 9-3. Device Manager also has an option to view devices grouped by type,

or function.

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registry changes this way isn’t recommended and is seldom necessary. The Win-

dows SDK documents API functions that enable applications to read and write

to the registry. Device installation adds or changes device information in the

registry. A request to uninstall a device via the Device Manager or another

application also results in registry changes.

The system registry is so important that Windows maintains multiple backup

copies in case the current copy becomes unusable. Windows’ System Restore

utility can restore the registry to an earlier state.

The registry’s data has a tree structure. Each node on the tree is a registry key.

Each key can have entries with assigned values and subkeys that in turn may

have entries and subkeys. Information about the system’s hardware and installed

software is under the HKEY_LOCAL_MACHINE key. Information about

USB devices is under several subkeys: the hardware key, the class key, the driver

key, and the service key.

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The hardware key, also called the instance key or device key, stores information

about an instance of a specific device. Hardware keys are under the enumerator

(Enum) key:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Enum

Under the Enum key is a USB key. Each subkey of the USB key contains the

Vendor ID and Product ID of a USB device. Figure 9-4 shows the entry for a

device with a Vendor ID of 0925h and Product ID or 1234h. Under each of

these keys may be one or more hardware keys, with each hardware key identify-

ing an instance of the device. Table 9-1 lists some of the entries under the hard-

ware key.

A device without a USB serial number gets a new hardware key every time the

device attaches to a port the device hasn’t been attached to previously. If you

physically remove the device from the bus and attach a different device with

identical descriptors to the same port, the operating system doesn’t know the

difference and thus doesn’t create a new hardware key. Devices with USB serial

numbers have one hardware key per physical device without regard to what port

the device attaches to.

A USB device may also have one or more keys for additional enumerators such

as HID, USBPRINT, and USBSTOR. For example, a UPS back-up device

with a HID interface can have a key in the Enum\USB branch for the HidUsb

service and a key in the Enum\HID branch for the HidBatt service.

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Figure 9-4. A hardware key contains information about an instance of a device

with a specific Vendor ID and Product ID.

Table 9-1: These are some of the entries in a USB device’s hardware key.

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Class Name of the device’s setup class

INF file (from

devguid.h)

ClassGUID GUID of the device’s setup class

INF file (from

devguid.h)

DeviceDesc Device Description INF file, Models section,

device description entry

HardwareID ID string containing the device’s Vendor

ID and Product ID

Device descriptor

CompatibleIDs ID string(s) containing the device’s class

and (optional) subclass and protocol

Device and interface descriptors

Mfg Device manufacturer INF file, Manufacturer section,

manufacturer name entry

Driver Name of the device’s driver key System registry, under

CurrentControlSet\Control\Class

Location

Information

“USB Device” or iProduct string Bus driver or string descriptor

Service Name of the device’s Service key System registry under

HKLM\System\

CurrentControlSet\Services

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The class key stores information about a device setup class and the devices that

belong to it. The class keys are under this registry key:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Class

The name of a class key is the device setup GUID for the class and is the same

as the value stored in the hardware key for devices in the class, under Class-

GUID. Figure 9-5 shows the class key for the HID class. The class key contains

a friendly name for the setup class, the class name from the header file that

defines the GUID, and an index value that specifies the icon to use in the

Device Manager and other windows that display setup information. Applica-

tions can retrieve the index of the mini-icon for a class by calling Setup-

DiGetClassBitmapIndex. A vendor-specific class installer or co-installer can

provide a vendor-specific icon.

Optional entries in the class key can affect what users see on device installation.

If NoInstallClass is present and not equal to zero, users will never need to man-

ually install devices in the class. If SilentInstall is present and not equal to zero,

the PnP manager will install devices in the class without displaying dialog boxes

or requiring user interaction. If NoDisplayClass is present and not equal to

zero, the Device Manager doesn’t display the class’s devices.

UpperFilters and LowerFilters entries can specify upper filter and lower filter

drivers that apply to all devices in the class.

Figure 9-5. The class key for the HID class includes a friendly name for the class

and an index to an icon.

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Table 9-2: The driver key contains information about the driver assigned to a

device.

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DriverDate Date of the driver file INF file, Version section,

DriverVer directive

DriverDesc Driver description INF file

DriverVer Driver version INF file, Version section,

DriverVer directive

InfPath Name of INF file INF file name

InfSection Name of the driver’s DDInstall

section

INF file

InfSectionExt “Decorated” extension used in INF

file (.NT, etc.)

INF file

MatchingDeviceID The hardware or compatible ID used

to assign the driver

Device descriptor and INF file

ProviderName The provider of the driver INF file, Provider string

Figure 9-6. The driver keys under each class key have information about the

drivers assigned to instances of devices in the class.

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Under the class key, each device in a class has a driver key, also called a software

key. In the hardware key for a device instance, the Driver entry names a device

setup GUID that matches a class key and a device instance number that

matches a driver subkey under the class key. Figure 9-6 shows the key for a

generic HID-class device. Table 9-2 lists some of the entries for a driver key.

The driver key contains the name of the INF file that in turn names the device’s

driver files.

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A service key has information about a driver’s files, including where they are

and how to load them. Service keys are in this branch:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services

Service keys exist for each host controller type, hubs, classes such as storage

(USBSTOR) and printers (USBPRINT), and HID functions (HidBatt, Hid-

Serv, HidUsb). Figure 9-7 shows the Service key for HidUsb.

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A device-setup information file, or INF file, is a text file that contains informa-

tion about one or more devices in a device setup class. The devices can be from

Figure 9-7. The service key names a driver’s file.

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one or more companies. The file tells system Setup components what driver or

drivers to use and contains information to store in the registry. Windows

includes INF files for the drivers provided with the operating system. The files

are in the %windir%\inf folder. The operating system copies any new INF files

for user-added devices to this folder.

By default, the INF folder is hidden. If you don’t see it in Windows Explorer,

select Tools > Folder Options > View, then under Hidden Files, select Show hid-

den files and folders. Do not select Hide file extensions for known file types.

On first attachment, after retrieving descriptors from a USB device, Windows

looks for a match between the information in the descriptors and the informa-

tion in the system’s INF files.

The WDK has a detailed reference on INF files and many examples. Often you

can begin with an example and customize it as needed. Listing 9-1 shows an

INF file for a device that uses the WinUSB driver.

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The contents of an INF file follow these rules.

• The information is arranged in sections, with each section containing one

or more items. The section name is in square brackets [ ]. Some of the sec-

tions (Version, Manufacturer) are standard sections that every INF file con-

tains. Other sections have names defined in other sections. For example,

the CopyFiles directive defines a section that contains names of files for the

installation process to copy. The sections can be in any order, but the order

of the items within a section can be critical.

• A semicolon (;) indicates a comment.

• Text enclosed in percent symbols (%sampletext%) is a token that refers to a

string. For example, you might have the following item:

DisplayName = %WinUSB_SvcDesc%

with an item in the Strings section that defines the string:

WinUSB_SvcDesc="WinUSB Demo"

• Windows defines Dirid values that can refer to system paths. The value for

the Windows directory (typically \Windows) is 10. Other ways to represent

the Windows directory are the environment variables %windir% and %Sys-

temRoot%. The System directory (%windir%\system32) is 11. The Drivers

directory (%windir%\system32\drivers) is 12.

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[Version]

Signature = "$Windows NT$"

Class = USB

ClassGUID={36FC9E60-C465-11CF-8056-444553540000}

Provider = %ProviderName%

DriverVer=02/07/2008,1.0.0

;CatalogFile=MyCatFile.cat

; Manufacturer

[Manufacturer]

%ProviderName% = MyDevice_WinUSB,NTx86,NTamd64

[MyDevice_WinUSB.NTx86]

%USB\MyDevice.DeviceDesc% =USB_Install, USB\VID_0925&PID_1456

[MyDevice_WinUSB.NTamd64]

%USB\MyDevice.DeviceDesc% =USB_Install, USB\VID_0925&PID_1456

; Installation

[USB_Install]

Include=winusb.inf

Needs=WINUSB.NT

[USB_Install.Services]

Include=winusb.inf

AddService=WinUSB,0x00000002,WinUSB_ServiceInstall

[WinUSB_ServiceInstall]

DisplayName = %WinUSB_SvcDesc%

ServiceType = 1

StartType = 3

ErrorControl = 1

ServiceBinary = %12%\WinUSB.sys

[USB_Install.Wdf]

KmdfService=WINUSB, WinUsb_Install

UmdfServiceOrder=WINUSB

Listing 9-1: This INF file is for a device that uses the WinUSB driver. (Part 1 of 3).

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[WinUSB_Install]

KmdfLibraryVersion=1.7

[USB_Install.HW]

AddReg=Dev_AddReg

[Dev_AddReg]

HKR,,DeviceInterfaceGUIDs,0x10000,"{42CA71EC-CE1C-44c2-82DE-87D8D8FF6C1E}"

[USB_Install.CoInstallers]

AddReg=CoInstallers_AddReg

CopyFiles=CoInstallers_CopyFiles

[CoInstallers_AddReg]

HKR,,CoInstallers32,0x00010000,"WinUSBCoInstaller.dll","WUDFUpdate_01007.dll","WdfCoInstal

ler01007.dll,WdfCoInstaller"

[CoInstallers_CopyFiles]

WinUSBCoInstaller.dll

WdfCoInstaller01007.dll

WUDFUpdate_01007.dll

[DestinationDirs]

CoInstallers_CopyFiles=11

; Source Media

[SourceDisksNames.x86]

1 = %DISK_NAME%,,,\i386

[SourceDisksNames.amd64]

2 = %DISK_NAME%,,,\amd64

[SourceDisksFiles.x86]

WinUSBCoInstaller.dll=1

WdfCoInstaller01007.dll=1

WUDFUpdate_01007.dll=1

Listing 9-1: This INF file is for a device that uses the WinUSB driver. (Part 2 of 3).

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235

• Some section names can use extensions to specify which operating systems

and/or CPUs the item applies to. For example, NTx86 means the item

applies only to systems with x86-based CPUs under Windows XP or later:

[MyDevice_WinUSB.NTx86]

Other extensions are NTamd64 for 64-bit CPUs based on the x86 architecture

and NTia64 for Itanium-based CPUs. A section name with this type of exten-

sion is called a decorated section name.

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A device that uses the WinUSB driver can use Listing 9-1’s INF file with the

following edits to customize the file for a specific device.

Two Models sections ([MyDevice_WinUSB.NTx86] and

[MyDevice_WinUSB.NTamd64]) each contain a device hardware ID value. In

[SourceDisksFiles.amd64]

WinUSBCoInstaller.dll=2

WdfCoInstaller01007.dll=2

WUDFUpdate_01007.dll=2

; Copy Files

[_CopyFiles_sys]

winusb.sys

; Destination Directories

[DestinationDirs]

DefaultDestDir = 12 ; %SystemRoot%\system32\drivers

_CopyFiles_sys = 12

; Strings

[Strings]

ProviderName="Lakeview Research"

USB\MyDevice.DeviceDesc="WinUSB Demo"

WinUSB_SvcDesc="WinUSB Demo"

DISK_NAME="My Install Disk"

Listing 9-1: This INF file is for a device that uses the WinUSB driver. (Part 3 of 3).