How to Use WinUSB to Communicate with a USB Device

How to Use WinUSB to Communicate with a USB Device March 30, 2009 Abstract Independent hardware vendors (IHVs) who manufacture USB devices must often provide a way for applications to access the device’s features. Historically, this has meant using the Windows® Driver Model (WDM) to implement a function driver for the device and installing the driver in the device stack above system-supplied protocol drivers. The Windows Driver Foundation (WDF) is now the preferred model for USB drivers. It provides IHVs with three options for providing access to a USB device: • Implementing a user-mode driver by using the WDF user-mode driver framework (UMDF). • Implementing a kernel-mode driver by using the WDF kernel-mode driver framework (KMDF). • Installing WinUsb.sys as the device’s function driver and providing an application that accesses the device by using the WinUSB API. This white paper provides guidelines for when to use each option and includes a detailed walkthrough of how to install WinUsb.sys as a device’s function driver and use the WinUSB API to communicate with the device. This information applies for the following operating systems: Windows 7 Windows Server® 2008 Windows Vista® Windows XP References and resources discussed here are listed at the end of this paper. For the latest information, see: http://www.microsoft.com/whdc/connect/usb/winusb_howto.mspx Disclaimer: This is a preliminary document and may be changed substantially prior to final commercial release of the software described herein. The information contained in this document represents the current view of Microsoft Corporation on the issues discussed as of the date of publication. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information presented after the date of publication. This White Paper is for informational purposes only. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS DOCUMENT. Complying with all applicable copyright laws is the responsibility of the user. Without limiting the rights under copyright, no part of this document may be reproduced, stored in or introduced into a retrieval system, or transmitted in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise), or for any purpose, without the express written permission of Microsoft Corporation. Microsoft may have patents, patent applications, trademarks, copyrights, or other intellectual property rights covering subject matter in this document. Except as expressly provided in any written license agreement from Microsoft, the furnishing of this document does not give you any license to these patents, trademarks, copyrights, or other intellectual property. Unless otherwise noted, the example companies, organizations, products, domain names, e-mail addresses, logos, people, places and events depicted herein are fictitious, and no association with any real company, organization, product, domain name, email address, logo, person, place or event is intended or should be inferred. © 2009 Microsoft Corporation. All rights reserved. Microsoft, MSDN, Windows, Windows Server, and Windows Vista are either registered trademarks or trademarks of Microsoft Corporation in the United States and/or other countries. The names of actual companies and products mentioned herein may be the trademarks of their respective owners. Revision History Date Change March 30, 2009  Added additional information for communicating with endpoints. December 6, 2007  Added a section on DFU to the WinUSB FAQ.  Removed the note from Table 1 indicating that WinUSB does not support WinUSB selective suspend on Windows XP. August 30, 2007 Created Contents Introduction 4 Summary of WinUSB, UMDF, and KMDF Capabilities 5 Guidelines for Providing Access to USB Devices 6 Introduction to WinUSB 6 WinUSB FAQ 7 How to Install WinUsb.sys as a Function Driver 8 How to Use the WinUSB API 12 Obtain a Handle to the Device and Initialize WinUSB 12 Obtain the Device Path 13 Obtain a File Handle for the Device 15 Initialize WinUSB 15 Configure the Device 15 Communicate with Endpoints 17 Control Requests 17 WinUSB I/O Requests 19 WinUSB Write Requests 19 Default WinUSB Write Behavior 20 WinUSB Read Requests 20 Default WinUSB Read Behavior 20 Pipe Policies 21 WinUSB Power Management 23 Selective Suspend 23 Detecting Idle 23 Future Feature Considerations 23 Summary 24 Resources 24 Introduction Independent hardware vendors (IHVs) who manufacture USB devices must typically provide a way for applications to access the device’s features. Historically, this has meant using the Windows® Driver Model (WDM) to implement a function driver for the device and installing the driver in the device stack above system-supplied protocol drivers such as Usbhub.sys or Usbccgp.sys. The function driver exposes a device interface that applications use to obtain the device’s file handle. They can then use the handle to communicate with the driver by calling Windows API functions such as ReadFile and DeviceIoControl. Drivers are the most flexible way to provide access to a USB device and allow the device to be accessed by any application, including multiple concurrent applications. However, drivers require a significant development effort, and some devices are simple enough that they do not require the full support of a custom function driver. For example, devices such as machine controllers or data loggers are typically accessed only by a single application that was written specifically for the associated device. In these cases, WinUSB provides a simpler alternative to implementing a custom USB driver. WinUSB was developed concurrently with the Windows Driver Foundation (WDF) and is available for Windows XP and later versions of Windows. It includes a kernel-mode driver, WinUsb.sys, which is an integral part of WDF user-mode driver framework (UMDF) support for USB drivers. However, for USB devices that are accessed by only a single application, vendors can often install WinUsb.sys as their device’s function driver instead of implementing a custom driver. The application can then configure the device and access its endpoints by using the WinUSB API. For those USB devices that require the features of a custom function driver, the preferred approach is WDF. The WDF programming model and device driver interface (DDI) makes WDF USB drivers much easier to implement than equivalent WDM drivers. You can implement WDF USB drivers in either of the following ways: • Use the user-mode driver framework (UMDF) to implement user-mode USB drivers for most USB devices for Windows XP and later. • Use the kernel-mode driver framework (KMDF) to implement kernel-mode USB drivers for any USB device for Windows 2000 and later. This white paper describes how to choose the best way to provide applications with access to a USB device and answers some common questions about WinUSB. The bulk of the paper is a detailed walkthrough—including code samples—of how to install WinUsb.sys as a USB device’s function driver and how to use the WinUSB API to communicate with the device from an application. The examples in this paper are based on the OSR USB FX2 Learning Kit device, but you can easily extend the procedures to other USB devices. Figure 1 is a simplified diagram of the FX2 device and shows its key features. Figure 1. OSR USB FX2 Learning Kit device Summary of WinUSB, UMDF, and KMDF Capabilities Table 1 summarizes the capabilities of WinUSB, UMDF USB drivers, and KMDF USB drivers. Table 1. WDF USB Feature Support Requirements WinUSB UMDF KMDF Supports multiple concurrent applications. No Yes Yes Isolates driver address space from application address space. No Yes No Supports bulk, interrupt, and control transfers. Yes Yes Yes Supports isochronous transfers. No No Yes Supports the installation of kernel-mode drivers such as filter drivers above the USB driver. No No Yes Supports selective suspend and wait/wake Yes Yes Yes Table 2 summarizes which WDF options are supported by different versions of Windows. Table 2. WDF USB Windows Support Requirements WinUSB UMDF KMDF Windows Vista and later Yes1 Yes1 Yes Windows Server 2003 No No Yes Windows XP Yes2 Yes2 Yes Windows 2000 No No Yes3 Notes: 1WinUSB and UMDF are supported only on x86 and x64 versions of Windows. 2WINUSB and UMDF are supported on Windows XP with service pack 2 or later. 3KMDF is supported on Windows 2000 with Service Pack 4 or later. Guidelines for Providing Access to USB Devices Generally, start with the simplest approach, WinUSB, and move to more complex solutions only if it is necessary. If your device does not support isochronous transfers and is accessed by only a single application, the application can use WinUSB to configure the device and access its endpoints. For example, WinUSB is the preferred approach to use for an electronic weather station that is accessed only by an application that is packaged with the device. WinUSB is also useful for diagnostic communication with a device and for flashing firmware. Some types of devices require a custom function driver. For example, you must implement a driver for devices that are accessed by multiple concurrent applications. The general guidelines for implementing WDF USB drivers are as follows: • UMDF is the preferred approach and is suitable for most USB devices. For example, UMDF drivers are the preferred option for music players or serial dongles. • Devices with features that are not supported by UMDF or that must run on versions of Windows earlier than Windows XP require a KMDF driver. For example, a USB network adapter requires a KMDF driver because the driver’s upper edge must communicate with the kernel-mode network interface device standard (NDIS) stack. Such communication can be done only from kernel mode. KMDF drivers are also required for devices that support isochronous transfers. For a detailed discussion about how to implement UMDF and KMDF drivers, see the Microsoft Press book Developing Drivers with the Windows Driver Foundation or the WHDC ”Windows Driver Foundation” Web page. The rest of this white paper is devoted to WinUSB. Introduction to WinUSB WinUSB consists of two primary components: • WinUsb.sys is a kernel-mode driver that can be installed as either a filter or function driver, above the protocol drivers in a USB device’s kernel-mode device stack. • WinUsb.dll is a user-mode DLL that exposes the WinUSB API. Applications can use this API to communicate with WinUsb.sys when it is installed as a device’s function driver. For devices that do not require a custom function driver, WinUsb.sys can be installed in the device’s kernel-mode stack as the function driver. User-mode processes can then communicate with WinUsb.sys through a set of device I/O control requests. The WinUSB API—exposed by WinUSB.dll—simplifies this communication process. Instead of constructing device I/O control requests to perform standard USB operations—such as configuring the device, sending control requests, and transferring data to or from the device—applications call equivalent WinUSB API functions. Internally, WinUsb.dll uses the data that the application passes to the WinUSB function to construct the appropriate device I/O control request and sends the request to WinUsb.sys for processing. When the request is complete, the WinUSB function passes any information returned by WinUsb.sys—such as data from a read request—back to the calling process. Using the WinUSB API to communicate with a device is much simpler than implementing a driver but has the following corresponding limitations: • The WinUSB API lets only one application at a time communicate with the device. If more than one application must be able to communicate concurrently with a device, you must implement a function driver. • The WinUSB API does not support streaming data to or from isochronous endpoints. Isochronous transfers require a kernel-mode function driver. • The WinUSB API does not support devices that already have kernel-mode support. Examples of such devices include modems and network adaptors, which are supported by the telephony API (TAPI) and NDIS, respectively. • For multifunction devices, you can use the device’s INF to specify either an in-box kernel-mode driver or WinUsb.sys for each USB function separately. However, you can specify only one of these options for a particular function, not both. WinUsb.sys is also a key part of the link between a UMDF function driver and the associated device. WinUsb.sys is installed in the device’s kernel-mode stack as an upper filter driver. An application communicates with the device’s UMDF function driver to issue read, write, or device I/O control requests. The driver interacts with the framework, which passes the request to WinUsb.sys, which processes the request and passes it to the protocol drivers and ultimately to the device. Any response returns by the reverse path. WinUsb.sys also serves as the device stack’s Plug and Play and power owner (PPO). WinUSB FAQ This FAQ answers several common questions about WinUSB. Which versions of Windows support WinUSB? WinUSB is supported by: • All Windows Vista SKUs. • All client SKUs of the 32-bit versions of Windows XP SP2 and later service packs. Note: WinUSB is not native to Windows XP; it must be installed with the WinUSB co installer. For details, see ”How to Install WinUsb.sys as a Function Driver” later in this paper. Which USB features are supported by WinUSB? Table 3 shows which high-level USB features are supported by WinUSB in Windows Vista and Windows XP. Table 3. WinUSB Feature Support Feature Windows XP Windows Vista Device I/O control requests Supported Supported Isochronous transfers Not supported Not supported Bulk, control, and interrupt transfers Supported Supported Selective suspend Supported Supported Remote wake Supported Supported How do I get permission to redistribute WinUSB? WinUSB is included in the Windows Driver Kit (WDK) in the form of a co-installer package, WinUSBCoInstaller.dll. Separate DLLs for x86 and x64 systems are located under the WinDDK/BuildNumber/Redist/Winusb folder. These DLLs are signed. IHVs can redistribute these DLLs. Does WinUSB support the DFU profile for USB devices? Microsoft has not implemented a specific driver for firmware updates. WinUSB does not support host-initiated reset port and cycle port operations. However, some devices expose a vendor-defined control code for initiating a reset. In that case, you can use WinUSB to initiate a reset by sending a control transfer request that contains the vendor-defined control code to the device. For a discussion of how to use WinUSB to send control transfer requests, see “Control Requests” later in this paper. How do I report WinUSB bugs or make feature requests? To report bugs or make feature requests, use http://support.microsoft.com to contact your Microsoft Technical Account Manager or Product Support Engineer. How to Install WinUsb.sys as a Function Driver Before your application can use the WinUSB API to communicate with a device, you must install WinUsb.sys as the device’s function driver. To do so, create a package that includes the following: • The WinUSB co installer, which installs WinUSB on the target system, if necessary. The WDK includes three versions of the co-installer: one for x86 systems, one for x64 systems, and one for Itanium systems. They are all named WinUSBCoInstaller.dll and are located in the appropriate subdirectory of the WinDDK/BuildNumber/redist/winusb folder. • The KMDF co installer, which installs the correct version of KMDF on the target system, if necessary. This co-installer is required because WinUsb.sys depends on KMDF. The version of WinUSB on which this paper is based depends on KMDF version 1.5, and the associated co-installer is WdfCoInstaller01005.dll. The x86 and x64 versions of WdfCoInstaller01005.dll are included with the WDK under the WinDDK/BuildNumber/redist/wdf folder. • An INF that installs WinUsb.sys as the device’s function driver. • A signed catalog file for the package. This file is required to install WinUSB on x64 versions of Windows Vista. For more information on how to create and test signed catalog files, see ”Kernel-Mode Code Signing Walkthrough” on the WHDC Web site. Note: As new WDF versions are released, the co-installer names will change to reflect the WDF version number. For example WDF version 1.7 is currently under development, and the KMDF co-installer for that version is named WdfCoInstaller01007.dll. The following example is a simple INF that installs WinUsb.sys as the function driver for the Fx2 device: [Version] Signature = "Windows NT" Class = MyDeviceClass ClassGuid={78A1C341-4539-11d3-B88D-00C04FAD5171} Provider = %ProviderName% CatalogFile=MyCatFile.cat ; ================== Class section ================== [ClassInstall32] Addreg=MyDeviceClassReg [MyDeviceClassReg] HKR,,,0,%ClassName% HKR,,Icon,,-1 ; ========== Manufacturer/Models sections =========== [Manufacturer] %ProviderName% = MyDevice_WinUSB,NTx86,NTamd64,NTia64 [MyDevice_WinUSB.NTx86] %USB/MyDevice.DeviceDesc% =USB_Install, USB/VID_0547&PID_1002 [MyDevice_WinUSB.NTamd64] %USB/MyDevice.DeviceDesc% =USB_Install, USB/VID_0547&PID_1002 [MyDevice_WinUSB.NTia64] %USB/MyDevice.DeviceDesc% =USB_Install, USB/VID_0547&PID_1002 ; =================== Installation =================== ;[1] [USB_Install] Include=winusb.inf Needs=WINUSB.NT ;[2] [USB_Install.Services] Include=winusb.inf AddService=WinUSB,0x00000002,WinUSB_ServiceInstall ;[3] [WinUSB_ServiceInstall] DisplayName = %WinUSB_SvcDesc% ServiceType = 1 StartType = 3 ErrorControl = 1 ServiceBinary = %12%/WinUSB.sys ;[4] [USB_Install.Wdf] KmdfService=WINUSB, WinUsb_Install [WinUSB_Install] KmdfLibraryVersion=1.5 ;[5] [USB_Install.HW] AddReg=Dev_AddReg [Dev_AddReg] HKR,,DeviceInterfaceGUIDs,0x10000,"{b35924d6-3e16-4a9e-9782-5524a4b79bac}" ;[6] [USB_Install.CoInstallers] AddReg=CoInstallers_AddReg CopyFiles=CoInstallers_CopyFiles [CoInstallers_AddReg] HKR,,CoInstallers32,0x00010000,"WdfCoInstaller01005.dll,WdfCoInstaller","WinUSBCoInstaller.dll" [CoInstallers_CopyFiles] WinUSBCoInstaller.dll WdfCoInstaller01005.dll [DestinationDirs] CoInstallers_CopyFiles=11 ; ================= Source Media Section ===================== ;[7] [SourceDisksNames] 1 = %DISK_NAME%,,,/i386 2 = %DISK_NAME%,,,/amd64 3 = %DISK_NAME%,,,/ia64 [SourceDisksFiles.x86] WinUSBCoInstaller.dll=1 WdfCoInstaller01005.dll=1 [SourceDisksFiles.NTamd64] WinUSBCoInstaller.dll=2 WdfCoInstaller01005.dll=2 [SourceDisksFiles.ia64] WinUSBCoInstaller.dll=3 WdfCoInstaller01005.dll=3 ; =================== Strings =================== [Strings] ProviderName="MyWinUsbTest" USB/MyDevice.DeviceDesc="Test using WinUSB only" WinUSB_SvcDesc="WinUSB Test" DISK_NAME="My Install Disk" ClassName="MyDeviceClass" This INF can be used for most USB devices, with some straightforward modifications. Generally, you should change “USB_Install” in section names to an appropriate DDInstall value. You should also make straightforward changes to the version, manufacturer, and model sections, such as providing an appropriate manufacture’s name, the name of your signed catalog file, the correct device class, and the vendor identifier (VID) and product identifier (PID) for the device. The device-specific values that should be changed are shown in the example in bold. Values that might need to be changed, such as those that depend on version number, are in italic. Note: For more information on USB device classes, see “Supported USB Classes” in the WDK. Apart from device-specific values and several issues that are noted in the following list, you can use these sections and directives without modification to install WinUSB for any USB device. The following notes correspond to the numbered comments in the INF. 1. The Include and Needs directives in the USB_Install section are required for installing WinUSB on Windows Vista systems. Windows XP systems ignore these directives. These directives should not be modified. 2. The Include directive in the USB_Install.Services section includes the system-supplied INF for WinUSB. This INF is installed by the WinUSB co-installer if it is not already on the target system. The AddService directive specifies WinUsb.sys as the device’s function driver. These directives should not be modified. 3. The WinUSB_ServiceInstall section contains the data for installing WinUsb.sys as a service. This section should not be modified. 4. The KmdfService directive in the USB_Install.Wdf section installs WinUsb.sys as a kernel-mode service. The referenced WinUSB_Install section specifies the KMDF library version. This example is based on the Windows Vista version of the WDK (build 6000), which includes KMDF version 1.5. Later versions of WinUSB might require a later KMDF version. 5. USB_Install.HW is the key section in the INF. It specifies the device interface globally unique identifier (GUID) for your device. The AddReg directive puts the interface GUID in a standard registry value. When WinUsb.sys is loaded as the device’s function driver, it reads the registry value and uses the specified GUID to represent the device interface. You should replace the GUID in this example with one that you create specifically for your device. If the protocols for the device change, you should create a new device interface GUID. 6. The USB_Install.CoInstallers section, including the referenced AddReg and CopyFiles sections, contains data and instructions to install the WinUSB and KMDF co installers and associate them with the device. Most USB devices can use these sections and directives without modification. 7. The x86 and x64 versions of Windows have separate co installers. This example stores them on the installation disk in folders that are named i386 and amd64, respectively. Figure 2 (on the following page) shows an example of what an IHV’s driver package might contain. Note: Each co-installer has free and checked versions. Use the free version to install WinUSB on free builds of Windows, including all retail versions. Use the checked version—which has the “_chk” suffix—to install WinUSB on checked builds of Windows. The INF typically also contains directives to install the associated application. You install WinUsb.sys exactly like any other driver. The simplest approach is to plug in the device and use the Add New Hardware Wizard or Device Manager to install the driver by using the INF that is discussed in this section. For more details on INFs and how to install device drivers, see ”Device and Driver Installation” in the WDK. Figure 2. Example driver package contents How to Use the WinUSB API If a USB device has WinUsb.sys as its function driver, the associated application communicates with the device by calling various WinUSB API functions. To use the WinUSB API in an application: • Include WinUsb.h. It is included with the WDK, under WINDDK/BuildNumber/inc/ddk. • Add WinUsb.lib to the list of libraries that are linked to your application. WinUsb.lib is included with the WDK. The version for Windows XP is located under WINDDK/BuildNumber/lib/wxp/i386. There are separate versions of WinUsb.lib for Windows Vista for each supported CPU architecture. They are located under the WINDDK/BuildNumber/lib/wlh folder. • Include Usb100.h, which is also under WINDDK/BuildNumber/inc/ddk. This header is not required, but it contains declarations for some useful macros. To access the device, an application must: 1. Use the device interface GUID to obtain a handle to the device. 2. Use the handle to initialize WinUSB. 3. Use the WinUSB API to configure the device. 4. Use the WinUSB API to communicate with the endpoints. This section shows how to perform these key tasks, based on a simple application that accesses the Fx2 device. Obtain a Handle to the Device and Initialize WinUSB To use the WinUSB API, you must first obtain a file handle for the device and use that handle to initialize WinUSB. The first two steps of the procedure are similar to those steps that are used to obtain a file handle for any device: 1. Use the device interface GUID to obtain the device path. The correct GUID is the one that you specified in the INF that was used to install WinUsb.sys. 2. Use the device path from step 1 to obtain a file handle for the device. 3. Pass the file handle to WinUsb_Initialize to initialize WinUSB and obtain a WinUSB handle. You use the device’s WinUSB handle to identify the device when you call WinUSB API functions, not the device’s file handle. Obtain the Device Path The application’s GetDevicePath function, which is shown in the following example, uses the device interface GUID to obtain the device path. It is similar to the Setup API code that is used for most devices, but is included here for completeness. For more information, see “Setup API” on MSDN. Note that some code—mostly routine error-handling code—has been omitted for clarity: BOOL GetDevicePath(LPGUID InterfaceGuid, PCHAR DevicePath, size_t BufLen) { BOOL bResult = FALSE; HDEVINFO deviceInfo; SP_DEVICE_INTERFACE_DATA interfaceData; PSP_DEVICE_INTERFACE_DETAIL_DATA detailData = NULL; ULONG length; ULONG requiredLength=0; HRESULT hr; // [1] deviceInfo = SetupDiGetClassDevs(InterfaceGuid, NULL, NULL, DIGCF_PRESENT | DIGCF_DEVICEINTERFACE); ...//Error handling code omitted. // [2] interfaceData.cbSize = sizeof(SP_DEVICE_INTERFACE_DATA); bResult = SetupDiEnumDeviceInterfaces(deviceInfo, NULL, InterfaceGuid, 0, &interfaceData); ...//Error handling code omitted. // [3] SetupDiGetDeviceInterfaceDetail(deviceInfo, &interfaceData, NULL, 0, &requiredLength, NULL); detailData = (PSP_DEVICE_INTERFACE_DETAIL_DATA) LocalAlloc(LMEM_FIXED, requiredLength); if(NULL == detailData) { SetupDiDestroyDeviceInfoList(deviceInfo); return FALSE; } detailData->cbSize = sizeof(SP_DEVICE_INTERFACE_DETAIL_DATA); length = requiredLength; bResult = SetupDiGetDeviceInterfaceDetail(deviceInfo, &interfaceData, detailData, length, &requiredLength, NULL); if(FALSE == bResult) { LocalFree(detailData); return FALSE; } // [4] hr = StringCchCopy(DevicePath, BufLen, detailData->DevicePath); if(FAILED(hr)) { SetupDiDestroyDeviceInfoList(deviceInfo); LocalFree(detailData); } LocalFree(detailData); return bResult; } The basic procedure is as follows: 1. Get a handle to the device information set by passing the device interface GUID that you defined in the INF to SetupDiGetClassDevs. The function returns an HDEVINFO handle. 2. Call SetupDiEnumDeviceInterfaces to enumerate the system’s device interfaces and obtain information on your device interface. To do so: • Initialize a SP_DEVICE_INTERFACE_DATA structure by setting its cbSize member to the size of the structure. • Pass the HDEVINFO handle from step 1, the device interface GUID, and a reference to the initialized SP_DEVICE_INTERFACE_DATA structure to SetupDiEnumDeviceInterfaces. • When the function returns, the SP_DEVICE_INTERFACE_DATA structure contains basic data for the interface. 3. Call SetupDiGetDeviceInterfaceDetail to get detailed data for the device interface. The information is returned in a SP_DEVICE_INTERFACE_DETAIL_DATA structure. • Because the size of the SP_DEVICE_INTERFACE_DETAIL_DATA structure varies, you must first obtain the correct buffer size by calling SetupDiGetDeviceInterfaceDetail with the DeviceInterfaceDetailData parameter set to NULL. • The function returns the correct buffer size in the requiredlength parameter. Use that value to correctly allocate memory for a SP_DEVICE_INTERFACE_DETAIL_DATA structure. • Call SetupDiGetDeviceInterfaceDetail again and pass it a reference to the initialized structure. When the function returns, the structure contains detailed information about the interface. 4. The device path is in the SP_DEVICE_INTERFACE_DETAIL_DATA structure’s DevicePath member. Obtain a File Handle for the Device The application’s OpenDevice function, which is shown in the following example, obtains a file handle for the device by passing the device path to CreateFile. 1. Call the GetDevicePath utility function to obtain the device path. GetDevicePath was discussed in the previous section. 2. Pass the device path to CreateFile to obtain a file handle for the device. This example obtains a file handle that supports synchronous read and write access to the device. For details on how to open a file handle for asynchronous I/O, see the “CreateFile Function” reference page on MSDN. Be sure to set the FILE_FLAG_OVERLAPPED flag. WinUSB depends on this setting: HANDLE OpenDevice(BOOL bSync) { HANDLE hDev = NULL; char devicePath[MAX_DEVPATH_LENGTH]; BOOL retVal; retVal = GetDevicePath( (LPGUID) &GUID_DEVINTERFACE_OSRUSBFX2, devicePath, sizeof(deviceName)); ...//Error-handling code omitted. hDev = CreateFile(devicePath, GENERIC_WRITE | GENERIC_READ, FILE_SHARE_WRITE | FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL | FILE_FLAG_OVERLAPPED, NULL); ...//Error-handling code omitted. return hDev; } Initialize WinUSB The handle that was obtained in the preceding section is the file handle for the device. However, the WinUSB API uses a WinUSB handle to identify the target device instead of the file handle. To obtain a WinUSB handle, initialize WinUSB by passing the file handle to WinUsb_Initialize. This function returns the WinUSB handle for the device. The following example initializes WinUSB with the file handle that the OpenDevice utility function obtained, as discussed in the preceding section. It then stores the corresponding WinUSB handle for later use in a privately defined global structure: deviceHandle = OpenDevice(TRUE); bResult = WinUsb_Initialize(deviceHandle, &usbHandle); if(bResult) { devInfo.winUSBHandle = usbHandle; } Configure the Device After an application initializes WinUSB, it must configure the USB device. The procedure is similar to the one that USB device drivers use. However, it is accomplished by calling WinUSB API functions instead of the WDF framework libraries or any of the Windows WDM USB client support routines. The application’s InitializeDevice function, which is shown in the following example, configures the Fx2 device. It also includes the code shown in the preceding example to initialize WinUSB: BOOL Initialize_Device() { BOOL bResult; WINUSB_INTERFACE_HANDLE usbHandle; USB_INTERFACE_DESCRIPTOR ifaceDescriptor; WINUSB_PIPE_INFORMATION pipeInfo; UCHAR speed; ULONG length; deviceHandle = OpenDevice(TRUE); bResult = WinUsb_Initialize(deviceHandle, &usbHandle); //[1] if(bResult) { devInfo.winUSBHandle = usbHandle; length = sizeof(UCHAR); bResult = WinUsb_QueryDeviceInformation(devInfo.winUSBHandle, DEVICE_SPEED, &length, &speed); } //[2] if(bResult) { devInfo.deviceSpeed = speed; bResult = WinUsb_QueryInterfaceSettings(devInfo.winUSBHandle, 0, &ifaceDescriptor); } if(bResult) { for(int i=0;i