TAILIEUCHUNG - USB Complete fourth- P23

USB Complete fourth- P23:This book focuses on Windows programming for PCs, but other computers and operating systems also have USB support, including Linux and Apple Computer’s Macintosh. Some real-time kernels also support USB. | Chapter 7 requests the host to send a class-specific Get_Extended_Event_Data request for more information about an event. A device using the bulk-only protocol cancels a transfer by stalling the bulk endpoints. The host then sends a class-specific Get_Device_Status request and uses the Clear Feature request to clear the stalled endpoints. The host cancels a transfer by sending a class-specific Cancel_Request request. A device is ready to resume data transfers when it returns OK PIMA 15740 Response Code 2001h in response to a Get_Device_Status request. Descriptors In an interface descriptor bInterfaceClass 06h to indicate a still-image device bInterfaceSubclass 01h to indicate an image interface and bInterfaceProtocol 01h to indicate a still-image capture function. The interface must have descriptors for the bulk IN bulk OUT and interrupt IN endpoints. Class-specific Requests The class defines four control requests. Cancel_Request requests to cancel the PIMA 15740 transaction named in the request. Get_Extended_Event_Data optional requests extended information regarding an event or vendor condition. Device_Reset_Request requests the device to return to the Idle state. The host can use this request after a bulk endpoint has returned a STALL or to clear a vendor-specific condition. Get_Device_Status requests information needed to clear halted endpoints. The host uses this request after a device has canceled a data transfer. Chips Just about any non-low-speed USB controller will have the three endpoints required by the still-image class. Windows Support Recent Windows editions support the Windows Image Acquisition WIA API for communicating with devices in the still-image class. Applications communicate with devices by using ReadFile WriteFile and DeviceIoControl commands. The driver adds USB support to WIA in Windows XP and later. Beginning with Windows XP cameras that use the Picture Transfer Protocol defined in PIMA 15740 require no vendor-provided driver

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