TAILIEUCHUNG - USB Complete fourth- P15

USB Complete fourth- P15: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 4 Table 4-14 The device capability descriptor can provide information that is specific to a technology or another aspect of a device or its function. Offset decimal Field Size bytes Description 0 bLength 1 Descriptor length in bytes varies . 1 bDescriptorType 1 DEVICE CAPABILITY 10h 2 bDevCapabilityType 1 01h Wireless USB 02h USB EXTENSION 03h SUPERSPEED_USB 04h CONTAINER ID 00h 05h-FFH reserved 3 Capability-Dependent varies Capability-specific data and format. Microsoft OS Descriptors Microsoft OS descriptors enable storing Windows-specific information. Placing the information in descriptors means the information is available on attachment instead of requiring users to provide the information on separate media. The Microsoft OS string descriptor has an index of EEh and contains an embedded signature. Windows XP SP1 and later request this string descriptor from a device on first attachment. A device that doesn t support the descriptor should return STALL. On retrieving a Microsoft OS string descriptor Windows may request one or more Microsoft OS feature descriptors. The extended compat ID feature descriptor contains Microsoft-defined IDs that can help Windows locate a driver for device functions that don t have Windows-provided drivers. The extended properties feature descriptor can provide text icons and other device-specific properties. Updating Descriptors to USB To update descriptors for a USB device to USB all except some devices that have isochronous endpoints require just one change in the device descriptor bcdUSB must be 0200h or greater. As Chapter 3 explained a USB device s default interface s must request no isochronous bandwidth so an interface that wants to do isochronous transfers must have at least one alternate interface setting and the alternate interface descriptor will have at least one subordinate endpoint descriptor. 116 5 Control Transfers Structured Requests for Critical Data Of USB s four transfer types control .

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