tailieunhanh - USB Complete fourth- P16

USB Complete fourth- P16: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 5 Get Status Purpose The host requests the status of the features of a device interface or endpoint. Request Number bRequest 00h Source of Data device Data Length wLength 0002h Contents of wValue field 0000h Contents of wIndex field For a device 0000h. For an interface the interface number. For an endpoint the endpoint number. Contents of data packet in the Data stage the device interface or endpoint status. Supported states Default undefined. Address OK for address zero endpoint zero. Otherwise the device returns STALL. Configured OK. Behavior on error The device returns STALL if the target interface or endpoint doesn t exist. Comments For requests directed to devices operating at USB speeds two status bits are defined. Bit zero is the Self-Powered field 0 bus-powered 1 self-powered. The host can t change this value. Bit 1 is the Remote Wakeup field. The default on reset is zero disabled . SuperSpeed devices support the Self-Powered bit and use bits 2 4 for power-management options. Bit 2 1 means the device is enabled to initiate U1 entry. Bit 3 1 means the device is enabled to initiate U2 entry. Bit 4 1 means the device is enabled to send Latency Tolerance Messages. For request directed to the first interface in a function on a USB bus bit 0 1 if the function supports remote wakeup and bit 1 1 if the host has enabled the function for remote wakeup. For requests directed to an interface on a USB bus all bits are reserved. For requests directed to an endpoint only bit zero is defined. Bit 0 1 indicates a Halt condition. See Set Feature and Clear Feature for more about Remote Wakeup and Halt. All non-assigned bits are reserved. 126 Control Transfers Structured Requests for Critical Data Clear Feature Purpose The host requests to disable a feature on a device interface or endpoint. Request Number bRequest 01h. Source of Data no Data stage Data Length wLength 0000h Contents of wValue field the feature to disable Contents of wIndex field For a .