Setup请求结构体

Offset	Field	Size	Type	Description
0	bmRequestType	1	Bitmap	*D[7] : Data transfer direction The value of this bit is ignored when wLength is zero 0b = Host-to-device 1b = Device-to-host D[6:5] : Type of request 00b = Standard 01b = Class 10b = Vendor 11b = Reserved D[4:0] : Recipient** 00000b = Device 00001b = Interface 00010b = Endpoint 00011b = Other 00100b to 11111b = Reserved
1	bRequest	1	Value	Specific request
2	wValue	2	Value	Word-sized field the may (or may not) serve as a parameter to the request, depending on the specific request.
4	wIndex	2	Index or offset	Word-sized field that may (or may not) serve as a parameter to the request, depending on the specific request. Typically this field holds an index or an offset value.
6	wLength	1	Count	Number of bytes to transfer if there is a DATA stage. * If this field is non-zero, and bmRequestType indicates a transfer from device-to-host, then the device must never return more than wLength bytes of data. However, a device may return less. * If this field is non-zero, and the bmRequestType indicates a transfer from host-to-device, then the host must send exactly wLength bytes of data. If the host sends more than wLength bytes, the behavior of the device is undefined.Number of bytes to transfer if there is a DATA stage.

Set Interface Request Values For Audio Class

Offset	Field	Size	Value	Description
0	bmRequestType	1	0x01	D7: 0 = Host to Device. D6..5: 00 = Standard Request. D4..0: 00001 = Recipient is interface.
1	bRequest	1	0x0B	SET_INTERFACE.
2	wValue	2	0x0000 or 0x0001	0x00 is zero bandwidth alternate setting. 0x01 is normal isochronous operation.
4	wIndex	2	0x0001 or 0x0002	Interface number of one of the AudioStreaming interfaces.
6	wLength	2	0x0000	No Parameter Block

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