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interface serves a distinct "function", which is typically bound to a different USB device driver. One common example is a USB speaker with an audio interface for playback, and a HID interface for use with software volume control.

Interface descriptor info (can be multiple per Config):

I:If#=dd Alt=dd #EPs=dd Cls=xx(sssss) Sub=xx Prot=xx Driver=ssss

					__Driver name
					or "(none)"
				__InterfaceProtocol
			__InterfaceSubClass
		__InterfaceClass
	__NumberOfEndpoints
__AlternateSettingNumber

__InterfaceNumber __Interface info tag

A given interface may have one or more "alternate" settings. For example, default settings may not use more than a small amount of periodic bandwidth. To use significant fractions

of bus bandwidth, drivers must select a non-default altsetting.

Only one setting for an interface may be active at a time, and only one driver may bind to an interface at a time. Most devices have only one alternate setting per interface.

Endpoint descriptor info (can be multiple per Interface):

E:Ad=xx(s) Atr=xx(ssss) MxPS=dddd Ivl=dddms

		__Interval (max) between transfers
	__EndpointMaxPacketSize
__Attributes(EndpointType)

__EndpointAddress(I=In,O=Out) __Endpoint info tag

The interval is nonzero for all periodic (interrupt or isochronous) endpoints. For high speed endpoints the transfer interval may be measured in microseconds rather than milliseconds.

For high speed periodic endpoints, the "MaxPacketSize" reflects the per-microframe data transfer size. For "high bandwidth" endpoints, that can reflect two or three packets (for up to 3KBytes every 125 usec) per endpoint.

With the Linux-USB stack, periodic bandwidth reservations use the transfer intervals and sizes provided by URBs, which can be less than those found in endpoint descriptor.

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