Standard USB Descriptor question

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Hello everybody

  I have been stuck for ages trying to figure out something
in the Standard USB Descriptor during the enumeration. It
looks like it should should be quite simple but I am not
getting it because maybe some mind block, maybe becuase the
documentation is unclear, or maybe because I'm brain-dead.
Here is the problem:

I think the host starts out requesting the device descriptor
This is okay and works no problem. At some point the host
requests the configuration descriptor and I get stuck. The
usb 2.0 spec. says:

"When the host requests the configuration descriptor, all
related interface and endpoint descriptors are returned"

How is the host supposed to know how much data is coming in
or how much data to request until it reads wTotalLength?

I would assume the host would request the 9 bytes of the
configuration descriptor, then make subsequent requests to
get the interfaces and endpoints but for instance in the
section on the interface descriptor the spec says

" An interface descriptor is always returned as part of a
configuration descriptor.

Again how is this supposed happen if the host is only
requesting 9 bytes in the configuration descriptor stage

Bruce
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