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Wed May 23 18:28:21 EDT 2012

Got a USB sniffer

First thing I see with the beagle[1] is that there is traffic that is
not just the device visible on the line.  Does a HUB send stuff to all
ports without being smart about where the devices are?

From [2] it seems that hubs just forward to all ports:

  "During normal transmission, hubs are essentially transparent: data
  received from its upstream port is broadcast to all devices attached
  to its downstream ports; data received from a downstream port is
  generally forwarded to the upstream port only."

and only for insertion there's a brief communication with host to
perform the reset signalling:

  "Hubs are not transparent when dealing with changes in the status of
  downstream ports, such as insertion or removal of devices. In
  particular, if a downstream port of a hub changes status, this
  change is dealt with in an interaction between the host and this
  hub; the hubs between them act as transparent in this case."

[1] http://www.totalphase.com/products/beagle_usb12/
[2] http://en.wikipedia.org/wiki/USB_hub



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