USB System Architecture

Hub Local Power Change Request

If software has detected a hub local power status change via the “Get Hub Status” request, software acknowledges the request via the “Clear Hub Local Power Change” request. This request clears the change field so that a subsequent change in the hub local power can be detected.

The “Set Hub Local Power Change Feature” request can be used to set the hub local power status bit, causing the corresponding change bit to be set. Although the specification doesn’t define the use of the this set feature request, it should be useful for debug purposes to simulate a hub local power change. Note that this request cannot be used to acknowledge a change condition.

Hub Over-Current Change Request

The “Set Hub Over-Current Change” request is used to acknowledge a hub over-current condition that has been detected via the “Get Hub Status” request. This request clears the indicator changed bit, thereby making it possible to recognize a subsequent change in the hub over-current indicator.

The “Clear Hub Local Power Change Feature” request sets the over-current indicator, causing the change to be reflected in the corresponding indicator change bit field. As with the “Set Hub Local Power Change” request, this request appears to have been implemented to support debug efforts.

Get Port Status Request

The “Get Port Status” request is defined in the recipient field of the setup transaction. The “Get Hub Status” request defines the recipient as the device (i.e. hub), whereas, the recipient of the “Get Port Status” request is defined as “other” (in this case “other” refers to port). The “index” value defines which port is being selected. The request contains a data stage during which the port status and port change indicators are returned.

Like the hub status information, port status information is returned in four bytes. Two bytes are defined for port status field and two bytes for the port change field.

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