Patent ID: 8793524
Filing Date: 2014-07-29
Classification: G06F,H04L

Abstract:
1. A method of determining a downstream propagation time of signals from a USB Host Controller to a SuperSpeed USB device in a USB network, comprising: opening at least one Isochronous communication pipe between the Host Controller and the SuperSpeed USB device; ensuring that the SuperSpeed USB device is in link state UO in preparation for receiving an Isochronous Timestamp Packet (ITP); controlling the USB Host Controller to send a plurality of Isochronous Timestamp Packets across the Isochronous communication pipe, the Isochronous Timestamp Packets containing respective first timestamps indicative of times at which the Host Controller generated the respective Isochronous Timestamp Packets; frequency locking a local clock of the SuperSpeed USB device according to information derived from a plurality of the Isochronous Timestamp Packets such that the time domain of the local clock of the SuperSpeed USB device is syntonised to the time domain of a local clock of the USB Host Controller; the SuperSpeed USB device transmitting a plurality of signals to the USB Host Controller; creating a second timestamp indicative of a time of reception of the respective signals from the SuperSpeed USB device; determining a time period from one or more respective time differences between corresponding first and second timestamps, the time period being indicative of a sum of a downstream propagation time and an upstream propagation time; and determining the downstream propagation time from the time period and a value of retransmission latency derived from the syntonised local clock of the SuperSpeed USB device.