Method and apparatus for synchronising the local time of a plurality of instruments

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 U0 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;
• locking a local clock of the SuperSpeed USB device to information that comprises the first timestamp, derived from one or more of the Isochronous Timestamp Packets, the locking being in respect of frequency such that the local clock is syntonised to a timebase of the USB Host Controller and a notion of time of the local clock is substantially synchronised to a notion of time of the USB Host Controller but with a phase delay equal to an average downstream propagation time of the plurality of Isochronous Timestamp Packets from the USB Host Controller to the SuperSpeed USB device;
• the SuperSpeed USB device transmitting a plurality of signals to the USB Host Controller, each of the signals containing a second timestamp indicative of a local time in the time domain of the SuperSpeed USB device when the respective signal was generated by the SuperSpeed device;
• creating a third 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 second and third 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.

An apparatus for determining the relative downstream propagation time of signals from a USB Host Controller to a SuperSpeed USB device, the apparatus comprising:

• a SuperSpeed-capable upstream port adapted to provide a SuperSpeed upstream connection and a non-SuperSpeed upstream connection;
• a plurality of SuperSpeed-capable downstream ports;
• first circuitry, adapted to perform a USB hub function providing connectivity to said upstream port and said downstream ports for both SuperSpeed and non-SuperSpeed connections;
• second circuitry, adapted to perform one or more SuperSpeed or non-SuperSpeed USB device functions, and connected to at least one of said downstream ports;
• third circuitry, adapted to decode synchronisation information from either the SuperSpeed or the non-SuperSpeed upstream connection;
• a local measurement clock synchronised to a notion of time of the USB Host Controller with the third circuitry;
• and
• fourth circuitry, adapted to monitor SuperSpeed USB traffic for a timestamp signal with a first timestamp received at one of the downstream ports;
• fifth circuitry, adapted to create a second timestamp corresponding to detection of the timestamp signal;
• sixth circuitry, adapted to decode the first timestamp from the SuperSpeed USB traffic corresponding to a data packet or packets for which the second timestamp was generated;
• and
• seventh circuitry or a computational mechanism, adapted to determine a time difference between said first and second timestamps in the time domain of the local measurement clock.

A method of determining the downstream propagation time of signals from a selected point in a USB network across one or more USB cables and one or more USB Hubs to a first SuperSpeed USB device of a plurality of SuperSpeed USB devices, the method comprising:

• ensuring that said first SuperSpeed USB device is in link state U0;
• ensuring that said SuperSpeed USB devices other than said first SuperSpeed USB device are not in link state U0;
• ensuring that no request is made to change the link state of any links in a USB network branch spanned by said selected point and said first SuperSpeed USB Device;
• performing a plurality of round trip propagation time measurements for said first SuperSpeed USB device.

A method of synchronising the operation of a plurality of SuperSpeed USB devices with respective local clocks in a USB network, comprising:

• syntonising the local clocks of said SuperSpeed USB devices;
• synchronising, or phase aligning, respective notions of time of said local clocks;
• and
• maintaining syntonisation of said local clocks, and thereby a synchronous notion of time;
• wherein syntonising said local clocks comprises locking said local clocks either to a periodic data structure in said USB data stream or to a SuperSpeed USB Isochronous Timestamp Packet;
• whereby said SuperSpeed USB devices are synchronised and adapted to enable coordinated operation of a plurality of functions on said SuperSpeed USB devices, synchronised to a common time domain.

A method of synchronising the operation of a plurality of devices with respective local clocks, said devices being attached to a common bus, comprising:

• syntonising the local clocks of said devices;
• synchronising respective notions of time of said local clocks;
• and
• maintaining syntonisation of the local clocks, and thereby a synchronous notion of time of said local clocks;
• whereby said devices are synchronised and adapted to enable coordinated operation of a plurality of functions on said plurality of devices.