Distributed synchronization and timing system

Abstract

A method and apparatus for controlling the phase and frequency of the local clock of a USB device, the apparatus comprising circuitry for observing USB traffic and decoding from the USB traffic a periodic data structure containing information about the frequency and phase of a distributed clock frequency, and phase and circuitry for receiving the periodic data structure and generating from at least the periodic data structure a local clock signal locked in both frequency and phase to the periodic data structure. The circuitry for receiving the periodic data structure and generating the local clock signal can generate the local clock signal with a frequency that is a non-integral multiple of a frequency of the periodic data structure.

1 - 93 . (canceled) 
     
     
         94 . A real-time synchronous multichannel USB system, comprising:
 a plurality of USB devices attached to a USB network, each USB device comprising a respective local clock, said respective local clocks of said USB devices being synchronized to each other; and   each USB device further comprising a respective absolute time register containing a common notion of real time;   wherein each respective absolute time register is clocked by said respective synchronous local clock.   
     
     
         95 . A USB system as claimed in  claim 94 , adapted to provide real-time synchronization based on a signal received from a USB device attached to said USB network. 
     
     
         96 . A USB system as claimed in  claim 95 , adapted to provide real-time synchronization based on signals from a composite USB hub and a USB device attached to said USB network. 
     
     
         97 . A USB system as claimed in  claim 94 , adapted to provide real-time synchronization based on a signal from an external device adapted to observe USB traffic and provide information to a USB host system controller of said USB network. 
     
     
         98 . A USB system as claimed in  claim 94 , wherein said absolute time registers are synchronized to a common notion of real time of a real-time clock of a host computing or other system. 
     
     
         99 . A USB system as claimed in  claim 94 , wherein said absolute time registers are synchronized to a common notion of real time of a real-time clock on one or more of said plurality of USB devices. 
     
     
         100 . A USB system as claimed in  claim 94 , wherein said absolute time registers are synchronized to common notion of real time of an external time reference. 
     
     
         101 . A USB system as claimed in  claim 100 , wherein said external time reference is adapted to synchronize to a global positioning system (GPS) satellite-based navigation and timing system, complies with IEEE-1588 precision time protocol across Ethernet, or is provided by a time standard or protocol. 
     
     
         102 . A method of providing a real-time synchronous multichannel USB system, comprising:
 synchronizing respective local clocks of each of a plurality of USB devices attached to a USB network;   providing a common notion of real time to respective absolute time registers of each of said USB devices; and   clocking said absolute time registers by the respective local clock.   
     
     
         103 . A method as claimed in  claim 102 , including:
 setting said respective local absolute time register of each of said USB devices to a predefined value at a moment of synchronization; and   recording the real time of said moment of synchronization for each of said plurality of USB devices by a USB system controller.   
     
     
         104 . A method as claimed in  claim 103 , including synchronizing each of said USB devices substantially simultaneously. 
     
     
         105 . A method as claimed in  claim 103 , including synchronizing each of said USB devices sequentially. 
     
     
         106 . A method of assigning a real time to a synchronized USB network, comprising:
 observing USB traffic;   synchronizing a local clock of a synchronization device to carrier signals within said USB traffic;   observing an external time event;   latching a value of an external time-stamp that corresponds to said external time event into a local register;   initiating a local counter;   monitoring a USB data stream local to said synchronization device for carrier signals;   generating a signal to stop said local counter on receipt of a next carrier signal;   detecting a frame number associated with said next carrier signal; and   reporting a value of said local counter, said frame number and said value of said time-stamp to a host system;   said host system assigning a real time to the synchronized USB network for the frame number using the value of said local counter and the value of said time-stamp.   
     
     
         107 . A method as claimed in  claim 106 , comprising determining a time of receipt of the carrier signal that stopped said local counter; 
     
     
         108 . A method as claimed in  claim 107 , comprising:
 determining a period between receipt of said external time event and said numbered carrier signal.   
     
     
         109 . A method as claimed in  claim 108 , including determining said period from a number of clock cycles of said local clock between receipt of said external time event and of said numbered carrier signal and from the period of said local clock. 
     
     
         110 . A method as claimed in  claim 106 , including clocking said local counter by said synchronized local clock or by an external reference clock. 
     
     
         111 . A method as claimed in  claim 106 , wherein said synchronization device comprises a USB device or a composite USB hub and USB device function. 
     
     
         112 . A method as claimed in  claim 106 , wherein said synchronization device is a non-USB device configured to observe USB data traffic and pass information to a host system controller via another information channel. 
     
     
         113 . A USB device for generating an accurate time-stamp of a real-time external event, comprising:
 a local clock synchronized to carrier signals within USB traffic;   a real-time counter register calibrated with a notion of real time, and clocked by said local clock;   an event detector for detecting said real-time external event;   a data latch for latching a value of said real time counter register on detection of said real-time external event; and   a data link to a USB system controller for transmitting a time stamp corresponding to said value of said real time counter register on detection of said real-time external event.   
     
     
         114 . A method of generating an accurate time-stamp of a real-time external event in a synchronized USB network, comprising:
 synchronizing a local clock of a USB device;   calibrating a real time counter with a notion of real time;   clocking said real time counter using said local clock;   detecting said real-time external event;   latching the value of said real time counter on detection of said real-time external event and outputting a corresponding time-stamp; and   transferring said time stamp to a USB system controller of said USB network.   
     
     
         115 . A synchronized USB system adapted to generate an accurate time-stamp of a real-time external event, comprising:
 circuitry adapted to synchronize a local clock of a USB device;   circuitry adapted to calibrate a real time counter with a notion of real time;   circuitry for clocking said real time counter using said local clock;   a detector for detecting said real-time external event; and   a latch for latching the value of said real time counter on detection of said real-time external event, outputting a corresponding time stamp and directing said time stamp to a USB system controller of said USB system.