Cross controller clock synchronization

• US 8,307,235 B2
• Filed: 05/05/2010
• Issued: 11/06/2012
• Est. Priority Date: 05/05/2010
• Status: Active Grant

• Current Assignee: National Instruments Corporation (Emerson Electric Company)
• Original Assignee: National Instruments Corporation (Emerson Electric Company)
• Inventors: Patel, Kunal H., Ullrich, Adam C., Vemishetty, Kalyanramu, Hanssen, Stephen A.
• Primary Examiner(s): Phan, Raymond
• Application Number:
  US12/774,003
• Publication Number:
  US 20110276820A1
• Time in Patent Office: 916 Days
• Field of Search: 713400-401, 713/375, 713500-503
• US Class Current: 713/400
• CPC Class Codes: G06F 1/12 Synchronisation of different clock signals provided by a plurality of clock generators
• CPC Class Codes: H04J 3/0667 Bidirectional timestamps, e.g. NTP or PTP for compensation of clock drift and for compensation of propagation delays arrangements for monitoring round trip delays in packet switching networks H04L43/0864
• CPC Class Codes: H04L 7/0008 Synchronisation information channels, e.g. clock distribution lines

Abstract

A system may include a plurality of subsystems, e.g. instrumentation units housed in separate chassis, each chassis including multiple instrumentation devices, e.g. data acquisition cards. Each subsystem may generate a local reference clock, which may be phase aligned and locked with respect to one or more similar reference clocks of other subsystems, via a high-level precision time protocol (PTP). Each instrumentation device within a given subsystem may generate its own sample clock based on the local reference clock, and may generate its own trigger clock based on its own sample clock. All trigger clocks may be synchronized with respect to each other through a future time event issued using the PTP, and each instrumentation device may then use its trigger clock to synchronize any received trigger pulses, which may also be issued through future time events using the PTP. This results in synchronizing the received triggers across all participating instrumentation devices across all participating subsystems, ensuring that data acquisition is properly synchronized across the multiple subsystems.

Claims

1. A method for synchronizing multiple subsystems with respect to each other, the method comprising:

phase aligning a first master clock signal of a first subsystem to a second master clock signal of a second subsystem;

phase aligning a first slave clock signal of the first subsystem to the first master clock signal, and phase aligning a second slave clock signal of the second subsystem to the second master clock signal;

asserting a first trigger pulse in the first subsystem and a second trigger pulse in the second subsystem at a same first point in time, subsequent to said phase aligning the first master clock signal and said phase aligning the second master clock signal;

receiving the first trigger pulse, and in response to receiving the first trigger pulse;

performing a first function using the first master clock signal; and

performing a second function using the first slave clock signal; and

receiving the second trigger pulse, and in response to receiving the second trigger pulse;

performing a third function using the second master clock signal; and

performing a fourth function using the second slave clock signal;

wherein said performing the first, second, third, and fourth functions begin at a same second point in time.

2. The method of claim 1, further comprising:

generating the first master clock signal based on a first reference clock signal of the first subsystem; and

generating the second master clock signal based on a second reference clock signal of the first subsystem.

3. The method of claim 2, further comprising:

prior to said phase aligning the first master clock signal to the second master clock signal, phase aligning the first reference clock signal to the second reference clock signal.

4. The method of claim 2, further comprising:

generating a first sample clock signal from the first reference clock signal; and

generating a second sample clock signal from the second reference clock signal.

5. The method of claim 2, wherein the first reference clock signal and the second reference clock signal have the same frequency.

6. The method of claim 2, further comprising:

generating the first slave clock signal based on the first reference clock signal; and

generating the second slave clock signal based on the second reference clock signal.

7. The method of claim 3, wherein said phase aligning the first reference clock signal to the second reference clock signal comprises phase aligning the first reference clock signal to the second reference clock signal using a high-level precision time protocol.

8. The method of claim 3, wherein said phase aligning the first master clock signal to the second master clock signal comprises:

aligning the first master clock signal to a specified edge of a specified pulse of the first reference signal, corresponding to a third point in time; and

aligning the second master clock signal to a specified edge of a specified pulse of the second reference signal, corresponding to the third point in time.

9. The method of claim 4, wherein said performing the first function comprises acquiring data samples according to the first sample clock signal, and/or wherein said performing the second function comprises acquiring data samples according to the second sample clock signal.

10. The method of claim 4, wherein the first sample clock signal and the second sample clock signal have different frequencies.

11. The method of claim 4, wherein said generating the first master clock signals comprises generating the first master clock signal from the first sample clock signal, and said generating the second master clock signals comprises generating the second master clock signal from the second sample clock signal;

wherein the first master clock signal and the second master clock signal have the same frequency, which is a common multiple of the frequency of the first sample clock signal and the frequency of the second sample clock signal.

12. The method of claim 7, wherein the high-level precision time protocol is one of:

IEEE-1588 protocol; and

global positioning system protocol.

13. The method of claim 8, further comprising generating a first synchronization pulse in the first subsystem and a second synchronization pulse in the second subsystem at a same fourth point in time;

wherein said aligning the first master clock signal comprises receiving the first synchronization pulse, and in response to receiving the first synchronization pulse adjusting the first master clock signal until it is aligned with the specified edge of the specified pulse of the first reference signal; and

/or

wherein said aligning the second master clock signal comprises receiving the second synchronization pulse, and in response to receiving the first synchronization pulse adjusting the second master clock signal until it is aligned with the specified edge of the specified pulse of the second reference signal.

14. A method for operating multiple subsystems synchronously with respect to each other, the method comprising:

phase aligning a first master clock signal of a first subsystem to a second master clock signal of a second subsystem;

asserting a first trigger pulse in the first subsystem and a second trigger pulse in the second subsystem at a same first point in time, subsequent to said phase aligning the first master clock signal and said phase aligning the second master clock signal;

receiving the first trigger pulse, and in response to receiving the first trigger pulse performing a first function using the first master clock signal; and

receiving the second trigger pulse, and in response to receiving the second trigger pulse performing a second function using the second master clock signal;

wherein said performing the first function and said performing the second function are both started at a same second point in time.

15. The method of claim 14, further comprising:

generating a first reference clock signal in the first subsystem and generating a second reference clock signal in the second subsystem;

generating a first sample clock signal from the first reference signal and generating a second sample clock signal from the second reference signal; and

generating the first master clock signal from the first sample clock signal and generating the second master clock signal from the second sample clock signal.

16. The method of claim 14, wherein said asserting the first trigger pulse comprises asserting the first trigger pulse subsequent and close to a rising edge of a pulse of the first master clock signal corresponding to the first point in time, and wherein said asserting the second trigger pulse comprises asserting the second trigger pulse subsequent and close to a rising edge of a pulse of the second master clock signal corresponding to the first point in time.

17. The method of claim 15, wherein the first reference clock signal and the second reference clock signal have the same frequency;

wherein the first sample clock signal and the second sample clock signal have different frequencies; and

wherein the first master clock signal and the second master clock signal have the same frequency that is a common multiple of the frequency of the first sample clock signal and the frequency of the second sample clock signal.

18. The method of claim 16, further comprising:

generating a first master trigger pulse from the first trigger pulse on a falling edge of the pulse of the first master clock signal corresponding to the first point in time; and

generating a second master trigger pulse from the second trigger pulse on a falling edge of the pulse of the second master clock signal corresponding to the first point in time;

wherein a next pulse of the first master clock signal following the pulse of the first master clock signal corresponding to the first point in time corresponds to the second point in time; and

wherein a next pulse of the second master clock signal following the pulse of the second master clock signal corresponding to the first point in time corresponds to the second point in time.

19. The method of claim 15, further comprising phase aligning the first reference clock signal to the second reference clock signal prior to said phase aligning the first master clock signal to the second master clock signal.

20. A method for synchronizing multiple subsystems with respect to each other, the method comprising:

generating a first reference clock signal in a first subsystem and generating a second reference clock signal in a second subsystem, wherein the first subsystem and the second subsystem are coupled together by a communications channel;

generating a first master clock signal and a second master clock signal;

phase aligning the first reference clock signal to the second reference clock signal using a high-level synchronization protocol over the communications channel;

issuing a first synchronization pulse in the first subsystem and a second synchronization pulse in the second subsystem at a same first point in time;

recognizing the first synchronization pulse, and in response to recognizing the first synchronization pulse, adjusting the first master clock signal to align with a specified edge of a specified pulse of the first reference clock signal corresponding to the first point in time; and

recognizing the second synchronization pulse, and in response to recognizing the second synchronization pulse, adjusting the second master clock signal to align with a specified edge of a specified pulse of the second reference clock signal corresponding to the first point in time;

wherein said adjusting the first master clock signal and said adjusting the second master clock signal result in the first master clock signal and the second master clock signal being phase aligned with respect to each other.

21. The method of claim 20, wherein said generating the first master clock signal comprises generating the first master clock signal based on the first reference clock signal, and wherein said generating the second master clock signal comprises generating the second master clock signal based on the second reference clock signal.

22. The method of claim 20, wherein the first reference clock signal and the second reference clock signal have the same frequency, and wherein the first master clock signal and the second master clock signal have the same frequency.

23. The method of claim 20, further comprising using the first master clock signal and the second master clock signal to recognize start of event triggers, to simultaneously start performing respective functions in the first subsystem and the second subsystem.

24. The method of claim 20, further comprising:

programming a first future time event into the first subsystem via the high-level synchronization protocol; and

programming a second future time event into the second subsystem via the high-level synchronization protocol;

wherein the first future time event comprises said issuing the first synchronization pulse, and wherein the second future time event comprises said issuing the second synchronization pulse.

25. A subsystem comprising:

a timing controller configured to;

generate a reference clock signal;

receive first programming information usable to generate a first future time event at a specified first point in time; and

generate the first future time event at the specified first point in time as instructed by the first programming information, and synchronously with the reference clock signal; and

a first device configured to;

generate a first trigger clock signal;

recognize the first future time event generated by the timing controller, and, responsive to recognizing the first future time event, adjust the first trigger clock signal to phase align the first trigger clock signal to a specified edge of a specified first pulse of the reference clock signal corresponding to the specified first point in time.

26. The subsystem of claim 25, wherein the first device is further configured to:

upon recognizing the first future time event, determine a time delay between the specified edge of the specified pulse of the reference clock signal and a specified edge of a specified pulse of the first trigger clock signal occurring in time after the specified edge of the specified pulse of the reference clock signal; and

adjust the first trigger clock signal based on the determined time delay.

27. The subsystem of claim 25, wherein timing controller is configured issue a synchronization pulse on a specified edge of a specified second pulse of the reference clock signal corresponding to the specified first point in time, as part of generating the first future time event.

28. The subsystem of claim 25, further comprising a subsystem controller configured to:

receive timing information from outside the subsystem;

determine the first programming information based on the received timing information; and

transmit the first programming information to the timing controller.

29. The subsystem of claim 25;

wherein the timing controller is further configured to;

receive second programming information usable to generate a second future time event at a specified second point in time, wherein the specified second point in time corresponds to a first pulse of the first trigger clock signal; and

generate the second future time event at the specified second point in time as instructed by the second programming information;

wherein the first device is further configured to;

recognize the second future time event generated by the timing controller, and as a result of recognizing the second future time event, start performing one or more functions at a specific third point in time occurring in time after the specified second point in time, and synchronously with the first trigger clock signal.

30. The subsystem of claim 27, wherein the first device is configured to recognize the synchronization pulse as part of recognizing the first future time event, and adjust the first trigger clock signal to phase align the first trigger clock signal to the specified edge of the specified first pulse of the reference clock signal in response to recognizing the synchronization pulse.

31. The subsystem of claim 28, wherein the subsystem controller is configured to receive the timing information through a high-level precision time protocol from a system external to the subsystem.

32. The subsystem of claim 29;

wherein the first device is further configured to start performing the one or more functions on a specified edge of a second pulse of the first trigger clock signal corresponding to the specific third point in time.

33. The subsystem of claim 29, wherein timing controller is configured issue a trigger pulse subsequent to the rising edge of the first pulse of the first trigger clock signal, in generating the second future time event.

34. The subsystem of claim 29, wherein the first device is further configured to:

upon recognizing the second future time event, generate a trigger pulse on a specified edge of the first pulse of the first trigger clock signal;

recognize the trigger pulse on a specified edge of a next pulse of the first trigger clock signal occurring after the first pulse of the first trigger clock signal; and

start performing the one or more functions upon recognizing the trigger pulse.

35. The subsystem of claim 29, further comprising a subsystem controller configured to:

receive timing information from outside the subsystem;

determine the first programming information and second programming information based on the received timing information; and

transmit the first programming information and second programming information to the timing controller.

36. The subsystem of claim 29, wherein the one or more functions comprise obtaining data samples.

37. The subsystem of claim 34, further comprising a second device configured to:

generate a second trigger clock signal and align the second trigger clock signal to the first trigger clock signal, the second trigger clock signal thereby having a first pulse occurring at a same point in time as the first pulse of the first trigger clock signal;

recognize the trigger pulse on a specified edge of a next pulse of the second trigger clock signal occurring after the first pulse of the second trigger clock signal; and

start performing one or more functions upon recognizing the trigger pulse.

38. The subsystem of claim 35, wherein the subsystem controller is configured to receive the timing information through a high-level precision time protocol from a system external to the subsystem.

39. A system comprising:

a plurality of subsystems coupled to each other via a communications link, wherein each subsystem of the plurality of subsystems is configured to;

generate a local reference clock signal and a local first trigger clock signal;

receive timing information over the communications link;

based on the received timing information, generate first local programming information usable to generate a first local future time event at a specified first point in time;

generate the first local future time event at the specified first point in time as instructed by the first local programming information, and synchronously with the local reference clock signal; and

recognize the first local future time event, and a result of recognizing the first local future time event adjust the first local trigger clock signal to phase align the first local trigger clock signal to a specified edge of a specified first pulse of the local reference clock signal corresponding to the specified first point in time;

wherein each subsystem phase aligning its respective first local trigger clock signal to the specified edge of the specified first pulse of the subsystem'"'"'s local reference clock signal results in the respective first local trigger clock signals of the plurality of subsystems being phase aligned to each other.

40. The system of claim 39, wherein a first subsystem of the plurality of subsystems is configured to operate as a master subsystem for implementing a high-level precision time protocol, wherein the master subsystem is configured to generate and transmit the timing information to each of the remaining subsystems of the plurality of subsystems.