Clock synchronization across an interface with an intermittent clock signal

• US 8,745,430 B2
• Filed: 04/27/2011
• Issued: 06/03/2014
• Est. Priority Date: 04/27/2011
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Cornelius, William P., Ferry, William O., Jones, Girault W.
• Primary Examiner(s): Rehman, Mohammed
• Assistant Examiner(s): CHANG, VINCENT WEN-LIANG
• Application Number:
  US13/095,607
• Publication Number:
  US 20120278645A1
• Time in Patent Office: 1,133 Days
• Field of Search: None
• US Class Current: 713/400
• CPC Class Codes: G06F 1/12 Synchronisation of different clock signals provided by a plurality of clock generators

Abstract

The disclosed embodiments provide a system that facilitates synchronization between a first component and a second component connected to the first component via an interface in a computer system. During an active state of the interface, the system uses a local time base in the second component to generate a local clock signal that tracks a host clock signal from the first component. Next, during an inactive state of the interface, the system uses the local time base to maintain the local clock signal at the second component. Finally, during a subsequent active state of the interface after the inactive state, the system adjusts the local clock signal to remove clock drift between the local clock signal and the host clock signal.

Claims

1. A method for facilitating synchronization between a first component and a second component connected to the first component via an interface in a computer system, comprising:

during an active state of the interface, using a local time base in the second component to generate a local clock signal that tracks a host clock signal from the first component, wherein the local time base includes a phase-locked loop, which includes a phase comparator that determines a phase difference between the host clock signal and the local clock signal, wherein the phase difference feeds through a filter to produce tuning parameters that feed into a phase accumulator, which is part of a numerically controlled oscillator (NCO) that also receives a timing signal from a local oscillator to produce the local clock signal;

during an inactive state of the interface when the host clock signal becomes inactive, using the local time base to maintain the local clock signal at the second component by halting the feeding of the tuning parameters into the phase accumulator so that the local clock signal is effectively decoupled from the host clock signal; and

during a subsequent active state of the interface when the host clock signal becomes active again, starting the feeding of the tuning parameters into the phase accumulator so that the local clock signal resumes tracking the host clock signal, and adjusting the local clock signal to remove clock drift between the local clock signal and the host clock signal.

2. The method of claim 1, wherein adjusting the local clock signal to remove clock drift between the local clock signal and the host clock signal involves:

calculating the clock drift based on at least one of a phase difference, a frequency difference, and an absolute time difference between the local clock signal and the host clock signal;

obtaining one or more lock settings associated with adjustment of the local clock signal; and

adjusting a frequency of the local clock signal based on the clock drift and the lock settings.

3. The method of claim 2, wherein each of the lock settings is associated with at least one of:

a synchronization time;

a frequency deviation; and

a smoothness parameter.

4. The method of claim 2, wherein the frequency is adjusted in an open loop or a closed loop.

5. The method of claim 1, wherein the NCO comprises:

a microelectromechanical systems (MEMS) oscillator; and

a frequency synthesizer.

6. The method of claim 1,

wherein the first component corresponds to a motherboard, and

wherein the second component corresponds to a peripheral component.

7. The method of claim 1, wherein the local clock signal facilitates at least one of:

synchronization of an audio signal to a video signal; and

synchronization of multiple audio streams.

8. A system for facilitating synchronization between a first component and a second component connected to the first component via an interface in a computer system, comprising:

a local time base in the second component; and

a control apparatus configured to;

during an active state of the interface, use the local time base to generate a local clock signal that tracks a host clock signal from the first component, wherein the local time base includes a phase-locked loop, which includes a phase comparator that determines a phase difference between the host clock signal and the local clock signal, wherein the phase difference feeds through a filter to produce tuning parameters that feed into a phase accumulator, which is part of a numerically controlled oscillator (NCO) that also receives a timing signal from a local oscillator to produce the local clock signal;

during an inactive state of the interface when the host clock signal becomes inactive, use the local time base to maintain the local clock signal at the second component by halting the feeding of the tuning parameters into the phase accumulator so that the local clock signal is effectively decoupled from the host clock signal; and

during a subsequent active state of the interface when the host clock signal becomes active again, starting the feeding of the tuning parameters into the phase accumulator so that the local clock signal resumes tracking the host clock signal, and adjust the local clock signal to remove clock drift between the local clock signal and the host clock signal.

9. The system of claim 8, wherein adjusting the local clock signal to remove clock drift between the local clock signal and the host clock signal involves:

calculating the clock drift based on at least one of a phase difference, a frequency difference, and an absolute time difference between the local clock signal and the host clock signal;

obtaining one or more lock settings associated with adjustment of the local clock signal; and

adjusting a frequency of the local clock signal based on the clock drift and the lock settings.

10. The system of claim 9, wherein each of the lock settings is associated with at least one of:

a synchronization time;

a frequency deviation; and

a smoothness parameter.

11. The system of claim 9, wherein the frequency is adjusted in an open loop or a closed loop.

12. The system of claim 8, wherein the NCO comprises:

a microelectromechanical systems (MEMS) oscillator; and

a frequency synthesizer.

13. The system of claim 8,

wherein the first component corresponds to a motherboard, and

wherein the second component corresponds to a peripheral component.

14. The system of claim 13, wherein the peripheral component is a graphics card.

15. The system of claim 8, wherein the local clock signal facilitates at least one of:

synchronization of an audio signal to a video signal; and

synchronization of multiple audio streams.

16. A non-transitory computer-readable storage medium storing instructions that when executed by a computer cause the computer to perform a method for facilitating synchronization between a first component and a second component connected to the first component via an interface in a computer system, the method comprising:

during an active state of the interface, using a local time base in the second component to generate a local clock signal that tracks a host clock signal from the first component, wherein the local time base includes a phase-locked loop, which includes a phase comparator that determines a phase difference between the host clock signal and the local clock signal, wherein the phase difference feeds through a filter to produce tuning parameters that feed into a phase accumulator, which is part of a numerically controlled oscillator (NCO) that also receives a timing signal from a local oscillator to produce the local clock signal;

during an inactive state of the interface when the host clock signal becomes inactive, using the local time base to maintain the local clock signal at the second component by halting the feeding of the tuning parameters into the phase accumulator so that the local clock signal is effectively decoupled from the host clock signal; and

during a subsequent active state of the interface when the host clock signal becomes active again, starting the feeding of the tuning parameters into the phase accumulator so that the local clock signal resumes tracking the host clock signal, and adjusting the local clock signal to remove clock drift between the local clock signal and the host clock signal.

17. The non-transitory computer-readable storage medium of claim 16, wherein adjusting the local clock signal to remove clock drift between the local clock signal and the host clock signal involves:

calculating the clock drift based on at least one of a phase difference, a frequency difference, and an absolute time difference between the local clock signal and the host clock signal;

obtaining one or more lock settings associated with adjustment of the local clock signal; and

adjusting a frequency of the local clock signal based on the clock drift and the lock settings.

18. The non-transitory computer-readable storage medium of claim 17, wherein each of the lock settings is associated with at least one of:

a synchronization time;

a frequency deviation; and

a smoothness parameter.

19. The non-transitory computer-readable storage medium of claim 17, wherein the frequency is adjusted in an open loop or a closed loop.

20. The non-transitory computer-readable storage medium of claim 16, wherein the NCO comprises:

a microelectromechanical systems (MEMS) oscillator; and

a frequency synthesizer.

21. The non-transitory computer-readable storage medium of claim 16,

wherein the first component corresponds to a motherboard, and

wherein the second component corresponds to a peripheral component.

22. The non-transitory computer-readable storage medium of claim 16, wherein the local clock signal facilitates at least one of:

synchronization of an audio signal to a video signal; and

synchronization of multiple audio streams.