Cyclemaster synchronization in a distributed bridge

• US 7,987,381 B2
• Filed: 06/19/2007
• Issued: 07/26/2011
• Est. Priority Date: 12/29/2003
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Whitby-Strevens, Colin
• Primary Examiner(s): Cao; Chun
• Application Number:
  US11/820,657
• Publication Number:
  US 20080034245A1
• Time in Patent Office: 1,498 Days
• Field of Search: 713/400, 713/401, 713/600, 370/503
• US Class Current: 713/401
• CPC Class Codes: H04J 3/0655 using timestamps
• CPC Class Codes: H04J 3/0682 by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
• CPC Class Codes: H04L 12/40052 High-speed IEEE 1394 serial bus bus transfer protocol on a daisy chain bus using an embedded synchronisation G06F13/426
• CPC Class Codes: H04L 12/40058 Isochronous transmission
• CPC Class Codes: H04L 12/40091 Bus bridging LAN interconnection over a bridge based backbone H04L12/462; single bridge functionality H04L12/462
• CPC Class Codes: H04N 21/4302 Content synchronisation processes, e.g. decoder synchronisation
• CPC Class Codes: H04N 21/43615 Interfacing a Home Network, e.g. for connecting the client to a plurality of peripherals home Audio Video Interoperability [HAVI] data switching networks H04L12/2805
• CPC Class Codes: H04N 21/43632 involving a wired protocol, e.g. IEEE 1394 high-speed IEEE 1394 serial bus H04L12/40052

Abstract

A method of synchronizing cyclemasters over a distributed bridge is disclosed. The method comprises: a local portal sending a synchronization signal to a peer portal through a bridge fabric upon occurrence of a cycle synchronization event on the local portal; the peer portal sampling its local cycle timer to obtain a sample value when the peer portal receives the synchronization signal; a bridge manager at an upstream portal communicating the sample value to a bridge manager at an alpha portal; the bridge manager at the alpha portal using the sampled time value to compensate for delays through a bridge fabric, calculate the correction to be applied to a cycle timer associated with the alpha portal, and correct the cycle timer.

Claims

1. A computerized system, comprising:

a plurality of buses interconnected by a plurality of bridges, said plurality of bridges comprising a first bridge and a second bridge, the second bridge comprising a first portal;

wherein the first bridge comprises a second portal, a third portal, and a bridge fabric, the first portal in communication with the third portal via the bridge fabric;

wherein the second portal is adapted to receive a cycle synchronization event and upon receiving said event, transmit a synchronization signal through the bridge fabric to the third portal;

wherein the third portal is adapted to receive the synchronization signal, sample a local timer to obtain a sample value, and transmit the sample value to the first portal;

wherein the first portal is adapted to receive the sample value, use the sample value to compensate for at least some delays in transmission over the bridge, and calculate a correction to be applied to a timer associated with the first portal.

2. The system of claim 1, wherein the first portal is adapted to perform said calculation of said correction only when the sample value is received by the first portal within a first time period.

3. The system of claim 1, wherein the first portal comprises an alpha portal, the alpha portal being further adapted to correct the timer associated with the alpha portal if the sample value is received by the alpha portal within the first time period.

4. A bridge device for use with a first portal that is in data communication with a second portal via a bridge fabric, the device comprising:

a first module adapted to measure delays in propagation over the bridge fabric;

a second module adapted to access a timer associated with the first portal, and provide a sample value based at least in part on said access;

a third module adapted to calculate a correction to be applied to a timer associated with a downstream portal if the sample value is provided within a first time period, wherein said correction is based at least in part upon the sample value and upon delays in propagation over the bridge fabric.

5. The bridge device of claim 4, further comprising the downstream portal;

wherein the third module is associated with the downstream portal.

6. The bridge device of claim 4, wherein the second module is further adapted to generate an interrupt when the timer associated with the first portal is sampled.

7. The bridge device of claim 4, further comprising a sample value register, the sample value register adapted to store the sample value.

8. The bridge device of claim 4, wherein the bridge fabric comprises a wireless transmission medium.

9. The bridge device of claim 4, wherein the bridge fabric comprises a protocol adapted to facilitate communications over a local area network.

10. The bridge device of claim 9, wherein the local area network comprises a wireless transmission medium.

11. A bridge device for use with a first portal in data communication with a second portal, comprising:

a first module adapted to generate an error condition if a downstream device does not receive a first sample value and a second sample value within a first time period;

a second module adapted to sample a timer associated with the first portal to obtain the first sample value;

a third module adapted to sample a timer associated with the second portal to obtain the second sample value;

a fourth module adapted to calculate delays in propagation over said bridge device; and

wherein the bridge device is adapted to communicate with software configured to transmit the first sample value and the second sample value to the downstream device.

12. The bridge device of claim 11, further comprising a sample value register, the sample value register adapted to store the first sample value and the second sample value.

13. The bridge device of claim 11, wherein the fourth module is adapted to calculate delays in propagation over said bridge device based at least in part upon the first sample value and the second sample value.

14. The bridge device of claim 11, wherein the bridge device comprises a wireless transmission protocol.

15. The bridge device of claim 11, wherein the bridge device comprises a protocol adapted to facilitate communications over a local area network.

16. The bridge device of claim 11, wherein said bridge device is adapted for use in an IEEE Std. 1394 compliant serial bus network.

17. A computerized system, comprising:

a plurality of buses interconnected by a plurality of bridges, said plurality of bridges comprising a first bridge and a second bridge, the second bridge comprising a first portal;

wherein the first bridge comprises a second portal, a third portal, and a bridge fabric, the first portal in communication with the third portal via the bridge fabric;

wherein the first portal is adapted to perform said calculation of said correction only when the sample value is received by the first portal within a first time period, and indicate an error condition at least when the sample value is not received by the first portal within the first time period;

wherein the second portal is adapted to receive a cycle synchronization event and upon receiving said event, transmit a synchronization signal through the bridge fabric to the third portal;

wherein the third portal is adapted to receive the synchronization signal, sample a local timer to obtain a sample value, and transmit the sample value to the first portal;

wherein the first portal is adapted to receive the sample value, use the sample value to compensate for at least some delays in transmission over the bridge, and calculate a correction to be applied to a timer associated with the first portal.

18. A bridge device for use with a first portal that is in data communication with a second portal via a bridge fabric, the device comprising:

a first module adapted to measure delays in propagation over the bridge fabric;

a second module adapted to access a timer associated with the first portal, and provide a sample value based at least in part on said access;

a third module adapted to calculate a correction to be applied to a timer associated with a downstream portal if the sample value is provided within a first time period, wherein said correction is based at least in part upon the sample value and upon delays in propagation over the bridge fabric; and

a fourth module adapted to indicate an error if the sample value is not successfully provided within the first time period.

19. The bridge device of claim 18, wherein the fourth module is further adapted to indicate an error by setting one or more error flags.

20. A method for bridging a first portal that is in data communication with a second portal via a bridge fabric, comprising:

measuring delays in propagation over the bridge fabric;

accessing a timer associated with the first portal, and

providing a sample value based at least in part on said access;

calculating a correction to be applied to a timer associated with a downstream portal if the sample value is provided within a first time period, wherein said correction is based at least in part upon the sample value and upon delays in propagation over the bridge fabric.

21. The method of claim 20, further comprising the downstream portal;

wherein the third module is associated with the downstream portal.

22. The method of claim 20, additionally comprising generating an interrupt when the timer associated with the first portal is sampled.

23. The method of claim 20, additionally comprising storing a sample value to a sample value register.

24. The method of claim 20, wherein the bridge fabric comprises a wireless transmission medium.

25. The method of claim 20, wherein the bridge fabric comprises a protocol adapted to facilitate communications over a local area network.

26. The method of claim 25, wherein the local area network comprises a wireless transmission medium.