System and method for time synchronizing nodes in an automotive network using input capture

• US 7,593,429 B2
• Filed: 12/17/2004
• Issued: 09/22/2009
• Est. Priority Date: 10/14/2004
• Status: Active Grant

• Current Assignee: Continental Automotive Systems, Inc. (Continental AG)
• Original Assignee: Temic Automotive of North America, Incorporated (Continental AG)
• Inventors: Johnson, Hugh W., Kartha, Prakash U., Jordan, Patrick D., Dong, Hai
• Primary Examiner(s): Patel; Ajit
• Application Number:
  US11/014,936
• Publication Number:
  US 20060083264A1
• Time in Patent Office: 1,740 Days
• Field of Search: 370/359, 370/503, 370/509, 370/510, 370/511, 370/512, 370/513, 370/514, 370/516, 375/354, 375/356, 375364-366, 375/371
• US Class Current: 370/503
• CPC Class Codes: H04J 3/0664 unidirectional 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 12/403 with centralised control, e.g. polling

Abstract

A system and method for time synchronizing nodes in a switch fabric network of a vehicle. The network has a plurality of nodes that are joined by communication links for the transmission of data there between. Each node of the switch fabric may include a processor, a memory, a clock, a transceiver, and an input capture. The memory is adapted to store and retain timer offsets associated with communication links with neighboring nodes. The transceiver is adapted to transmit and receive synchronization messages between the node and neighboring nodes. The input capture is adapted to capture a timestamp associated with the transmission of synchronization messages. The processor is configured to compute the timer offsets associated with the communication links with neighboring nodes based on the captured timestamps by the input capture function. The computed offsets may then be broadcast and stored by the nodes for subsequent use in time synchronizing data packets through the switch fabric network.

Claims

1. A method for time synchronizing nodes in a switch fabric of a vehicle communication network, the nodes in the switch fabric joined by communication links for the transmission of data packets there between, the method comprising the steps of:

transmitting an initial synchronization message from a first node to a second node;

transmitting an acknowledge ready message from the second node to the first node;

transmitting a reference synchronization message from the first node to the second node;

capturing a first timestamp associated with the reference synchronization message at the first node and a second timestamp associated with the reference synchronization message at the second node;

transmitting the second timestamp from the second node to the first node;

computing an offset in the first node based on the first timestamp captured at the first node and the second timestamp transmitted from the second node; and

storing the offset in the first node for subsequent use in time synchronizing data packets transmitted by the first node to other nodes in the switch fabric.

2. The method in claim 1 further comprising the step of transmitting the first timestamp from the first node to the second node and computing a second offset in the second node based on the second timestamp captured at the second node and the first timestamp transmitted from the first node.

3. The method in claim 1 further comprising the step of transmitting the computed offset from the first node to other nodes in the switch fabric.

4. The method in claim 2 further comprising the step of transmitting the computed second offset from the second node to other nodes in the switch fabric.

5. The method in claim 1, wherein the step of storing the offset includes storing the offset in an offset table, the offset table including a listing of a plurality of offsets of different communication segments between nodes in the switch fabric.

6. The method in claim 1 further comprising the step of receiving an offset at the first node from a third node in the switch fabric, the offset received from the third node being associated with a communication link between the third node and a fourth node.

7. The method in claim 6 further comprising the step of determining a drift rate associated with the third node based on the offset received from the third node.

8. The method in claim 1 wherein the recited steps are performed during a first time and a second time to compute a first offset and a second offset, the method further comprising the step of determining a drift rate based on the first and second offsets and the first and second times.

9. A method for time synchronizing a switch fabric of a vehicle communication network, the switch fabric having at least a first node and a second node, the first node and the second node joined by a communication link for the transmission of data packets there between, the method comprising the steps of:

initiating a synchronization dialogue between the first node and the second node;

designating the first node as the initiator of the synchronization dialogue and the second node as the receiver of the synchronization dialogue;

transmitting a synchronization message from the first node to the second node;

capturing a first timestamp associated with the reference synchronization message at the first node and a second timestamp associated with the reference synchronization message at the second node;

transmitting the second timestamp from the second node to the first node;

computing an offset in the first node based on the first timestamp captured at the first node and the second timestamp transmitted from the second node.

10. The method in claim 9 further comprising the step of storing the offset in the first node for subsequent use in time synchronizing data packets transmitted by the first node to another node along a communication path that includes the second node.

11. The method in claim 9 further comprising the step of transmitting the first timestamp from the first node to the second node and computing a second offset in the second node based on the second timestamp captured at the second node and the first timestamp transmitted from the first node.

12. The method in claim 11 further comprising the step of storing the second offset in the second node for subsequent use in time synchronizing data packets transmitted by the second node to another node along a communication path that includes the first node.

13. The method in claim 9 wherein the switch fabric includes a third node, the method further comprising the step of transmitting the computed offset from the first node to the third node in the switch fabric.

14. The method in claim 11 wherein the switch fabric includes a third node, the method further comprising the step of transmitting the computed second offset from the second node to the third node in the switch fabric.

15. The method in claim 10, wherein the step of storing the offset in the first node includes storing the offset in an offset table, the offset table including a listing of a plurality of offsets of different communication segments between different nodes in the switch fabric.

16. The method in claim 9 wherein the switch fabric includes a third node and a fourth node, the method further comprising the step of receiving an offset at the first node from the third node, the offset received from the third node being associated with a communication link between the third node and the fourth node.

17. The method in claim 16 further comprising the step of determining in a first node a drift rate associated with the third node based on the offset received from the third node.

18. The method in claim 9 wherein the recited steps are performed during a first time and a second time to compute a first offset and a second offset, the method further comprising the step of determining a drift rate based on the first and second offsets and the first and second times.

19. A vehicle network comprising:

a plurality of nodes joined by communication links for the transmission of data there between;

each node of the vehicle network including a processor, a memory, and a clock, the memory adapted to store and retain a timer offset associated with a communication link between the node and a neighboring node;

a transceiver disposed within each node, the transceiver being adapted to transmit synchronization messages to the neighboring node in the vehicle network when the node is an initiator of a synchronization dialogue and being adapted to receive synchronization messages from the neighboring node in the vehicle network when the node is not the initiator of the synchronization dialogue; and

an input capture to capture a timestamp associated with the transmission of synchronization messages when the node is an initiator of the synchronization dialogue and a timestamp associated with the transmission of synchronization messages by the neighboring node when the node is not an initiator of the synchronization dialogue;

wherein the processor is operable to compute the timer offset based on the timestamp captured by the input capture and a neighboring timestamp received from the neighboring node.

20. The vehicle network in claim 19, wherein the transceiver is further adapted to transmit an initial synchronization message to the neighboring node and adapted to receive an acknowledge ready message from the neighboring node when it is the initiator of a synchronization dialogue.

21. The vehicle network in claim 20, wherein the transceiver is further adapted to transmit a reference synchronization message upon receipt of the acknowledge ready message from the neighboring node and adapted to receive the neighboring timestamp from the neighboring node.

22. The vehicle network in claim 19, wherein the transceiver is further adapted to transmit the timer offset to other nodes in the vehicle network.