CAN Bus Clock Drift Prevention via Master-Slave Sync
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Solution Overview
Problem
In distributed CAN systems used in vehicles, clock drift among ECU nodes leads to message loss, and existing solutions like oversampling or digital clock synchronization are either resource-intensive or have high overhead, making them impractical for preventing sequence message losses.
Innovation Solution
The method categorizes nodes into master and slave types, with the master node sending synchronization frames to adjust the task activation periods of slave nodes using a determined synchronization frequency, modeled as a linear hybrid automaton, to prevent message loss while minimizing overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If oversampling is used to prevent message loss, then a single message loss can be compensated, but sequence of message losses cannot be overcome and resource consumption increases significantly
Solution Approach 1:
The system performs preliminary clock synchronization by sending synchronization frames from master nodes to slave nodes at predetermined intervals. This preliminary action aligns the task activation clocks before message transmission occurs, preventing message loss due to clock drift without requiring continuous high-speed oversampling of all messages.
Solution Approach 2:
The CAN system is segmented into master nodes and slave nodes with distinct roles. Master nodes send synchronization frames while slave nodes receive and adjust their clocks accordingly. This segmentation allows synchronization to occur only where needed (at master nodes sending sync frames) rather than requiring all nodes to oversample all messages, reducing overall resource consumption.
2Reliability
If digital clock synchronization is performed frequently to prevent message loss, then clock drift is compensated, but synchronization overhead increases and hardware requirements increase
Solution Approach 1:
The system implements periodic clock synchronization where master nodes send synchronization frames at predetermined intervals rather than continuously. This periodic action maintains clock synchronization across the network while significantly reducing the overhead compared to continuous synchronization, as the sync frames are sent only at necessary intervals based on the clock drift rate.
Solution Approach 2:
Synchronization frames act as intermediaries carrying timing information from master nodes to slave nodes. These frames serve as a mediator that transfers clock reference data without requiring direct hardware synchronization circuits between all node pairs, reducing hardware complexity while maintaining synchronization reliability.
3Reliability
If a customized operating system is used with digital clocks for synchronization, then message loss is prevented, but system complexity and implementation cost increase
Solution Approach 1:
Slave nodes automatically adjust their task activation clocks by processing received synchronization frames without requiring a customized operating system. The nodes self-service their synchronization needs by interpreting the sync frame data and adjusting their local clocks accordingly, maintaining message loss prevention while using standard operating systems.
Data Source
AI summary
A method for message loss prevention in a CAN system. The CAN system includes a plurality of distributed nodes, such as electronic control unit nodes that communicate with each other through a CAN bus. The distributed nodes are categorized into a first type node or a second type node. Further, each distributed node has its own task period which is the time taken by a node to complete a task allocated to it. First, a synchronization frequency is determined. Synchronization frames are sent to the second type node by the first type node at the synchronization frequency. Hereafter, task activation synchronization is performed on the second type node based on information included in the synchronization frames where the task activation synchronization is performed by adjusting the task period of the second type node.