CAN Controller Arbitration Delay for Fair Best-Effort Traffic
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Solution Overview
Problem
Existing CAN protocols struggle to efficiently handle both event-triggered and best effort traffic without impacting bus utilization, leading to unpredictable latencies and unfair behavior, particularly in heavy traffic conditions where strict priority is required.
Innovation Solution
A CAN communication controller that transmits first and second types of frames, where the first type is for event-triggered communication and the second type is for best effort traffic, with mechanisms to delay arbitration of best effort frames using a finite state machine to manage bandwidth distribution, ensuring minimal impact on event-triggered communication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If best effort traffic is transmitted on CAN bus using standard CAN protocols, then bandwidth utilization increases, but event-triggered communication latency becomes unpredictable and strict priority is lost
Solution Approach 1:
The patent segments the CAN bus communication into two distinct types: event-triggered frames with strict priority and best-effort frames with relaxed priority. This is achieved by creating separate transmission queues and arbitration mechanisms for each traffic type, allowing best-effort traffic to be transmitted without interfering with the priority guarantees of event-triggered communication.
Solution Approach 2:
The patent introduces an intermediary mechanism in the form of a gateway or protocol adapter that mediates between best-effort traffic sources and the CAN bus. This intermediary translates best-effort traffic into appropriate CAN frames, manages arbitration delays, and ensures that such traffic does not compromise the timing requirements of event-triggered communication.
2Reliability
If bus utilization is limited to 70% to ensure bounded latency, then event-triggered communication reliability is maintained, but overall network productivity is reduced
Solution Approach 1:
The patent applies local quality by providing different service levels to different traffic types on the same physical medium. Event-triggered frames receive high-priority treatment with guaranteed bandwidth and bounded latency, while best-effort frames are transmitted in the remaining capacity without strict timing requirements. This allows the network to operate at higher overall utilization while maintaining reliability for critical communications.
3Productivity
If multiple nodes transmit simultaneously on CAN bus, then communication efficiency improves, but arbitration conflicts increase and fairness deteriorates
Solution Approach 1:
The patent implements periodic action through round-robin arbitration for best-effort traffic. After event-triggered frames are transmitted, the system periodically allows best-effort nodes to access the bus in a rotating sequence. This periodic access pattern ensures fair distribution of bandwidth among multiple best-effort nodes while maintaining high communication efficiency through coordinated simultaneous transmissions.
Data Source
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AI summary
A CAN communication controller (5) and a method of operating a CAN communication controller are disclosed. The CAN communication controller is for transmitting first and second types of frames (7, 8) wherein the first type of frame (7) is used to transmit event-triggered communication data and the second type of frame (8) is used to transmit best effort traffic data, the CAN communication controller configured, in response to transmitting a frame of the second type having a given identifier (9), to delay arbitration of a following frame of the second type having the given identifier, and not to delay arbitration of a frame of the first type.