CAN Queue Credit Arbitration for Fair Bus Access
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Solution Overview
Problem
Existing CAN systems face challenges in ensuring fair and efficient access to the CAN bus, particularly when multiple nodes with varying priority messages compete for transmission, leading to unequal waiting times and potential inefficiencies.
Innovation Solution
Implementing a CAN device with queues and associated queue credits that manage transmission based on predefined reference values and rank bits, allowing nodes to prioritize and balance the importance of messages for fair access to the CAN bus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If multiple CAN nodes with varying priority messages compete for transmission using traditional CAN protocols, then high priority messages can be transmitted quickly, but low priority messages experience unequal waiting times and potential transmission delays
Solution Approach 1:
The patent segments the transmission rights by dividing CAN frame transmission into multiple priority levels (rank bits). Each node is assigned a specific rank range, and frames are segmented into different priority categories based on their rank bits. This segmentation allows the system to handle multiple priority levels simultaneously, preventing low-priority messages from being indefinitely delayed by high-priority messages alone.
Solution Approach 2:
The patent changes the parameter of transmission priority by utilizing rank bits (predefined bits in each CAN frame) to represent different priority levels. By mapping rank bits to specific rank ranges and associating them with different transmission queues or priorities, the system dynamically adjusts transmission parameters based on message importance, ensuring both high-priority rapid transmission and fair treatment of low-priority messages.
2Device complexity
If traditional CAN protocols are used without queue credit mechanisms, then simple transmission control is maintained, but fair access to the CAN bus among multiple nodes is not ensured
Solution Approach 1:
The patent implements a queue credit mechanism that provides feedback control for CAN bus access. Each node maintains a queue credit value that is adjusted based on transmission outcomes and priority levels. When a node transmits a frame, its queue credit is updated, and this credit value feeds back into the arbitration process, determining future transmission opportunities. This feedback loop ensures fair access by preventing any single node from monopolizing the bus while maintaining simplicity through standardized credit management.
Solution Approach 2:
The patent introduces dynamic transmission control through queue credits that change based on node behavior and message priorities. Rather than static arbitration, the system dynamically adjusts which nodes can transmit by modifying queue credit values in real-time. This dynamic mechanism allows the system to adapt to varying traffic conditions while ensuring fair bus access, balancing complexity and operational ease.
3Productivity
If queue credits are used to manage transmission priorities, then fair and efficient bus access is achieved, but the system complexity increases with multiple queues and credit management
Solution Approach 1:
The patent applies universality by designing the queue credit mechanism to handle multiple priority levels and transmission scenarios through a single unified framework. The same queue credit structure manages both high-priority and low-priority messages, as well as arbitration between different nodes. This multi-functional approach improves communication efficiency across diverse message types while avoiding the need for separate complex management systems for each priority level or node.
Data Source
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AI summary
The present invention relates to a Controller Area Network, CAN, device (126, 127, 128), wherein the CAN device is configured to transmit and receive CAN frames (130, 134, 136, 138, 150, 152, 154, 202, 204), wherein the CAN device comprises a first queue (140) configured to including at least one first CAN frame (134, 136, 138), wherein a first queue credit (132) is associated with the first queue, wherein the CAN device is configured to, if the first queue credit is greater than a predefined first reference value, start to transmit at least one first CAN frame of the first queue, and wherein the CAN device is configured to, if the first queue credit is less than the predefined first reference value, prevent transmission of the at least one first CAN frame of the first queues. The present invention also relates to a CAN system (100) comprising a plurality of CAN devices and the CAN bus. Further, the present invention relates to a method (206) for the CAN device.