Sender Buffer Traffic Shaping for CAN Message Loss Prevention
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Solution Overview
Problem
In controller area network (CAN) systems, messages can be lost due to contention, delays, and finite buffer sizes, as there is no central computer to ensure message integrity and prevent overwrite, leading to potential loss of data during transmission between nodes.
Innovation Solution
Implementing a sender buffer with a timer function that stores messages and manages their transmission based on the availability of the bus controller and a predetermined time interval after successful transmission of previous messages, thereby reducing message loss through a distributed embedded real-time CAN system with traffic shaping to manage message transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If messages are transmitted immediately when ready without buffering, then transmission speed is improved, but message loss occurs due to bus controller unavailability and contention
Solution Approach 1:
The sender buffer pre-stores messages before the bus controller is available, so that when the bus controller becomes available, messages can be transmitted immediately without loss. This preliminary buffering action resolves the contradiction by preparing messages in advance rather than waiting for bus availability.
Solution Approach 2:
The sender buffer acts as an intermediary between the message generator and the bus controller. It decouples the message generation process from the transmission process, allowing messages to be stored temporarily and transmitted when the bus controller is available, thus preventing message loss while maintaining transmission efficiency.
2Reliability
If a sender buffer is implemented to store messages, then message loss is reduced, but device complexity increases
Solution Approach 1:
The buffering function is segmented into a dedicated sender buffer component within the ECU, separate from the bus controller and application components. This segmentation allows the buffer to be a simple first-in-first-out structure without complex control logic, reducing overall system complexity while maintaining reliability.
Solution Approach 2:
The sender buffer operates autonomously using a simple first-in-first-out mechanism with automatic enqueue and dequeue operations triggered by bus controller availability. This self-service approach eliminates the need for complex centralized control logic, reducing device complexity while ensuring reliable message storage and transmission.
3Reliability
If traffic shaping with predetermined time intervals is used, then message contention is reduced, but transmission delay increases
Solution Approach 1:
The traffic shaping module implements periodic transmission attempts at predetermined time intervals after successful message transmission. This periodic action prevents bus controller overload by spacing out transmission requests, reducing contention and improving reliability while maintaining acceptable transmission delays through reasonable interval selection.
Solution Approach 2:
The traffic shaping interval is dynamically adjusted based on bus controller availability and system load conditions. When the bus controller is frequently available, intervals can be shorter; when overloaded, intervals extend automatically. This dynamic adaptation optimizes the balance between reducing contention and minimizing transmission delays.
Data Source
AI summary
A vehicular distributed embedded real-time controller area network system includes ECUs that function in an event-triggered mode to initiate a transmission of the message to the communication bus. Each ECU includes a sender buffer for storing the generated message. A bus controller interfaces with the ECUs and manages the transfer of messages to and from the communication bus. The transfer of messages onto the communication bus is executed by the controller area network controller on an interrupt basis. The bus controller being unavailable to receive a message from the ECU when a previous message stored within a memory of the bus controller is awaiting transmission on the communication bus. The bus controller is available to receive a message from the ECU when the memory is empty. The sender buffer stores messages received from the electronic control unit when the bus controller is unavailable. The ECU further includes a traffic shaping module for selectably delaying a transfer of messages to the bus controller.