Dynamic Margin Time Arbitration for CAN Message Delivery
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Solution Overview
Problem
In vehicle communication systems using the CAN standard, message transmissions with lower priority are often hindered continuously due to higher-priority messages, as priority is statically determined and not dynamically adjusted based on message urgency.
Innovation Solution
A communication device and method that calculates a 'margin time' for each message, attaching this information to the message, and prioritizes transmissions based on the margin time during arbitration, ensuring messages with shorter margin times are transmitted first.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If static priority based on CAN ID is used for message arbitration, then the arbitration process is simple and fast, but low-priority messages are continuously hindered by high-priority messages
Solution Approach 1:
The patent applies dynamics by transitioning from static CAN ID-based priority to dynamic margin time-based priority. The margin time is calculated based on the deadline time and current time, allowing priority to change dynamically according to message urgency. This resolves the contradiction by enabling both fast arbitration (through simple margin time comparison) and reliable message delivery (by prioritizing urgent messages with shorter margin times).
Solution Approach 2:
The patent changes the arbitration parameter from fixed CAN ID to variable margin time. The margin time is calculated as (deadline time - current time) and attached to each message. During arbitration, messages are prioritized based on their margin time rather than static ID, allowing the system to adapt priority dynamically while maintaining simple arbitration logic. This parameter change enables both efficiency and reliability.
2Reliability
If margin time calculation and attachment to messages is implemented, then message priority reflects actual urgency, but system complexity increases
Solution Approach 1:
The patent changes the arbitration parameter from fixed CAN ID to variable margin time. The margin time is calculated as (deadline time - current time) and attached to each message. During arbitration, messages are prioritized based on their margin time rather than static ID, allowing the system to adapt priority dynamically while maintaining simple arbitration logic. This parameter change enables both efficiency and reliability.
Solution Approach 2:
The arbitration unit performs self-service by automatically calculating and comparing margin times without external intervention. Each message carries its own margin time information, and the arbitration unit simply compares these values to determine priority, eliminating the need for complex external priority management systems while ensuring reliable message delivery based on actual urgency.
3Reliability
If dynamic priority based on margin time is used, then low-priority messages can be transmitted timely, but arbitration processing time increases
Solution Approach 1:
The patent applies preliminary action by calculating the margin time in advance before arbitration occurs. The margin time is computed as (deadline time - current time) and attached to the message at the time of transmission request. This preliminary calculation eliminates the need for complex real-time priority determination during arbitration, allowing the arbitration unit to simply compare pre-calculated margin times and make quick decisions, thus maintaining fast arbitration while ensuring reliable message delivery.
Data Source
AI summary
A communication device that can prevent the transmission of a message from being continuously hindered over a long period of time, a communication system and a message arbitration method are provided. The communication device transmits and receives a message to and from another device connected to a common communication line which comprises a calculation unit that calculates as to a message to be transmitted a margin time before a time when a transmission of the message is completed; a transmission unit that transmits the message to which information related to the margin time calculated by the calculation unit is attached; and an arbitration unit that performs arbitration based on the information attached to the message when simultaneous message transmissions to the communication line occur, and as to multiple of messages simultaneously transmitted to the communication line, the arbitration unit performs arbitration in such a manner as to prioritize a message with a shorter margin time.