Subscriber Station Scheduling Unit for Deterministic Serial Bus Access
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Solution Overview
Problem
Current CAN-based bus systems cannot guarantee 100% deterministic bus access, which is essential for real-time critical applications, as they rely on arbitration methods that may lead to collisions and unpredictable message transmission times.
Innovation Solution
A subscriber station for a serial bus system equipped with a communication control device, a transmitting/receiving device, and a scheduling unit that allows deterministic scheduling, ensuring each subscriber station has a guaranteed time slot for transmission, enabling deterministic bus access and real-time critical applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If arbitration method (CSMA/CR) is used for bus access, then system complexity is reduced and ease of operation is improved, but deterministic bus access cannot be guaranteed and message transmission time becomes unpredictable
Solution Approach 1:
The system dynamically switches between two communication modes: a first mode using CSMA/CR arbitration for non-critical messages, and a second mode using time-triggered deterministic scheduling for critical messages. This dynamic adaptation allows the system to optimize between ease of operation and deterministic reliability based on message priority requirements.
Solution Approach 2:
The bus communication is segmented into different priority levels and time slots. High-priority deterministic messages are allocated specific time slots within communication cycles, while lower-priority messages use arbitration-based access. This segmentation allows simultaneous operation of both arbitration and deterministic scheduling without mutual interference.
2Reliability
If deterministic scheduling is implemented to guarantee 100% deterministic bus access, then reliability for real-time critical applications is improved, but device complexity increases due to additional scheduling unit and time slot management
Solution Approach 1:
The communication control device performs multiple functions: it handles both CSMA/CR arbitration for standard messages and deterministic time-triggered scheduling for critical messages. This multi-functionality consolidates what could be separate systems into a single universal controller, reducing overall system complexity while maintaining deterministic capabilities.
Solution Approach 2:
The scheduling unit automatically manages time slot allocation and cycle timing without requiring external coordination. Each subscriber station independently tracks its assigned time slots and transmits deterministic messages autonomously, eliminating the need for complex centralized scheduling control and reducing device complexity.
3Reliability
If time slot allocation is used for deterministic access, then communication bandwidth guarantee is improved, but loss of time increases due to fixed cycle structure and waiting periods
Solution Approach 1:
The system allows dynamic adjustment of communication cycle parameters including cycle duration, time slot lengths, and slot allocation ratios. By optimizing these parameters based on actual traffic requirements, the system minimizes waiting time while maintaining guaranteed bandwidth for deterministic messages, resolving the contradiction between bandwidth guarantee and time efficiency.
Data Source
AI summary
A subscriber station for a serial bus system. The subscriber station has a communication control device for controlling a communication of the subscriber station with at least one other subscriber station, a transmitting/receiving device for transmitting a transmission signal generated by the communication control device, and a scheduling unit for scheduling a temporal access of the subscriber station to the bus in at least one time slot of a cycle of temporally consecutive time slots. At least one time slot is provided in a cycle for each subscriber station of the bus for transmitting its transmission signal and the cycle repeats cyclically. The scheduling unit determines, together with the other subscriber stations of the bus in the operation of the bus system using a priority of the transmission signal, which time slot of the cycle the transmitting/receiving device may use for transmitting the transmission signal on the bus.