# Scheduling the Exchange of Context Information for Time-Triggered Adaptive Systems
## 1 Introduction
The interactive consistency protocol introduced in [13; 14] enables the periodic exchange of context events within the time-triggered paradigm, ensuring synchronized decision-making. Furthermore, the approach allows the context exchange period to be tuned according to the timing requirements of the application, preserving both predictability and safety. This work builds on the key idea that adaptation must be deterministic in time-triggered off-chip multi-processor system-on-chip (MPSoC) platforms. In such systems, context event exchanges can be anticipated and optimized in advance. Since the context events are known and temporally ordered at design time, the metascheduler can precompute all valid combinations of event occurrences and their corresponding schedules, which are represented in a multi-schedule graph (MG). Each node in the MG corresponds to a specific context event pattern, with its schedule derived from the state of its predecessor. The critical insight here is that the need for context information exchange is not periodic but conditional. It depends on whether a particular context event brings about a behavioral change that affects downstream components. As a result, communication of context information is triggered only at specific transitions in the MG, namely when a successor schedule differs from its predecessor in a way that requires informing particular end systems. In contrast to previous methods that broadcast context messages periodically or to all nodes indiscriminately, our approach integrates the context exchange problem with the scheduling optimization problem. For each schedule node, only the affected end systems--those that experience task or message changes compared to their predecessor--are selected as recipients of the context information. This selective strategy significantly reduces communication overhead while ensuring deterministic system behavior. In essence, the scheduling process becomes context-aware and communication-efficient. The scheduler determines the timing of tasks and messages and when and where context messages need to be sent. This results in \"design-time clairvoyance,\" allowing the system to plan adaptation steps with minimal runtime overhead proactively. This study introduces an algorithm designed to reduce communication overhead in the context of metascheduling for system adaptation. The key contributions of this work include:  
* Conceptualization of context information with its respective timing requirements. * Development of a synthesis algorithm for the context exchange scheduling problem. The algorithm is based on selective communication to nodes that need the information. The selective communication is designed based on upcoming decision points, and the communication of context information is temporarily aligned with decision-making on schedule changes. This contribution maximizes the impact of adaptation while minimizing the communication cost. * Evaluation of the improvements of the proposed synthesis algorithm by benchmarking against the current practice. The remainder of this paper is organized as follows: Section 2 reviews related work in metascheduling, context-aware adaptation, and communication optimization in time-triggered systems. Section 3 introduces the foundations and motivations for adaptive time-triggered systems. Section 4 defines the context exchange scheduling problem and presents the proposed synthesis algorithm, including the selective communication strategy aligned with decision points. Section 5 presents experimental results and a comparative analysis demonstrating the effectiveness of the proposed approach in reducing communication overhead and improving adaptation efficiency. Finally, Section 6 concludes the paper.