Multi-core processors are gaining increasing importance in safety-relevant embedded realtime systems, where temporal guarantees must be ensured despite the sharing of on-chip resources such as processor cores and networks-on-chip (NoC). At the same time, many applications comprise workloads with different timing models including time triggered and event-triggered communication.
The first contribution is a scheduling model based on Mixed Integer Linear Programming(MILP) supporting the allocation of computational jobs to processing cores as well as the scheduling of messages and the selection of paths on NoC. The model supports dependencies between computational jobs and it combines both time-triggered and event-triggered messages. Phase alignment of time-triggered messages is performed while avoiding collisions between time-triggered messages and satisfying bandwidth constraints for event-triggered messages. Example scenarios are solved optimally using the IBM CPLEX optimizer yielding minimal computational and communication latencies.
Real-time communication and reliability are two important requirements in the development of safety-critical embedded systems, which benefit from the inherent fault isolation and temporal predictability of time-triggered networks. These systems depend on redundant communication schedules that contain global time-based information of message transmissions with conflict-free paths through the switches. In these systems, the use of redundancy to handle communication errors requires the preallocation of communication resources. The second contribution introduces a novel scheduler for redundant time-triggered networks that assigns messages to redundant paths. The scheduler considers the link reliability along with physical and logical models and produces a schedule where each message is assigned to two different paths along the switches. We also discuss and validate the approach with results from a prototype implementation.
SoS consist of complex interconnections of large numbers of networked embedded systems that are characterized by operational and managerial independence of constituent systems, geographical separation, and emergent behavior in a constantly changing environment. The support for real-time communication is crucial for many SoS application areas such as medical, business, and military systems. The third contribution is a conceptual model and a scheduling algorithm for supporting real-time requirements in SoS. The search for a feasible schedule is computed incrementally upon the introduction of new applications in the SoS. The distributed computation of the schedule using the different constituent systems considers the lack of global knowledge and control in the SoS, while also reducing the overall scheduling time. Concurrent scheduling activities are supported to deal with the uncoordinated and possibly simultaneous introduction of multiple applications.
The dissertation introduces also a simulation framework with real-time support of SoS that supports high-level scheduling as well as low-level scheduling for each constituent system. A time-triggered Ethernet (TTEthernet) simulation framework was extended by adding a scheduler layer to perform incremental scheduling among Constituent System Managers (CSMs). The simulation framework enabled the evaluation of the proposed algorithms in terms of schedulability, run-time, and worst-case latency for time-triggered and rate-constrained messages.