The best of both: High-performance and deterministic real-time executive by application-specific multi-core SoCs

Embedded multi-core processors improve performance significantly and are desirable in many application-fields. This in particular includes safety-critical real-time systems, which typically require a deterministic temporal behavior. However, even tasks without dependencies running on different cores can interfere due to, sometimes hidden, shared hardware resources, such as common memories or buses. Consequently, only a pessimistic assumption of the worst-case execution time (WCET) that incorporates interference can be given. Hence, the aspired performance gain fizzles out in the poor temporal analyzability. Based on the fact that in safety-critical systems all tasks and their dependencies are known at compile-time, this paper presents an approach to generate application-specific, deterministic multi-core processor architectures for these systems. Thereby safety-critical tasks are executed on dedicated Deterministic Execution Units (DEUs) including lightweight, deterministic processor cores, bus systems, memories and peripherals. The remaining soft real-time tasks are executed on a general purpose multi-core processor that offers performance over determinism. Consequently, timing analysis for hard real-time tasks is significantly simplified, since interferences caused by shared resources and scheduling are effectively eliminated. To show the benefits of our approach, an application-specific architecture for a flight controller was generated and compared to an ARM Cortex-A9 dual-core as reference. Overall, we were able to significantly improve temporal properties of safety-critical tasks while preserving the overall performance for soft real-time tasks.