PSIC: Priority-Strict Multi-Core IRQ Processing

While processing external events, in the form of interrupt requests (IRQs), is a key concern of digital control systems, processing these events can be of different importance for a system’s functionality. Therefore, it is necessary, especially for real-time systems, to ensure that the handling of low-priority IRQs does not interfere with high-priority interrupt-service routines (ISRs) to prevent priority inversions. While prioritizing ISRs on single-core machines is a long-solved problem, priority-strict IRQ handling in multi-core systems is, as we will show, quite challenging with current interrupt controllers.With PSIC, we propose a hardware/software co-design that ensures the priority-strict execution of the top-m ISRs on an m-core machine at minimal interruption-induced overheads. We developed a drop-in replacement for an off-the-shelf interrupt controller that delivers IRQs in strict priority order while achieving low delivering delays at moderate hardware costs. Combined with a minimal IRQ software subsystem, which requires no inter-core synchronization, PSIC guarantees a priority-strict ISR execution on multiple cores.