Porting SLOTH system to FreeRTOS running on ARM Cortex-M3

Traditionally, operating system (OSes) suffers from a bifid priority space dictated by the co-existence of threads managed by kernel scheduler and asynchronous interrupt handlers scheduled by hardware. On real-time systems, where reliability and determinism plays a critical role, this approach presents a noteworthy lack, as any interrupt handler can interrupt an execution thread, regardless of its priority. This paper presents the implementation of an unified priority space approach (SLOTH), handling each thread as an interrupt. A light-weight version of FreeRTOS was internally redesigned, to replace the software scheduler by a hardware one, which exploits a Commercial Off-The-Shelf (COTS) hardware interrupt controller, provided by ARM Cortex-M3. The results showed that our implementation solves the priority inversion problem, and simultaneously improves the system performance, reduces the memory footprint and simplifies maintainability.