Hybrid real-time operating systems: deployment of critical FreeRTOS features on FPGA

Performance and determinism are two critical metrics in most embedded systems with real-time requirements. Owing to the complexity of current embedded systems, along with increased application demands, real-time operating systems (RTOSs) have become a de facto solution providing specific services to the system tasks. However, this extra layer, which abstracts the hardware from the software, makes it harder for a system to achieve good performance and determinism. To ease the impact of a RTOS in the system, RTOS run-time services are offloaded to the hardware layer. This paper presents a hybrid RTOS implementation, where several critical RTOS services were migrated from software to hardware, improving system latency and predictability. Special focus was given to the RTOS scheduler and to the mutexes handling subsystem. The developed hardware accelerators were synthesised on a field-programmable gate array (FPGA), exploiting the point-to-point fast simplex link (FSL) bus to interconnect to the Xilinx Microbaze soft-core processor. Our approach shows that hybrid RTOS has a better performance and predictability when compared to its software-only version.