Compounded Real-Time Operating Systems for Rich Real-Time Applications

In embedded systems, the emergence of rich applications requires real-time operating systems (RTOSs) that provide rich features. This paper describes compounded RTOSs (cRTOSs) that provide the rich features of a general-purpose operating system (GPOS) in a traditional RTOS (tRTOS). A cRTOS partitions a physical machine with a hypervisor and executes the GPOS and tRTOS in parallel. In the cRTOS, a rich RT application executes in the tRTOS, and accesses not only the RT features of the tRTOS via local system calls but also the rich features of the GPOS via remote system calls and signals. The remote system calls and signals are built on top of remote procedure calls to a service program in the GPOS. Contrary to existing solutions such as PREEMPT_RT or Xenomai, the cRTOS does not require modification of the GPOS kernel and allows the use of a wide range of tRTOSs. This paper evaluates the proposed method by implementing three cRTOSs on Raspberry Pi 4B. They use Jailhouse as the hypervisor, Linux as the GPOS, and NuttX or FreeRTOS as the tRTOS. This paper also evaluates their usability by implementing three rich RT applications on the three cRTOSs. This paper compared the RT performance of the implemented cRTOSs to PREEMPT_RT and Xenomai using timing accuracy and interrupt latency benchmarks. The results show that the cRTOSs delivered a better RT performance with a minimum of 5 microsecond jitter and a well-bounded lower maximum latency in these two benchmarks than the other RTOSs.