In automatic systems used in the control and monitoring of industrial processes, fieldbuses with specific real-time requirements are used. Often, the sensors are connected to these fieldbuses through embedded systems, which also have real-time features specific to the industrial environment in which it operates. The embedded operating systems are very important in the design and development of embedded systems. A distinct class of these operating systems is real-time operating systems (RTOSs) that can be used to develop embedded systems, which have hard and/or soft real-time requirements on small microcontrollers (MCUs). RTOSs offer the basic support for developing embedded systems with applicability in a wide range of fields such as data acquisition, internet of things, data compression, pattern recognition, diversity, similarity, symmetry, and so on. The RTOSs provide basic services for multitasking applications with deterministic behavior on MCUs. The services provided by the RTOSs are task management and inter-task synchronization and communication. The selection of the RTOS is very important in the development of the embedded system with real-time requirements and it must be based on the latency in the handling of the critical operations triggered by internal or external events, predictability/determinism in the execution of the RTOS primitives, license costs, and memory footprint. In this paper, we measured and compared the timing performance for synchronization throughout an event, semaphore, and mailbox for the following RTOSs: FreeRTOS 9.0.0, FreeRTOS 10.2.0, rt-thread, Keil RTX, uC/OS-II, and uC/OS-III. For the experimental tests, we developed test applications for two MCUs: ARM Cortex™-M4 and ARM Cortex™-M0+ based MCUs.
Timing Comparison of the Real-Time Operating Systems for Small Microcontrollers