SmallRTOS: Microcontroller-based embedded multitasking

In a multi-tasking system, numerous tasks require CPU time, and since there is only one CPU, some form of organization and coordination is needed so each task has the CPU time it needs. In practice, each task takes a very brief amount of time, so it seems as if all the tasks are executing in parallel and simultaneously. In the case of excessive complexity applications, which usually run in hard real time constraints, the use of a real time operating system (RTOS) is strongly required. In this paper, a tiny and reliable RTOS was implemented for PIC18F family of microcontroller. This operating system, which is called SmallRTOS, is based on Round-Robin scheduler. The used system tick is based on a variable time-sliced scheduling that has a direct effect on CPU load, context switching and process waiting time.