Case study: Interrupt-less servo motor controls for pneumatic pump in safety critical devices

Interrupts are often used in safety critical control software, however, a system based on interrupts is difficult to analyze, which increases cost and complexity of software quality assurance, because the behavior may vary depending on the order in which interrupts are detected by the sensors. In the previous work on servo motor controls, an interrupt-driven architecture is successfully converted to the interrupt-less architecture by maintaining time stamps of sensor events. In this paper, interrupt-less servo motor controls for pneumatic pump system in medical devices are evaluated and analyzed in terms of behavior correctness as well as the predictability of the system. Experimental results show negligible differences on the main control variable of servo motor compared to the interrupt-driven controls while it provides better predictability by getting rid of interrupts except an internal timer for periodic handling of time stamps by sensor events including motor, pump pusher plate, and buttons in the user interface.