Preemption-resistant control on a non-real-time operating system

We propose an architecture for implementing discrete-time control algorithms on a non-real-time operating system so that sensing and actuation occur at precise times, even if the OS preempts the control task. The architecture has the controller perform its computation on one processor and its sensing/actuation on a separate microcontroller. The controller sends arrays of future time-stamped actuator commands to the microcontroller, thereby allowing actuation to continue if preemption occurs. We use this architecture to drive a DC motor with a Beaglebone Black single-board computer, with the controller running on Linux and the I/O performed on a subsidiary microcontroller within the Beaglebone. This scheme achieves a timing accuracy of 40 μs. We demonstrate that this configuration improves a PID controller’s performance in the presence of OS preemption, even when the preemption persists across several sampling periods. In effect, this provides a mechanism to make a controller resistant to OS preemption.