Real-Time Software Pipelining for Multidomain Motion Controllers

Motion control systems require an isochronal real-time guarantee that each control task should periodically produce outputs with no jitters. However, it is difficult to build up such a tight isochronal system with a multicore architecture and a general-purpose operating system, because the inherent resource sharing principle leads to large jitters to the control tasks. This paper proposes a software pipelining framework for an EtherCAT-based motion controller that achieves a tight isochronal guarantee with that combination. The tight guarantee is possible by multicore partitioning and reservation-aware task phasing, which reduce resource contentions between the tasks on each stage of the pipeline. Through experiments, we show that the proposed pipelining framework gives a tight isochronal guarantee with high scalability in terms of the number of motion transactions. On a real 8-axis motion control platform with two processor cores dedicated to the pipeline and a slight modification of the Linux operating system, it achieves a maximum jitter of 10 μs for four motion transactions with a common period of 1.6 ms, whereas a priority-driven method gives a maximum jitter of a few hundreds of microsecond under the same condition.