Taming Linux Jitter: Achieving Sub-50µs Cycle Times with PREEMPT_RT and Xenomai

Tue, 21 Jul 2026 00:00:00 +0000

1. The Challenge: Soft PLC on a $30 SoC

Tainuo’s next-generation motion controller needed to run a soft-PLC runtime doing 20 kHz closed-loop PID control on six servo axes simultaneously. The target hardware: a $30 Allwinner A40i quad-core Cortex-A7. No FPGA, no dedicated DSP — just plain ARM cores running Linux.

The problem was obvious: standard Linux, even with SCHED_FIFO, routinely exhibits 200–500µs scheduling jitter on this class of hardware. For a 20 kHz control loop (50µs period), that’s a non-starter. Missing the deadline means a phase error that accumulates and destabilizes the mechanical system.

Xenomai on TiJet

Taming Linux Jitter: Achieving Sub-50µs Cycle Times with PREEMPT_RT and Xenomai

1. The Challenge: Soft PLC on a $30 SoC