ProcessorintheLoop

Processor-in-the-loop (PIL) is an embedded systems testing method in which the control software intended for a target processor is executed on the actual hardware while the plant or environment model runs in real time on a simulator or host computer. The target processor exchanges sensor and actuator signals with the plant model through real-time I/O, allowing validation of software-hardware interaction, timing, and fault handling prior to full hardware deployment.

PIL sits between software-in-the-loop (SIL) and hardware-in-the-loop (HIL). Unlike SIL, PIL runs the compiled executable on the real processor, not a workstation. Unlike full HIL, the plant is a simulated model rather than a physical system, reducing hardware needs while preserving realistic processor behavior such as timing and interrupts.

Typical workflow: port or develop the control algorithm for the target, build a binary, set up a real-time plant model and interface hardware I/O, and run the loop in real time. Data from the target is logged and compared to reference results or to SIL/HIL baselines. Debugging and profiling focus on timing, memory use, and interrupt handling.

Applications include automotive ECUs, aerospace control systems, robotics, and industrial automation. PIL helps verify integration and timing early, reduces risk, and can speed up hardware verification when full physical prototypes are limited.

Challenges include ensuring deterministic timing and low jitter in the host-target loop, managing latency in I/O, complicated setup, and tooling compatibility. For safety-critical systems, PIL is typically part of a broader validation strategy that may also involve SIL and HIL and compliance with standards such as ISO 26262 or DO-178C.