The document discusses hardware-in-the-loop (HIL) simulation. (1) HIL simulation is a technique used in control system development that adds a real electronic control unit (ECU) component to a real-time simulation. (2) HIL simulation is used because directly connecting an ECU to a real plant for testing is not always possible due to time and complexity constraints in plant fabrication and controller design. (3) The HIL simulation procedure involves first simulating a model and PID controller software-only, then configuring the PID controller hardware-only, and finally testing the hardware PID controller on the simulated process using HIL simulation with both software and hardware.