Abstract: A method for providing a real-time testing of a control system or a part thereof to control a process or a part thereof of a real world system. The method includes connecting the control system or the part thereof to a real-time simulator to simulate the real world system, providing a simulation of the real world system in real-time by applying a modified variable step-size solver, and monitoring a real-time performance of the real-time simulator and adapting step-sizes used for the modified variable step-size solver to run the simulation by comparing a time used by the modified variable step-size solver to simulate the real world system with a real-time clock, setting a maximum step-size of the modified variable step-size solver based on a sample rate of the control system, and forcing the modified variable step-size solver to return a simulation result when demanded by the control system.