Verifying Simulink generated C code

I generated embedded C code for the plant in the following MATLAB Simulink model:

To verify that the generated code behaves the same as the Simulink model, I could save the controller outputs to a file, create a C project with a main() function to read those outputs, and feed them to the plant C code at each time step—essentially converting a closed-loop simulation into an open-loop one. This approach would work if I use a single-step numerical integrator/solver like ode1 (Euler method). However, I usually prefer ode4 (Runge-Kutta 4) due to its better accuracy with less computation. Despite RK4 having 4 intermediate computations, it has a global error of O(h^4) and Euler O(h). If RK4 uses a step size of h, Euler would need h^4 to achieve similar accuracy. So, in total Euler would require more function evaluations than RK4—specifically, (1/h^3)/4 times more. For example, if hRK4 = 0.1, Euler would need 250x more computations.

Unfortunately, RK4 is a multi-step method with minor step sizes. Since the Simulink model saves controller outputs only at major steps, reading them from a file to drive the plant might result in divergent behavior—especially if the system has high-frequency dynamics—because controller outputs could differ at minor steps, while reading from the file only accounts for major step outputs.

You can only fully verify the system by integrating the C code into your embedded setup, which generates controller outputs based on real time plant-sensor data. Since testing on an embedded system takes time, to catch issues such as uninitialized variables in the plant code, you can create a C project, build and run your plant model with constant controller inputs. If it compiles and runs without NaN values, you can proceed to the embedded testing phase.

If you want to be more rigorous, you could save the plant outputs together with the controller outputs. In your C project, you read the controller output, feed it to the plant, run it for only one time step, read the Simulink plant output for that time instance from a file, and compare it with the C code plant output. Even this comparison is not perfect and only works for the first time step because Simulink integrator block outputs depend on the system state in the previous time step. To check the whole time span, you also have to save the system state and initialize the system with the correct state at each time step.