Hi Cristina,
If I am understanding it correctly, you are using a 4 kHz carrier frequency to generate the pwm. In this case, I can see you are using the GPIO digital input sample time of 0.1, which is very high for logging the PWM samples. Try to reduce the GPIO sample time to 1e-5 and log the signal in Simulink Data Inspector to visualize the signal. Ensure the GPIO block is configured correctly for the corresponding pin you are shorting.
You can find more information about GPIO in the following documentation.
Hope this helps to resolve the issue.
