@Anshumaan Kumar Yadav: Simulating the whole Caravel chip from the top level is probably easier than trying to instantiate gpiov2 pads into your testbench. The gpiov2 pads are very complicated and difficult to set up correctly. On Caravel, there is a complicated control interface between the user project and the GPIO pads. I'm not sure what you're trying to accomplish by placing the pads directly into a simulation.