How to debug freedom code

Hi,
I have a bare vcu118, and I have commented out the following code. But the uart has no output after downloading bitstream file:
//val fmc = Overlay(PCIeOverlayKey) (new PCIeVCU118FMCOverlay (_, _, ))
//val edge = Overlay(PCIeOverlayKey) (new PCIeVCU118EdgeOverlay (
, _, _))

So here I want to ask you how to debug the above problems for the freedom SoC development platform?

Thank you very much!