time-limited licence problem

as your code shows no uart initialisation, i guess you have setup the uart with sopc builder to the desired speed, databits ....

have you checked with a scope that if you put a character to the uart, you can see it on the txd line ? maybe you need to uncheck hardware flow.

is your uart labeled uart_0 inside sopc builder ?

the qfp does not hold uart relevant informations except hardware related like fast input output registers, pin assignments.

so i agree you should basically check if your whole designs runs as expected.

also you can add signal tap and monitor the uart activities.

and the ide gives you the possability to debug your system and play with the uart by hand by alternating its registers.