part7b of tutorial has no result returned back

[jsncepu]

Hi. I have build the project sucessfully by following the tutorial part7a. However, after I copied the files to pynq boards and executed commands in part7b, I got nothing. It seems that the command:
y_hw, latency, throughput = nn.predict(X_test, profile=True)
never terminates.
So how can I fix the problem? Could anyone give me some advices? Thanks a lot!