In reply to gennaro:
A few remarks.
(1) All tarnsaction level components like sequencers, scoreboardsa, coverage collectors do NOT need any virtual interface. These components do never knwo anything about tieming and clock cycles, reset etc.
(2) When you are doing the connections at the end of the build_phase this will work, but it is a bad coding style because we have the connect_phase to implement the connections.
With respect to the usage of the uvm_config_db commands:
(1) for the set in the toplevel module use as the first argument ‘null’. This is indicating the 2nd argument has to be considered as an absolute path
(2) for the get command commonly use as the first argument ‘this’. This indicates the 2nd argument has to be considered as an absolute path.
Following these rules covers 95% of the uvm_config_db usage.
A different 1st argument you need whan you want to pass data to sequences, because they do not belong to the testbench topology.
Hope this helps to fix your issues.