%Error: t/t_udp_sequential_bad.v:8:8: For combinational UDP, the output must not be a 'reg' data type
                                    : ... note: In instance 'top'
    8 | output dout;
      |        ^~~~
        ... See the manual at https://verilator.org/verilator_doc.html?v=latest for more assistance.
%Error: Exiting due to