Traceback (most recent call last):
  File "tst_wave.py", line 6, in <module>
    with Simulator( dut, vcd_file = open( 'wave.vcd', 'w' ) ) as sim:
  File "/home/ericb/.local/lib/python3.7/site-packages/nmigen/back/pysim.py", line 920, in __init__
    self._state.start_waveform(_VCDWaveformWriter(self._signal_names, **kwargs))
  File "/home/ericb/.local/lib/python3.7/site-packages/nmigen/back/pysim.py", line 120, in __init__
    var_type=var_type, size=var_size, init=var_init)
  File "/home/ericb/.local/lib/python3.7/site-packages/vcd/writer.py", line 196, in register_var
    var.format_value(init, check=True)
  File "/home/ericb/.local/lib/python3.7/site-packages/vcd/writer.py", line 629, in format_value
    value_str = self._format_value(value, self.size, check)
  File "/home/ericb/.local/lib/python3.7/site-packages/vcd/writer.py", line 647, in _format_value
    raise ValueError('Invalid vector value ({})'.format(value))
ValueError: Invalid vector value (129)