# Pastebin PW71MDtL
pdp7@x1:~/dev/fpga/nmigen$ python3 blinky.py simulate -c 20 -v blinky.vcd
Traceback (most recent call last):
  File "blinky.py", line 19, in <module>
    main(top, ports=(top.led))
  File "/home/pdp7/.local/lib/python3.7/site-packages/nmigen/cli.py", line 74, in main
    main_runner(parser, parser.parse_args(), *args, **kwargs)
  File "/home/pdp7/.local/lib/python3.7/site-packages/nmigen/cli.py", line 68, in main_runner
    with sim.write_vcd(vcd_file=args.vcd_file, gtkw_file=args.gtkw_file, traces=ports):
  File "/home/pdp7/.local/lib/python3.7/site-packages/nmigen/back/pysim.py", line 1117, in write_vcd
    vcd_file=vcd_file, gtkw_file=gtkw_file, traces=traces)
  File "/home/pdp7/.local/lib/python3.7/site-packages/nmigen/back/pysim.py", line 95, in __init__
    if trace not in signal_names:
  File "/usr/lib/python3.7/_collections_abc.py", line 666, in __contains__
    self[key]
  File "/home/pdp7/.local/lib/python3.7/site-packages/nmigen/hdl/ast.py", line 1385, in __getitem__
    key = None if key is None else self._map_key(key)
  File "/home/pdp7/.local/lib/python3.7/site-packages/nmigen/hdl/ast.py", line 1575, in __init__
    raise TypeError("Object {!r} is not an nMigen signal".format(signal))
TypeError: Object (slice (sig led) 0:1) is not an nMigen signal