[Sim] Error with fsm delayed_enter method

[kamejoko80]

Hello,

When I trying to simulate the FSM behavior then I found the below issue:

In my code:

        fsm.act("STATE_1",
            If(self.trigger_2,
                NextState("STATE_2"),
            )
        )
        # Delay 4 clock circles when switching from STATE_1 to STATE_2
        # However this methode is not able to simulate, why?
        fsm.delayed_enter("STATE_1", "STATE_2", 4)

        fsm.act("STATE_2",
        )

I got the following error message from the console:

Traceback (most recent call last):
  File "/home/Workspace/litex/migen/migen/sim/core.py", line 414, in run_simulation
    s.run()
  File "/home/Workspace/litex/migen/migen/sim/core.py", line 406, in run
    self._commit_and_comb_propagate()
  File "/home/Workspace/litex/migen/migen/sim/core.py", line 338, in _commit_and_comb_propagate
    self.vcd.set(signal, self.evaluator.signal_values[signal])
  File "/home/Workspace/litex/migen/migen/sim/vcd.py", line 66, in set
    self._write_value(self.buffer_file, signal, value)
  File "/home/Workspace/litex/migen/migen/sim/vcd.py", line 60, in _write_value
    self._write_enum_value(self.buffer_file, signal, value)
  File "/home/Workspace/litex/migen/migen/sim/vcd.py", line 53, in _write_enum_value
    for c in signal._enumeration[value].encode():
AttributeError: 'AnonymousState' object has no attribute 'encode'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/Workspace/litex/litex-soc-builder/custom_ipcores/sim.py", line 162, in <module>
    run_simulation(dut, FSM_SIM_TB(dut), clocks={"sys": 10}, vcd_name="FSM_SIM.vcd")
  File "/home/Workspace/litex/migen/migen/sim/core.py", line 413, in run_simulation
    with Simulator(*args, **kwargs) as s:
  File "/home/Workspace/litex/migen/migen/sim/core.py", line 323, in __exit__
    self.close()
  File "/home/Workspace/litex/migen/migen/sim/core.py", line 326, in close
    self.vcd.close()
  File "/home/Workspace/litex/migen/migen/sim/vcd.py", line 82, in close
    size = max([len(v) for v in signal._enumeration.values()])*8
  File "/home/Workspace/litex/migen/migen/sim/vcd.py", line 82, in <listcomp>
    size = max([len(v) for v in signal._enumeration.values()])*8
TypeError: object of type 'AnonymousState' has no len()

``
I've tried to build the project and saw that my code is synthesizable, something wrong in vcd.py.