@internal<EOL>def _simUnitVcd(simModel, stimulFunctions, outputFile, until):
sim = HdlSimulator()<EOL>sim.config = VcdHdlSimConfig(outputFile)<EOL>sim.simUnit(simModel, until=until, extraProcesses=stimulFunctions)<EOL>return sim<EOL>
:param unit: interface level unit to simulate
:param stimulFunctions: iterable of function(env)
    (simpy environment) which are driving the simulation
:param outputFile: file where vcd will be dumped
:param time: endtime of simulation, time units are defined in HdlSimulator
:return: hdl simulator object