docs: def _write_config(self, memory):
          """Write the configuration for this probe to memory."""
          memory.seek(0)
          memory.write(struct.pack("<II",
                                   # sim_length
                                   self._simulator.length,
                                   # input_key
                                   self._input.routing_key
                                   if self._input is not None
                                   else 0xFFFFFFFF))