System status (:py:class:`SystemStatus`).

        The status has a ``state`` property with one of the following values:

        * ``UNINIT``: Uninitialized system, state is unknown.
        * ``BOOT``: System is booting up.
        * ``CALIBRATING``: System is calibrating and not flight-ready.
        * ``STANDBY``: System is grounded and on standby. It can be launched any time.
        * ``ACTIVE``: System is active and might be already airborne. Motors are engaged.
        * ``CRITICAL``: System is in a non-normal flight mode. It can however still navigate.
        * ``EMERGENCY``: System is in a non-normal flight mode. It lost control over parts
          or over the whole airframe. It is in mayday and going down.
        * ``POWEROFF``: System just initialized its power-down sequence, will shut down now.

def system_status(self):
        """
        System status (:py:class:`SystemStatus`).

        The status has a ``state`` property with one of the following values:

        * ``UNINIT``: Uninitialized system, state is unknown.
        * ``BOOT``: System is booting up.
        * ``CALIBRATING``: System is calibrating and not flight-ready.
        * ``STANDBY``: System is grounded and on standby. It can be launched any time.
        * ``ACTIVE``: System is active and might be already airborne. Motors are engaged.
        * ``CRITICAL``: System is in a non-normal flight mode. It can however still navigate.
        * ``EMERGENCY``: System is in a non-normal flight mode. It lost control over parts
          or over the whole airframe. It is in mayday and going down.
        * ``POWEROFF``: System just initialized its power-down sequence, will shut down now.
        """
        return {
            0: SystemStatus('UNINIT'),
            1: SystemStatus('BOOT'),
            2: SystemStatus('CALIBRATING'),
            3: SystemStatus('STANDBY'),
            4: SystemStatus('ACTIVE'),
            5: SystemStatus('CRITICAL'),
            6: SystemStatus('EMERGENCY'),
            7: SystemStatus('POWEROFF'),
        }.get(self._system_status, None)