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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def swo_start(self, swo_speed=9600):
 """Starts collecting SWO data. Note: If SWO is already enabled, it will first stop SWO before enabling it again. Args: self (JLink):
 the ``JLink`` instance swo_speed (int):
 the frequency in Hz used by the target to communicate Returns: ``None`` Raises: JLinkException: on error """

        if self.swo_enabled():
            self.swo_stop()

        info = structs.JLinkSWOStartInfo()
        info.Speed = swo_speed
        res = self._dll.JLINKARM_SWO_Control(enums.JLinkSWOCommands.START,
                                             ctypes.byref(info))
        if res < 0:
            raise errors.JLinkException(res)

        self._swo_enabled = True

        return None