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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_set_emu_buffer_size(self, buf_size):
 """Sets the size of the buffer used by the J-Link to collect SWO data. Args: self (JLink):
 the ``JLink`` instance buf_size (int):
 the new size of the emulator buffer Returns: ``None`` Raises: JLinkException: on error """

        buf = ctypes.c_uint32(buf_size)
        res = self._dll.JLINKARM_SWO_Control(enums.JLinkSWOCommands.SET_BUFFERSIZE_EMU,
                                             ctypes.byref(buf))
        if res < 0:
            raise errors.JLinkException(res)

        return None