<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def driver_name(self):
 """ Returns the name of the driver that provides this tacho motor device. """

        (self._driver_name, value) = self.get_cached_attr_string(self._driver_name, 'driver_name')
        return value