If its urgent to travel from Chennai to Bangalore and dont have direct train at the time ....take any train towards Jolarpettai and get down at VANIYAMBADI or AMBUR (Kovai Exp has no stop at Vaniyambadi).......Many buses plying on Asian Highway 45 (AH45) will take you to Bangalore via Krishnagiri, Hosur in 2h 30min to 3hr.