Method of functionality testing for a ring oscillator

A method and apparatus is provided for testing the logic functionality and electrical continuity of a ring oscillator comprising an odd number of inverters connected to form a closed loop. In the method and apparatus, a known value is forced through the ring oscillator, to test the complete circuit path thereof. Thus, a low overhead deterministic test of the functionality of the ring oscillator is provided. In a useful embodiment of the invention, a method is provided for testing functionality and electrical continuity in a ring oscillator, wherein a first test device is inserted between the input of a first inverter and the output of an adjacent second inverter. The first test device is then operated to apply first and second test bits as input test signals to the first inverter input. The embodiment further comprises detecting the response to the applied first and second test bit signals at the output of the second inverter, and using the detected responses in providing an evaluation of functionality of the ring oscillator.