A mechanism is provided for minimizing power consumption for operation of a fixed-frequency processing unit. The packet presents at least two main faces of which a first face appears flat and a second face is composed of a substantially central flat portion and two curved portions by which the flat portion is connected to the longitudinal edges of the flat first face, so that when viewed in cross section the packet presents a substantially semicircular shape, or that of a rounded isosceles trapezoid. A microprocessor outputs a plurality of test signals responsive to the test requests.