A voltage scalable device is known to be interesting for energy saving. It enables to reduce the general speed of the device and, therefore, its consumption. We already proposed a fast predictive control strategy to deal with this power-performance tradeoff in an electronic device supplied by two voltage levels and a continuously varying frequency. In this paper, the approach is extended to a fully discrete scheme with M possible voltage levels and N frequency levels. The proposed approach clearly gives an important reduction of the energy consumption with a very low control computational cost. Moreover, the control strategy is highly robust to tackle variability since it is not based on any parameters of the system.