1. Faculty of Sciences, Scuola Normale Superiore, Pisa, Italy
2. Real-Time Systems Laboratory (RETIS), TECIP Institute, Scuola Superiore Sant’Anna, Pisa, Italy
3. Department of Computer Science, University of Pisa, Pisa, Italy
4. Institute of Informatics and Telematics, National Research Council of Italy, Pisa, Italy