Mixed-criticality cyber physical system provides great advantages in terms of cost, dependability, scalability and competitiveness. However, especially due to shared resources, the certification of these kind of systems is still challenging. Furthermore if the power management is integrated in the system, compliance with safety and security is even more complex. This paper presents the safety concept of a railway signalling use–case, considering a mixed-criticality object controller which includes a power management approach. The paper presents a proposal of using degraded modes and a safety/security analysis of low power techniques. The concept has been positively assessed by an independent certification body.