## 6 Conclusions and Future Work  
Cyber-physical systems require a tight combination of and coordination between computational and physical processes. These systems resulted in the recent years from the confluence of technologies in embedded systems, distributed systems, dependable systems and often real-time systems with advances in networking, microcontrollers, sensors, actuators and even artificial intelligence. Time- and safety-critical CPSs must operate safely, securely, efficiently and in real-time, and therefore predictability with regards to timing and security requirements is critical for their development. To identify the key issues involved in the development of these systems, in this position paper, we first draw a parallel between embedded systems and CPSs. We then explore the research and look into a number of existing frameworks and techniques devoted to developing timing predictable and secure safety-critical embedded systems. We conclude that the state of the art in the embedded systems domain is inadequate for the more complex and open industrial CPSs, as the boundaries of the CPS extend beyond the system's network interfaces. Furthermore, the existing techniques and frameworks for the verification of timing predictability in embedded systems are based on the assumptions about the system and its environment. Shifting from embedded systems to CPSs, these assumptions do not hold anymore, as even if a time-critical CPS is proven to be timing predictable at the design time, the predictability of the system can be jeopardized when the system is executed at the run-time due to security threats on the data entering the system via its sensors, networks, other CPSs or even the cloud. We make a strong case to advocate that timing predictability should be considered a prerequisite for functional safety, while security should be considered a prerequisite for both timing predictability and functional safety. We also conclude that the existing techniques and frameworks for building timing predictable CPSs hold only if the data integrity, authentication and authorization are supported. Therefore, we argue that there is a gap and future work should be devoted to developing frameworks that render security as a prerequisite for time- and safety-critical CPSs. In addition to all the above, we highlight that CPSs can leverage formal verification to guarantee safe system operation at design time, as well as use artificial intelligence to act well in open environments. We illustrate our ideas and position on one such system, namely the autonomous quarry.  
Conceptualization, S.M., E.L. and A.V.F.; methodology, S.M.; investigation, S.M., E.L. and A.V.F.; writing--original draft preparation, S.M., E.L. and A.V.F.; writing--review and editing, S.M. and E.L. All authors have read and agreed to the published version of the manuscript.  
The work in this paper was supported by the Swedish Governmental Agency for Innovation Systems (VINNOVA) through the project DESTINE, the Swedish Foundation for Strategic Research (SSF) through the project Serendipity, and the Swedish Knowledge Foundation (KKS) through the projects HERO and DPAC.  
**Acknowledgments:** The authors would like to thank the industrial partners Volvo CE, Ericsson, and Arcticus Systems, among others. Finally, thanks to the anonymous reviewers for their valuable input.  
**Conflicts of Interest:** The authors declare no conflict of interest.