Deterministic and flexible communication for real-time embedded systems

The research work conducted during the PhD program was focused on real-time embedded systems communication, in particular, for what concerns the determinism and flexibility perspectives. To this aim, research activities were carried out based on a widespread real-time communication protocol, namely, the Controller Area Network (CAN). Indeed, CAN is the de facto standard in automotive and more recently, it also gained popularity in industrial automation and various kinds of networked embedded systems. Determinism is of paramount importance in communication, since it directly affects timing accuracy. However, deterministic communication cannot be achieved without a comprehensive understanding of possible sources of delay and jitter in a CAN-based distributed system, and more importantly, their countermeasures. Even if all the other sources of jitter are removed or mitigated, the bit stuffing (BS) mechanism the CAN physical layer relies on still introduces a non-negligible amount of variability into the frame transmission time. To solve this problem, first of all, two novel encoding schemes, namely 8B9B and VHCC, were designed and implemented to prevent bit stuffing in the CAN payload. More specifically, VHCC enhanced the fixed length 8B9B payload encoding in terms of encoding efficiency by means of packing sub-byte information. After that, a Zero Stuff-bits CRC (ZSC) mechanism was invented to tackle remaining bit stuffing jitter in the Cyclic Redundancy Check (CRC) of a CAN frame. In this way, it is possible to eliminate bit stuffing jitter completely from all over the frame and achieve jitterless CAN communication. Concerning this activity, an Italian patent application has been submitted and a European extension is under preparation. For what concerns flexible communication, we extended CAN in both the real-time and non real-time domains. On the one hand, the application scenarios of CAN were largely broadened by making it support the most widely used general-purpose communication protocol, namely the Internet Protocol (IP). On the other hand, in the real-time domain, a transport protocol was designed and implemented to support Modbus on CAN. Modbus is an application layer real-time communication protocol widespread in industrial and building automation. This work was adopted by industry for local subsystem communication. And more importantly, it paves the way for CAN in building automation. Knowledge and experience gained in embedded system design and development are readily applied to further research and transferred into technology suitable for real-world applications.