Time-based Distributed Scheduling under Linux

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Dr. Kovácsházy Tamás
Department of Measurement and Information Systems

Nowadays the general purpose Ethernet-based communication solutions are more and more widespread, think for example to the TCP/IP protocol suite which creates the basis of the Internet or those Ethernet-based technologies of which popularity is growing in various industries. However due to the operation of traditional TCP/IP communication it is not suitable for real-time tasks that are often emerge in industrial applications. The demand for standard solutions had quickly come up which can be used with the general purpose communication infrastructure to enable real-time Audio/Video transmission or the implementation of a real-time distributed control system. The Time-Sensitive Networking (TSN) will provide a solution to these demands, but it is still under standardization. One of the key components of TSN is that the elements of the network are synchronized in time with great precision and the scheduling of the system's activities and the shaping of communication traffic are based on this common time scale, in compliance with the prescribed rules.

In my thesis I'm looking for solutions to the following problem. If we have a network of embedded devices in which each node runs an embedded Linux operating system, how could we connect the PTP clock synchronization protocol which is defined in the IEEE 1588 standard, that provides sub-microsecond accuracy with the scheduling of real-time local activities running on Linux. My thesis first introduces the PTP based precise clock synchronization and the usage of it's linuxptp implementation. I've implemented the clock synchronization on two different SoC (System on a Chip) platforms, both provides hardware timestamping for the proper use of PTP. The method of evaluating the results of the clock synchronization with sub-microsecond accuracy is also unclear, to solve this we can use for example accurate PPS (Pulse Per Second) signals. I also provide solutions to produce a sufficiently accurate PPS signal on both platforms I have used, even if the processor did not support the generation of a PPS signal directly. Finally, I will examine the capabilities of the embedded Linux nodes of the network to schedule tasks based on the synchronized local clocks. The solutions I will raise in my thesis will also be demonstrated in sample applications as well as their performance and constraints will be evaluated on the basis of several measurement results.


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