Time-Predictable Communication on a Time-Division Multiplexing Network-on-Chip Multicore

This thesis presents time-predictable inter-core communication on a multicore platform with a time-division multiplexing (TDM) network-on-chip (NoC) for hard real-time systems. The thesis is structured as a collection of papers that contribute within the areas of: reconfigurable TDM NoCs, static TDM scheduling, and time-predictable inter-core communication.

More specifically, the work presented in this thesis investigates the interaction between hardware and software involved in time-predictable inter-core communication on the multicore platform. The thesis presents: a new generation of the Argo NoC network interface (NI) that supports instantaneous reconfiguration, a TDM traffic scheduler that generates virtual circuit (VC) configurations for the Argo NoC, and software functions for two types of intercore communication.

The new generation of the Argo NoC adds the capability of instantaneously reconfiguring VCs and it addresses the identified shortcomings of the previous generation. The VCs provide the guaranteed bandwidth and latency required to implement time-predictable inter-core communication on top of the Argo NoC. This new Argo generation is, in terms of hardware, less than half the size of NoCs that provide similar functionalities and it offers a higher degree of flexibility to the application programmer.

The developed TDM scheduler supports a generic TDM NoC and custom parameterizable communication patterns. These communication patterns allow the application programmer to generate schedules that provide a set of VCs that efficiently uses the hardware resources. The TDM scheduler also shows better results, in terms of TDM period, compared to previous state-of-the-art TDM schedulers. Furthermore, we provide a description of how a communication pattern can be optimized in terms of shortening the TDM period.

The thesis identifies two types of inter-core communication that are commonly used in real-time systems: message passing and state-based communication. We implement message passing as a circular buffer with the data transfer through the NoC. The worst-case execution time (WCET) of the send and receive functions of our implementation is not dependent on the message size. We also implement five algorithms for state-based communication and analyze them in terms of the WCET and worst-case communication delay. The five algorithms each have scenarios where they are better than the others.

This thesis shows in detail how time-predictable inter-core communication can be implemented in an efficient way, from the low-level hardware to the high-level software functions.