Swallow: Building an energy-transparent many-core embedded real-time system

Swallow is a many-core platform of interconnected embedded real time processors with time-deterministic execution and a cache-less memory subsystem. Its largest current configuration is 480 × 32-bit processors. It is open-source, designed from the ground up to allow the exploration of flexibility, scalability and energy efficiency in large systems of embedded processors. Further, it enables the behavior of various structures of parallel programs to be explored. It is a proof of concept and design example for other potential systems of this kind. We present the energy transparency features and proportional energy scaling of the system that allows it to be expanded beyond hundreds of cores. We discuss the design choices, construction and novel network implementation of Swallow. Currently, the system provides up to 240 GIPS, with each core consuming 71-193mW, dependent on workload. Its power per instruction is lower than almost all systems of comparable scale. We discuss the challenges associated with efficiently utilizing this system, particularly communication/computation ratios, and give recommendations for future systems and their software.