Building a reliable, scalable and affordable RTC for AO instruments on ELTs

Addressing the unprecedented amount of computing power nee ded by the ELTs AO instruments real-time controllers (RTC) is one of the key technolo gical developments required for the design of the next generation AO systems. Throughput oriented arch itectures such as GPUs, providing orders of magnitude greater computational performance than high-en d CPUs, have recently appeared as attractive and economically viable candidates since the fast emergenc e of devices capable of general purpose computing. However, using for real-time applications a I /0 device which cannot be scheduled nor controlled internally by the operating system but is sent commands thro ugh a closed source driver comes with a number of challenges. Building on the experience of almost real-time end-to-end simulations using GPUs, and relying on the development of the COMPASS platform , a unified and optimized framework for AO simulations and real-time control, our team has engag ed into the development of a scalable, heterogeneous GPU-based prototype for an AO RTC. In this paper, we eview the main challenges arising when utilizing GPUs in real-time systems for AO and rank them in terms of impact significance and available solutions. We present our strategy, to mitigate t hese issues including the general architecture of our prototype, the real-time core and additional dedicated components for data acquisition and distribution. Finally, we discuss the expected performance in terms of latency and jitter on the basis of realistic benchmarks and focusing on the dimensioning of the MICADO AO module RTC.