The CHIME Pathfinder is a new interferometric radio telescope that uses a hybrid FPGA/GPU FX correlator. The GPU-based X-engine of this correlator processes over 819 Gb/s of 4+4-bit complex astronomical data from N=256 inputs across a 400MHz radio band. A software framework is presented to manage this real-time data flow, which allows each of 16 processing servers to handle 51.2 Gb/s of astronomical data, plus 8 Gb/s of ancillary data. Each server receives data in the form of UDP packets from an FPGA F-engine over the eight 10 GbE links, combines data from these packets into large (32MB-256MB) buffered frames, and transfers them to multiple GPU co-processors for correlation. The results from the GPUs are combined and normalized, then transmitted to a collection server, where they are merged into a single file. Aggressive optimizations enable each server to handle this high rate of data; allowing the efficient correlation of 25MHz of radio bandwidth per server. The solution scales well to larger values of N by adding additional servers.
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