A high-throughput input interface for the CBM FLES

¹ Johann Wolfgang Goethe-Universität Frankfurt, Frankfurt am Main, Germany
² Frankfurt Institute for Advanced Studies, Frankfurt am Main, Germany
³ GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany

^* e-mail: hutter@compeng.uni-frankfurt.de

Published online: 7 October 2025

Abstract

The CBM First-level Event Selector (FLES) serves as the central data processing and event selection system for the upcoming CBM experiment at FAIR. Designed as a scalable high-performance computing cluster, it facilitates online analysis of unfiltered physics data at rates surpassing 1 TB/s.

As the input to the FLES, the CBM detector subsystems deliver free-streaming, self-triggered data to the common readout interface (CRI), which is a custom FPGA PCIe board installed in the FLES entry nodes. A subsystem-specific part of the FPGA design time-partitions the input streams into context-free packages. The FLES interface module (FLIM), a component of the FPGA design, acts as the interface between the subsystem-specific readout logic and the generic FLES data distribution. It transfers the packed detector data to the host’s memory using a low-latency, high-throughput PCIe DMA engine. This custom design enables a shared-memory-based, true zero-copy data flow.

A fully implemented FLIM for the CRI board is currently in use within CBM test setups and the FAIR Phase-0 experiment mCBM. We present an overview of the FLES input interface architecture and provide performance evaluations under synthetic as well as real-world conditions.