FELIX: first operational experience with the new ATLAS readout system and perspectives for HL-LHC

Over the next decade, the ATLAS detector will be required to operate in an increasingly harsh collision environment, with ten times more trigger rate. To maintain physics performance, the detector will undergo a series of upgrades. In particular, it will improve the capacity and flexibility of the detector readout system. To this end, the Front-End Link eXchange (FELIX) system was developed as the new interface between the data acquisition; detector control and TTC (Timing, Trigger and Control) systems; and new or updated trigger and detector front-end electronics. FELIX functions as a router between custom serial links from front end ASICs and FPGAs to data collection and processing components via a commodity switched network. The serial links may aggregate many slower links or be a single high bandwidth link. FELIX also forwards the LHC bunch-crossing clock, fixed latency trigger accepts and resets received from the TTC system to front-end electronics. FELIX uses commodity server technology in combination with FPGA-based PCIe I/O cards. FELIX servers run a software routing platform serving data to network clients performing a number of data preparation, monitoring and control functions. This paper covers the design of FELIX as well as the first operational experience gained during the Run 3 starting, including the challenges faced commissioning the system for each ATLAS sub-detector. Finally, the planned evolution of FELIX for High-Luminosity LHC will be described, including architectural changes and status of early integration with detector development projects.