The DAQPATH readout system of the Serenity boards for the CMS Phase-II Upgrade

The Serenity boards are ATCA custom boards used in the readout of the Phase-II CMS detector. Each board can handle up to 144 optical serial links (up to 25Gb/s each) and supports up to two high-performance FPGAs. In several applications the Serenity board is required to aggregate raw events (FE data) from the detector at every L1 accept and route this event fragment to the central DAQ system. The architecture and behavior of the DAQPATH firmware that collects and merges FE data and manages their transmission to the DAQ system over 25Gb/s output optical links are here described.