Progress in design and testing of the DAQ and data-flow control for the Phase-2 upgrade of the CMS experiment

The CMS detector will undergo a major upgrade for the Phase-2 of theLHC program the High-Luminosity LHC. The upgraded CMS detector willbe read out at an unprecedented data rate exceeding50 Tb/s, with a Level-1 trigger selecting eventsat a rate of 750 kHz, and an average event size reaching8.5 MB. The Phase-2 CMS back-end electronics will bebased on the ATCA standard, with node boards receiving the detectordata from the front-ends via custom, radiation-tolerant, opticallinks.The CMS Phase-2 data acquisition (DAQ) design tightens the integrationbetween trigger control and data flow, extending the synchronousregime of the DAQ system. At the core of the design is the DAQ andTiming Hub, a custom ATCA hub card forming the bridge between thedifferent, detector-specific, control and readout electronics and thecommon timing, trigger, and control systems.The overall synchronisation and data flow of the experiment is handledby the Trigger and Timing Control and Distribution System (TCDS). Forincreased flexibility during commissioning and calibration runs, thePhase-2 architecture breaks with the traditional distribution tree, infavour of a configurable network connecting multiple independentcontrol units to all off-detector endpoints.This paper describes the overall Phase-2 TCDS architecture, andbriefly compares it to previous CMS implementations. It then discussesthe design and prototyping experience of the DTH, and concludes withthe convergence of this prototyping process into the (pre)productionphase, starting in early 2023.