  As from the run 3 of CERN LHC scheduled in 2022, the upgraded ALICE
experiment will use a Common Readout Unit (CRU) at the heart of the data
acquisition system. The CRU, based on the PCIe40 hardware designed for LHCb, is
a common interface between 3 main sub-systems: the front-end, the computing
system, and the trigger and timing system. The 475 CRUs will interface 10
different sub-detectors and reduce the total data throughput from 3.5 TB/s to
635 GB/s. The ALICE common firmware framework supports data taking in
continuous and triggered mode and forwards clock, trigger and slow control to
the front-end electronics. In this paper, the architecture and the data-flow
performance are presented.
