Global data processing system with onboard CPU cards for the Belle II experiment

In the data acquisition (DAQ) system of the Belle II experiment, COmmon Pipeline Platforms for Electronics Readout (COPPER) boards developed at KEK are to be used for the unified interface with front-end detectors, except for an innermost pixel detector which needs a dedicated data reduction system. A COPPER board receives and processes the data from the front-end electronics via common optical links (Belle2-link) and send them to readout PCs. We developed DAQ software running on an onboard CPU card. The basic functions of this DAQ software is to read data from the hardware FIFO on a COPEPR board, check the data contents and send them to a downstream readout PC via Gigabit Ethernet. After tuning the DAQ software, the CPU usage is now less than 60% to handle 1kB/event size data with a constant 28.7 kHz even rate, which is acceptable for the operation with full luminosity in the Belle II experiment. In this report, we present the DAQ software system on a COPPER board and its performance in processing data.