FPGA based event building and data acqiusition system for the COMPASS experiment

The purely software based old data acquisition system of the COMPASS experiment at CERN is replaced by the new hybrid FPGA-software system. The two level FPGA subsystem takes over the data handling role. The hardware is built in a compact AMC form factor using a Xilinx Virtex-6 VLX130T FPGA as a data processor. The data handling includes a 15:1 data link multiplexing and complete event building in firmware. All high speed links of the system are commutated by the 144×144 channels cross point switch which is used to provide dynamic load balancing. The designed throughput of the system is 1.6 GB/s while the maximum estimated data rate of the experiment is 1.5 GB/s for the 50 kHz trigger rate. The system makes use of the accelerator spill structure for optimizing the load on the read-out PCs. The distributed software runs on a server farm and integrates control and configuration functionality. The software closely monitors data flow for consistency on all stages of the event building process to perform load balancing and error recovery. The prototype of the system was successfully tested during the commissioning of the experiment and the full system will be used in the physics run 2015.