The data collection modules and ATM-based event builder for the PHENIX experiment at RHIC

The PHENIX experiment at RHIC will study 200 GeV/nucleon Au+Au collisions as well as pp and pA collisions at higher energies. In order to study hard processes or high-mass vector mesons, which have small cross sections, PHENIX emphasizes measuring charged hadrons, leptons, and photons at a high rate in a limited aperture. At design RHIC luminosity, the minimum-bias interaction rate will be approximately 1000 Hz with an average zero-suppressed event size of 200 kB. We will discuss two major parts of the PHENIX online system: the Data Collection Modules (DCM) and the Event Builder (EvB). The DCMs use a combination of FPGAs and DSPs to perform online pedestal subtraction, zero-suppression, and data formatting. They have been fully constructed and tested and are able to deliver data at a maximum rate of 160 MB/s. The Event Builder consists of commercially-available PCs and a 10 Gb/s ATM switch. The software for it has been developed using Windows NT, Winsock2 and Visual C++, allowing a fully object-oriented design. Currently, we are running topologies up to 4/spl times/3 which can deliver data at /spl sim/10MB/sec/node and performance is improving steadily.