A microprocessor farm architecture for high speed data acquisition and analysis

The DO Level-2 data acquisition system has been previously described. This paper discusses the requirements and architecture of the system as well as its current status, and then considers its implementation using a new generation of hardware which is currently under development. The high interaction rates (--100 KHz) and data reduction requirements (250 Kbytes/event) associated with colliding beams experiments such as DO, necessitate the use of a hierarchial trigger design. The Level-O trigger uses scintillator arrays to provide an interaction time and rough position measurement. Using this information, as well as additional information received from fast detector outputs, the hardware based Level-1 trigger provides event selection in the 3.5 microsecond time between beam crossings. This primary filtering reduces the event rate to 200-400 events/second. The Level-2 data acquisition system uses a programmable software filter to further reduce this event rate to a reasonable recording rate of 1-2 Hz. Given the anticipated requirement of 100,000 instructions for filtering an event, the Level-2 system must be capable of 40 MIPs, as well as an I/O bandwidth in excess of 100 Mbytes/sec in order to empty the front end electronics without dead time. Since the individual events are totally uncorrelated, this is an ideal problem for parallel processing