The charged trigger system of NA48 at CERN

The NA48 charged trigger is a mixed hardware and software real-time process ing system intended to detect the interesting configurations of K-o charged decays. It achieves real-time event building, track reconstruction and kin ematics computation on drift chamber data at an event rate of 100 kHz and w ithin a maximum decision latency of 100 mu s. The system uses data driven, FPGA-based coordinate builders, a hardware event builder based on a crossba r switch, and a farm of up to 16 event processors for its software part. It has been installed and operated at CERN since 1995. After a description of the constraints and architecture of the various subsystems, the paper give s an account of the results and performance of the system based on the 1996 /1997 runs. More specifically, the replacement of the present DSP-based imp lementation of the processing farm by RISC processors will be discussed. (C ) 1998 Elsevier Science B.V. All rights reserved.