Data acquisition

The data acquisition (DAQ) system was designed to work within the limiting features of the front-end electronics such that it introduces no additional dead-time. The analog-to-digital conversion time of the S/H's and the restriction that data transmission cannot occur while the front-end electronics are active determines the dead-time. This has led to a scheme where the data conversion occurs rapidly (1 s) and the datum from each conversion is sent immediately to a remote buffer. Each front-end crate has a 16-bit wide, 12 MByte/s point-to-point link to a dedicated VSB dual-port memory. A typical crate has 2000 front-end channels and the total conversion and transfer time is 2 ms. This contributes 0.2%dead-time per Hz of level 2 trigger rate. The dual-port memories are serviced by a number of VME processors that do sparsification and event fragment assembly in a distributed fashion. The finished events are transferred via Ethernet to a workstation running the level 3 trigger code. The average CLEO hadronic event is presently about 8 kByte and the average readout event is 5 kByte.