Event Builder

The event builder constructs a complete event data from detector signals. Data are sent from seven VME crates of the FASTBUS TDC readout systems and four SVD VME crates. The output of the event builder is connected to six VME crates of the online computer farm. We use 1.2 Gbps ECL-level line, G-Link, for the data transfer layer [88] . The event builder is a barrel shifter consisting of 12 transmitters, 6 receivers and a set of and barrel shifter switches. The data path and the control path are shown in Fig. . The barrel shifting sequence is controlled by an external controller through a 50 Mbps serial line, TAXI. The barrel shifter switches the configuration event-by-event according to the configuration given by the external controller to form an event. The readout VME crates are located in the electronics hut near the detector, while the farm crates are in the control room. Thus a long connection of about 100 m is required. G-Link signals are transferred via optical fibers, and TAXI signals are transferred by unshielded twisted pair cables. The transmitter and receiver modules are built as S-Bus adaptor cards, so that the VME SPARC CPU, FORCE CPU-7V, can be used as the controller. We are using Solaris OS for the control software.

Figure: The data flow and the control flow of the event builder.