Front End Crates

Signals from the detectors are processed by boards in VME, VXI, or CAMAC crates. These boards are then read out by a processor referred to as a "read out controller" (ROC). Generally, a single ROC handles only one crate of electronics (for performance reasons). The ROC serves 3 main functions: (1) read event data; (2) send event fragments to the event builder; and (3) perform setup and initialization functions on its crate of electronics at the request of the host computer. The ROC for FASTBUS is the FSCC (FASTBUS Smart Crate Controller), a Fermilab designed board manufactured by BiRa. It is a sequencer based single board design with an on-board 68020 and an ethernet interface. The VxWorks operating system has been ported to the FSCC at CEBAF, and it has passed performance tests. Established measurements confirm a 20Mbyte/sec handshaked data transfer rate and up to 40 Mbyte/sec read rate for high performance slaves implementing pipeline transfers. A slot addressing overhead of $\le$ 10 $\mu$sec under processor control has been measured with currently supported FB library routines (sequencer controlled AS/AK lock time has not been measured). In addition to the ethernet interface there is a sequencer controlled parallel output port capable of transferring data (10-20 meters) at 40Mbytes/sec into a VME based dual ported memory. For VME and VXI, single board computers running VxWorks (68K based) are required. These boards are available from a large number of manufacturers with VxWorks support. CEBAF is currently using Motorola's MVME167and MVME162 68040 boards. For a VME FDDI interface CEBAF has implemented the Rockwell CMC1150 series with a VxWorks Driver support package from Ross Microsystems. For users requiring CAMAC front end crates, the Kinetic Systems VME interface (model KS 2917) is supported (requires KS 3922 crate controller). Direct CAMAC readout through the CES VCC2117 Smart Crate Controller (with ethernet interface) is also supported. Since all CAMAC I/O is done through the CAMAC standard routines, any other interface for which these routines are available will also work (e.g. the CES branch highway interface).