THE COMPASS RICH-1 READ-OUT SYSTEM

to be announced

INFN, Sezione di Trieste and ICTP, Trieste, Italy
on behalf of the COMPASS RICH group

   COMPASS RICH-1 is a gas radiator RICH employing MWPCs with CsI photo cathodes as photon detectors; the total active area is about 5.5 m2. The electronics takes the analog signals coming from the ~83 thousand channels.
   The read-out system is mainly performed by 192 BORA boards. The BORA is a large front-end board (432 channels) with local intelligence based on a tightly interacting DSP-FPGA couple. The 192 front-end boards are controlled via a dedicated PC resident board: DOLINA, equipped with 8 DSPs. Eight parallel DSP nets consisting of 25 DSPs each (one in DOLINA and the others in 24 BORA boards) allow data transfer from / to the PC.
   All BORAs are optoisolated from the DOLINA board, and each BORA has two optical fibres to communicate with the DAQ electronics, avoiding this way grounding interference. One optical fibre is used to receive the trigger and the other is used to send data.
   The BORA front-end electronics starts with 27 16-channel COMPASS-Gassiplex chips which take the 432 signals coming from the photon detectors. The analog output of these chips are digitised in 10bits at 40 MSamples/sec and these digital values are written into FIFO memories which can store up to 100 events. The content of these FIFOs is read and processed by the FPGA. The FPGA stores absolute thresholds of all channels and subtract them from the digitised signals. Only values above thresholds are framed and sent through the optical fibre to the global DAQ. The FPGA works in different modes (calibration, acquisition, etc.) according to what is requested by the DSP. The DSP calculates pedestal and noise of all channels if it is required.
   The board has built in self-test facilities, and provides engineering frames containing hoard temperatures and voltages for monitoring purposes. The read-out system can steadily work up to an event rate of 75 kHz with occupancies up to 20%, reaching an effective transmission data rate of 8.64 Gbytes/sec.
The system is described in details and its performances during the first year of COMPASS experiment operation are given.