RICH 2014 Testbeam DAQ

Summary and Quick Start Guide

The front-end data are acquired by the DBs (digital boards) that are connected to the ECs (elementary cells). The DBs capture events in response to external triggers (pulser or beam), format the data into MEPs (multi-event packets) and transmit the MEPs to the DAQ PC using Gbit Ethernet. Configuration of the DAQ and the front end electronics is via the same Gbit Ethernet links. The DAQ PC is located in the beam area.

Control of the acquisition is done using Java GUIs. The JRichEcConfigurator GUI manages sets of elementary cell configuration parameters. The JRichEcControl GUI takes care of run control functions. These GUIs have superseded the ones used in the beam tests. The main difference is that the management of the EC configuration parameters and the run control functions have been separated. The GUIs are described in more detail in their respective topics. A helper program (feb-proxy, that is started automatically by the GUI) forwards configuration packets to the DBs over the network and receives the data packets from the front-end. The packets are decoded by feb-proxy and the data saved in MDF format, one file per DB.

To start the DAQ, first log on to the DAQ account on the DAQ PC. This is usually done using ssh -Y from a PC in the control room. Type the command start_daqgui at the prompt to start the GUI. Changes to the settings are saved by the GUI and the last saved settings are restored when the GUI is started. A second GUI is used to control and monitor the trigger sources. To start it, use the start_trigger command then click on the Connect button.

To start a run, first choose the desired trigger source from the trigger GUI (usually Pulser or Beam) then click Start on the DAQ panel to start acquiring data and Stop when you have finished. Data are saved to disk only if the Recording box is checked. The Save preferences box should also be checked to ensure that the settings are saved at the start of each run. The run number is incremented automatically when starting a new run but can also be manually set (set it to one less than the number you want for the next run).

The Trigger Logic and GUI

The trigger logic is implemented in an FPGA on a Nexys3 module and is controlled by a Java GUI. The trigger logic board receives an external beam trigger signal which is conditioned and fanned out to the DBs. The board can also generate pulser triggers that are fanned out in the same way. The logic also receives a gate signal from each connected DB indicating that it is ready to accept a trigger. Triggers are only sent when the gate signals of all connected DBs are asserted. The DBs may deassert the gate signal to prevent buffer overflow at high trigger rate. The gate signals are also used to disable triggers when a run is not in progress under control of the DAQ GUI.

The trigger outputs and gate inputs use LVDS differential signalling. The external trigger input is 50Ohm terminated LVTTL. One of the trigger outputs is sent to the beam telescope trigger input via an LVDS to LVCMOS translator.

The trigger GUI displays a number of counters:

Radio buttons allow to select between three trigger sources (Pulser, Beam or FEB) or None. Buttons are provide to reset the counters and to log the current values of the counters in the elog.

The logic board performs some conditioning of the external input by enforcing a minimum time between triggers of about 400ns.

-- StephenWotton - 13 Oct 2014