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HK: Fachverband Physik der Hadronen und Kerne

HK 70: Instrumentierung XIV

HK 70.3: Vortrag

Freitag, 19. März 2010, 14:30–14:45, HG ÜR 6

Time synchronization and measurements of a hierarchical DAQ network — •Frank Lemke¹, Sebastian Manz², and Wenxue Gao¹ — ¹ZITI University of Heidelberg, Germany — ²KIP University of Heidelberg, Germany

The Data Acquisition (DAQ) system for the Compressed Baryonic Matter (CBM) experiment at the Facility for Antiproton and Ion Research (FAIR) in Darmstadt will introduce different challenges. Expected raw data rates of about 1 TB/s require online filtering and preprocessing. Detectors run in a self triggered time stamped mode depending on precise time distribution and synchronization. A readout chain has been developed, composed of a Read-Out-Controller (ROC) interfacing front-end electronics, a Data-Combiner-Board (DCB) combining data and an Active-Buffer-Board (ABB) buffering, reorganizing and transferring data via PCI express to the memory of a cluster computing node. The chain communicates via optical fibers at 2.5 Gbps. A compact control system is embedded in the ROC. A link protocol has been defined, involving three traffic classes, Data Transfer Messages, Detector Control Messages and Deterministic Latency Messages, which allow precise time distribution and synchronization within the DAQ system. The optical link is also used for clock distribution, the recovered link receive clock processed in a jitter cleaner PLL can be used as local system clock and as transmit clock. A DMA engine is implemented in the ABB to transfer data from the event buffer to the host node. Performance tests running Linux 2.6 in the end node delivered 224 MB/s bandwidth. Prototype systems are in a reliable status.