Bonn 2010 – wissenschaftliches Programm
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.