Münster 2011 – wissenschaftliches Programm

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HK: Fachverband Physik der Hadronen und Kerne

HK 20: Instrumentierung IV

HK 20.7: Vortrag

Dienstag, 22. März 2011, 15:45–16:00, HS1

Experiences and results using the CBMnet protocol including precise time synchronization and clock distribution — •Frank Lemke, Sven Schenk, and Ulrich Bruening — ZITI University of Heidelberg, Mannheim, Germany

Within the context of the Compressed Baryonic Matter (CBM) experiment at the Facility for Antiproton and Ion Research in Darmstadt a Data Acquisition (DAQ) system has been built using the CBMnet protocol on unified optical connections. For beam time tests in 12/2010 a hierarchical DAQ was built that consisted of 8 Read-Out Controllers (ROC) collecting data from different detectors, attached in groups of 4 to 2 Data Combiner Boards (DCB). Each DCB used an Active Buffer Board (ABB) as data sink and for both another ABB serves as clock distribution and synchronization source. In order to use Deterministic Latency Messages (DLM) for synchronizing the network path to the detectors all clocks within the network had to be derived from one base clock. The arrival of a DLM in a ROC triggers a reset of epoch counters required by the compute nodes to combine collected data of different ROCs. Clock distribution worked reliably and by reducing the jitter of some recovered clocks to less than 10ps RMS, the goal of deterministic timing and synchronization over optical links has been achieved. The CBMnet protocol, that merges synchronization and clock distribution as well as control messages and detector data into virtual channels on the unified optical link, worked well. The experiences gained and also some new detector requirements lead to new ideas for further refinements such as unbalanced lane handling and long message support.