Commissioning and performance of the Preshower off-detector readout electronics in the CMS experiment

The CMS Preshower is a fine grain detector that comprises 4288 silicon sensors, each containing 32 strips. The raw data are transferred from the detector to the counting room via 1208 optical fibres producing a total data flow of ~72GB/s. For their readout, 40 multi-FPGA 9U VME readout boards are used. This article is focused on the testing & commissioning of the VME readout system using two tools: a custom connectivity test system based on FPGA embedded logic analyzers read out through JTAG; an FPGA-based system that emulates the data-traffic from the detector. Additionally, the performance of the VME readout system in the CMS experiment, including the 2009 CRAFT run (Cosmic ray at Four Tesla), is discussed.