The main objective of the CMS Electronique project is the development of an electronic device called the selective read-out processor for the electromagnetic calorimeter (SRP for Selective Read-out Processor) of the CMS experiment. The SRP is part of the read-out electronics of the "Off-Detector" calorimeter due to its location in the underground service cavern outside the experimental cavern. For each event accepted by the first level of the trigger system of the experiment, the SRP must allow to decrease in real time the quantity of calorimeter raw data before being sent to the acquisition system. In spite of a considerable reduction factor (from 15 to 20) to be obtained, the physical performance of the calorimeter must not be compromised.

Themes and programs

Innovation for detection systems / Signal processing and real-time systems


The design and realization of the off-detector electronics are shared between the following laboratories:

  • Cern: configuration boards for front-end electronics and clock distribution and various control signals;
  • Irfu: Selective Read-out Processor boards SRP
  • LLR Palaiseau: maps of trigger primitive generation
  • LIP Lisbon: memory buffer boards




Means of investigation


  • Study of parallel optical technologies and very high speed serial links of FPGA electronic components. These technologies are proposed for communication links of the SRP with other subsystems of the off-detector read-out electronics
  • Study of the use of embedded processors in the new generation FPGAs
  • Study of selective read-out algorithms and their performance



Industrial development kits and associated software for the parallel optical components and new generation FPGAs. Very high performance serial link analyzer.



  • great number of PRS input / output links - about 200;
  • High bandwidth - 1.6 Gbit / s (see 2.5 Gbit / s) per link;
  • Asynchronous operation at level 1 trigger frequency - up to 100 kHz;
  • Limited time budget - 5 -Fìs;-A
  • Flexibility in selecting selection algorithms using FPGA type programmable wired logic.

The SRP consists of 12 identical boards complying with the VME64x standard. Each board can be used for the barrel and endcap regions of the electromagnetic calorimeter. It can also serve as the test instrument for other SRP boards.




Contribution from Irfu


Scientific and technical responsibilities

  • Coordination of the collaboration "Off - Detector Electronic" at Cern;

  • Definition of selective read-out algorithms;

  • Definition of the global architecture of the selective read-out device;

  • Definition of the communication links of the SRP with other subsystem of the Off-detector read-out electronics;

  • Design and implementation of the SRP.

  Study of selective read-out algorithms
  Design and implementation of the selective read-out device




Status and perspectives

Important Dates

  • April 2002: Association of Irfu (at the time DAPNIA) with the "Off-detector Electronics" collaboration
  • June 2003: Launch of the CMS Electronics project at Irfu
  • September 2003: Participation in the "Addendum to CMS ECAL Technical Design Report"
  • December 2003: Validation of parallel optical technology for SRP communications links
  • May 2004: Review by the CMS collaboration of Electronics System Review: approval of the architecture of the SRP
  • June 2004: Demonstration of the operation of the SRP under the temporal constraint of 5-Fìs-A
  • November 2006: "SRP Electronics system review" at CERN: demonstration to the evaluation committee of the operation of the SRP on two prototype boards; Agreement for mass production of final boards
  • January 2007: Launch of series production
  • March 2007: Tests at CERN in a subset of the non-detector electronics
  • June 2007: End of production of SRP final boards
  • August 2007: End of serial production of SRP boards
  • September 2007: Installation of SRP "Barrel" boards at Cern
  • February 2008: Installation of SRP "Endcap" boards at Cern
  • June 2008: Integration of the "Barrel" SRP boards into the ECAL read-out system


  • June 2004: Validation of the parallel optical technology for the communication links of the SRP and validation of the operation of the SRP under the temporal constraint of 5-Fìs-A
  • December 2006: End of the prototyping phase
  • June 2007: End of production of SRP final boards



#3881 - Last update : 02/08 2017


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