COMPASS Spill Buffer
(Technische Universität München)


COMPASS uses S-LINK in the DAQ system. To make use of the spill cycle of the SPS (2.4 sec beam every 14.4 sec until 2001, then 5.1 sec every 16.8 sec) to reduce the effective data rate, COMPASS is designing a Read-Out Motherboard having a buffer of up to 512 Megabytes that can receive all data from one spill before reading it out much slower over a PMC or PCI bus. This way one PC can handle several Read-out Motherboards.

A PCI card is being built that has the RAM memory and the PCI interface integrated. The design is basically an S-LINK FIFO connected to the S-LINK to PCI interface that has been in production since 1997. The S-LINK Link Destination Card can be plugged on top of this card. The two boards together will take up only one PCI slot, just like the S-LINK to PCI interface.

By January 1999, 10 to 15 prototype cards were needed, while in the end of 1999 another 22 cards were built. By the end of the year 2000 in total 64 cards are needed.

In 2001 a new card based on Xilinx Virtex with SDRAM memory was developed. The Xilinx BGA chip incorporates the S-Link logic, FIFOs, SDRAM control logic and the interface to the AMCC PCI chip.

Schematics of COMPASS spill buffer
Schematics of the COMPASS spill buffer card


14 May 1997 the S-LINK to PCI design files were given to Igor Konorov
26 November 1997 the PCB of the designed interface is received
26 January 1998 all components expected in by beginning of February
2 April 1998 programmed two sets of PALs at CERN. Tested mechanics. All OK. One board is being assembled, while a second board will follow soon
25 August 1998 board tested with SLIDAS and very simple software, it worked well without any problems. 
April 1999 The prototype is integrated in an existing testbeam at X5 to read silicon microstrip detectors. 3 cards are read in one PC.
September 1999 The debugged protoype is combined with the CATCH board to form the skeleton of the COMPASS readout system. Triggering is provided by the trigger control system TCS.
2000 COMPASS has a technical run with 10% of the equipment on the floor. The radout is done with 30 64 MB spillbuffers.
2001 A new version of the board with SDRAM and Xilinx was designed in spring. During the commisioning run a mixed system with old 64 MB cards and new 512 MB SDRAM cards was used, in total 53 spillbuffers. Adapted to bandwidth needs FSC S-Links, Single and Double ODIN S-Links are used.
2002 During the first physics run of COMPASS only SDRAM cards are used, in total 62 spillbuffers. New interrupt driven readout software was written giving a speed increase of about 2.5 times.



Documentation on the software is currently in preparation. As base a modified version of the driver for the AMCC 5933 by A. Cisternino is used. The main extension consists in implementing multiple instances of the device driver to use several identical boards in one computer. This version exists for Linux up to version 2.0, 2.2 and 2.4.

Test software is provided for Linux 2.2 and Linux 2.4 on a very preliminary basis.

A new interrupt controlled driver as used in COMPASS is provided along with test software and a plugin for the ALICE data acquistion software DATE. This driver is exclusively available for Linux 2.4.

The newest driver V4 also includes a slow backwards link via the S-link user return lines.

NEW Latest update Dec. 2008: The current version v5 for kernels 2.6 is recommended now. It is used since 2008. You need to apply the bigphysarea patch to the kernel.

No warranty is given that this software is useful or bug free. It is provided as is without documenation and support. It may also contain strong implications from an implementation particular to COMPASS and may not suit general cases of systems using S-Link. See the license terms concerning the use of this software as well as the driver software. For details on using the AMCC 5933 see the manual from AMCC




CERN - High Speed Interconnect - S-LINK
Lars Schmitt - 25 February 2003