Sep 25 – 29, 2006
Valencia, Spain
Europe/Zurich timezone

A Read-out Driver for Silicon Detectors in ATLAS

Sep 26, 2006, 5:10 PM
Valencia, Spain

Valencia, Spain

IFIC – Instituto de Fisica Corpuscular Edificio Institutos de Investgación Apartado de Correos 22085 E-46071 València SPAIN


Trevor Vickey (Univ. of Wisconsin, Madison, Department of Physics)


I present an overview of a read-out driver (ROD) for silicon detectors in the ATLAS experiment at the Large Hadron Collider (LHC). Two silicon-based ATLAS tracking systems, referred to as the Pixel Detector and the Semiconductor Tracker (SCT), are controlled and read-out using a common 9U VME board. A hybrid design of Field Programmable Gate Arrays (FPGAs) and Digital Signal Processors (DSPs) has allowed the Silicon ROD to meet the challenges of format error-counting and event trapping without interfering in the construction and transmission of event fragments to the next level in the read-out system. Performance of the ROD during detector assembly, calibrations and cosmic-ray data-taking are also discussed.


The ATLAS experiment is a general-purpose detector centered around one of the LHC
$pp$ collision points. Two major ATLAS detector subsystems lie closest to the
interaction point--the Pixel detector, comprised of more than $8.0 \times 10^7$
channels (1744 modules), surrounded by the SCT, itself containing more than $6.2 \times 10^6$ channels (4088 modules); both are essential for providing the tracking
information used to tag secondary vertexes from b-hadron decays. The ROD is a 9U VME
board common between both of these detector systems and designed to meet the
formidable challenge of module configuration and read-out, trigger distribution and
event fragment construction.

Each VME board is responsible for the configuration and read-out of up to 48 SCT or
32 Pixel modules. A hybrid architecture of FPGAs and DSPs allow the ROD maximum
versatility during physics-running and calibrations. The FPGAs are dedicated to
performing ROD setup and module configuration in addition to the formatting, building
and routing of events. A single Master'' and fourSlave'' DSPs reside on the
board and are utilized for the control and coordination of on-ROD operations, as well
as performing high-level tasks such as data monitoring and module calibration. Once
configured, the ROD FPGAs handle the event data path to Level-Two without further
assistance from the DSPs.

The Master DSP (MDSP) controls and coordinates ROD operations via a register bank
connected to one of its external memory interfaces (EMIF). Two additional EMIFs are
utilized for storing additional program code and general data (\emph{ e.g.}, module
configuration data). A re-programmable boot ROM is attached to the fourth EMIF
allowing the MDSP to load initial code upon start-up. The MDSP's host port interface
allows a host CPU continuous access to its internal memory banks.

The four Slave DSPs (SDSPs) are used for error counting as well as event capture and
histogramming. One EMIF of each SDSP is connected to a separate pipeline in the
Router FPGA, thus allowing events to be transferred independently to any SDSP. SDSP
external memory is used to store event histograms. The full memory range of the four
SDSPs are available to the MDSP through registers attached the the SDSP host port

ROD calibration mode is utilized for running a sequence of module communication and
functionality tests that optimize optical receiver settings, verify the function of
BC and Level-1 ID counters, set charge injection timing and measure gain offset and
noise. Calibration mode has been used extensively during detector assembly--an
individual silicon module is thoroughly tested prior to being mounted on a barrel or
a disk.

With the advent of SCT commissioning using cosmic-rays, the optimization of ROD
software and firmware will continue in concert with working to meet the challenges of
Simple Link Interface (S-LINK) readout during physics-running and multi-ROD operation.

Primary author

Trevor Vickey (Univ. of Wisconsin, Madison, Department of Physics)

Presentation materials