Abstract
The new LHCb Vertex Locator (VELO) for LHCb, comprising a new pixel detector and readout electronics, will be installed in 2021 for data taking in Run 3 at the LHC. The electronics centers around the “VeloPix” ASIC at the front-end operating in a trigger-less readout at 40MHz. A custom serializer, called gigabit wireline transmitter (GWT), and associated custom protocol have been designed for the VeloPix. The GWT data are sent from the serializers of the VeloPix at a line rate of 5.12 Gb/s, reaching a total data rate of 2–3 Tb/s for the full VELO detector. Data are sent over 300-m optic-fiber links to the control and readout electronics cards for deserialization and processing in Intel Arria 10 FPGAs. Because of the VeloPix trigger-less design, latency variances up to 12 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> can occur between adjacent datagrams. It is therefore essential to buffer and synchronize the data in firmware prior to onward propagation or suffer a huge CPU-processing penalty. This article will describe the architecture of the readout firmware in detail with focus given to the resynchronization mechanism and techniques for cauterization. Issues found during readout commissioning, and scaling resource utilization, along with the their solutions, will be illustrated. The latest results of the firmware data-processing chain can be presented as well as the verification procedures employed in simulation. Challenges for the next generation of the detector will also be presented with ideas for a readout processing solution.
Highlights
T HIS article describes the readout architecture of the LHCb vertex locator (VELO) [1]–[3] currently being constructed and commissioned for operation for LHC Run 3 in 2022
The introduction outlines the set of requirements of the Vertex Locator (VELO) firmware, namely, 1) handling the VeloPix custom gigabit wireline transmitter (GWT) protocol; 2) reordering of the data fragments in time; and 3) processing the SuperPixel data content
The outlier in the change of resources is the increase in digital signal processors (DSPs), which increase by a factor of 11.2×
Summary
T HIS article describes the readout architecture of the LHCb vertex locator (VELO) [1]–[3] currently being constructed and commissioned for operation for LHC Run 3 in 2022. PEAK DATA RATES CORRESPONDING TO THE VELOPIX ASIC WITH THE HIGHEST EXPECTED OCCUPANCY, AND THE RESULTANT BANDWIDTHS of signal amplitude) in a data-driven mode. This means that hits above a configurable threshold produce data packets to be transmitted (and those below threshold are suppressed and yield no data). The chip is designed with a columnar readout path, where data fragments traverse the length of the column from their origin, are subsequently assembled at the endof-column logic, and routed toward the center for transmission.
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