Readout Firmware of the Vertex Locator for LHCb Run 3 and Beyond

• Published in: IEEE transactions on nuclear science Vol. 68; no. 10; pp. 2472 - 2479
• Main Authors: Hennessy, Karol, Prieto, Antonio Fernandez, Regueiro, Pablo Vazquez, Buytaert, Jan, Van Beuzekom, Martin, Cid, Edgar Lemos, Eklund, Lars, de Bruyn, Kristof, Naik, Sneha, Schiller, Manuel, Murray, Donal, Leflat, Alexander, Bassi, Giovanni, Punzi, Giovanni, Lazzari, Federico, Morello, Michael J., Garcia, Oscar Boente, Torreira, Abraham Gallas, Plana, Beatriz Garcia, Bowcock, Themis, Dettori, Francesco, Dreimanis, Karlis, Lima, Vinicius Franco, Hutchcroft, David, Rinnert, Kurt, Shears, Tara, Augusto, Oscar, Coco, Victor, Collins, Paula, Evans, Tim, Ferro-Luzzi, Massi, Schindler, Heinrich, Akiba, Kazu, Occo, Elena Dall', Graz, Cristina Sanchez, Hulsbergen, Wouter, Hynds, Daniel, Kostiuk, Igor, Merk, Marcel, Snoch, Aleksandra, Bobulska, Dana Seman, Borghi, Silvia, de Capua, Stefano, Dutta, Deepanwita, Gersabeck, Marco, Parkes, Chris, Svihra, Peter, Williams, Mark, Bogdanova, Galina, Volkov, Vladimir, Kopciewicz, Pawel, Majewski, Maciej, Oblakowska-Mucha, Agnieszka, Rachwal, Bartlomej, Szumlak, Tomasz, Garcia, Lucas Meyer, Marinho, Franciole, Mendes, Larissa Helena, Nasteva, Irina, Otalora, Juan, Rodrigues, Gabriel, Velthuis, Jaap, Jalocha, Pawel, John, Malcolm, Jurik, Nathan, Scantlebury-Smead, Luke, Back, John, Gershon, Tim, Latham, Tom, Morris, Andrew
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-10-2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Acidity; Bandwidth; DAQ; Data acquisition; Data processing; Decoding; Detectors; Electronics; Firmware; Large Hadron Collider; Latency; LHCb; Optical fiber communication; readout; Resource utilization; Sensors; Sodium channels; Timing; vertex locator (VELO)
• ISSN: 0018-9499; 1558-1578
• DOI: 10.1109/TNS.2021.3085018

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> <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.