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A large ion collider experiment (ALICE) experiment focuses on the study of the quark-gluon plasma as a product of heavy-ion collisions at the CERN large hadron collider (LHC). During the long shutdown 2 of the LHC in 2019–2020, a major upgrade is underway in order to cope with a hundredfold input data rate increase with peaks of up to 3.5 TB/s. Thi...
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... Memory Layout: DMA transfers are performed using DMA channel buffers, made up of shared memory, and are comprised of Superpages. A Superpage (usually 1 MiB) is the granularity level on which the driver and the cards communicate. Each Superpage contains DMA pages, which have a variable size of up to 8 KiB, even within the same Superpage (see Fig. 5). Every DMA page includes a header followed by the payload. With regard to its DMA functionality, the driver is agnostic to the content and structure of a ...
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... Simply known as readout, the detector readout software [7], written in modern C++, is in charge of controlling the readout cards (CRU and C-RORC) and managing the memory buffers into which the DMA transfers are performed. Interaction with the readout cards is done via the ReadoutCard library [8], a C++ high level interface based on the Portable Driver Architecture. Once the data is in the host memory, readout aggregates the data from multiple links, performs a set of checks, formats the outgoing data and slices it up into time-based data units that are then sent to the data distribution software. ...
ALICE (A Large Ion Collider Experiment) has undertaken a major upgrade during the LHC Long Shutdown 2. The increase in the detector data rates led to a hundredfold increase in the input raw data, up to 3.5 TB/s. To cope with it, a new common Online and Offline computing system, called O², has been developed and put in production. The O²/FLP (First Level Processor) system, successor of the ALICE DAQ system, implements the critical functions of detector readout, data quality control and operational services running in the CR1 data centre at the experimental site. Data from the 15 ALICE subdetectors are read out via 8000 optical links by 500 custom PCIe cards hosted in 200 nodes. It addresses novel challenges such as the continuous readout of the TPC detector while keeping compatibility with legacy detector front-end electronics. This paper discusses the final architecture and design of the O²/FLP system and provides an overview of all its components, both hardware and software. It presents the selection process for the FLP nodes, the different commissioning steps and the main accomplishments so far. It will conclude with the challenges that lie ahead and how they will be addressed.
... PDA also provides a user space library in C [101] which supports PCIe device enumeration and provides a handle to PCI devices. The readout software includes the readout program and the readoutCard library [102] which orchestrate the simultaneous data transfers from the GBT links to the FLP memory as shown in Fig. 91. The transfer of data to the EPN farm is handled by the O 2 data distribution (see Sec. 5.3). ...
... Detectors that require latency-critical trigger signals receive these trigger signals additionally on a direct path from the CTS to the detector front-ends on GBT links. Legacy detectors not supporting continuous readout are read out via C-RORC readout cards [7,102] and require a hardware trigger signal to initiate the readout. They receive the clock and trigger signals via the legacy TTC system [4]. ...
A Large Ion Collider Experiment (ALICE) has been conceived and constructed as a heavy-ion experiment at the LHC. During LHC Runs 1 and 2, it has produced a wide range of physics results using all collision systems available at the LHC. In order to best exploit new physics opportunities opening up with the upgraded LHC and new detector technologies, the experiment has undergone a major upgrade during the LHC Long Shutdown 2 (2019-2022). This comprises the move to continuous readout, the complete overhaul of core detectors, as well as a new online event processing farm with a redesigned online-offline software framework. These improvements will allow to record Pb-Pb collisions at rates up to 50 kHz, while ensuring sensitivity for signals without a triggerable signature.
A Large Ion Collider Experiment (ALICE) has been conceived and constructed as a heavy-ion experiment at the LHC. During LHC Runs 1 and 2, it has produced a wide range of physics results using all collision systems available at the LHC. In order to best exploit new physics opportunities opening up with the upgraded LHC and new detector technologies, the experiment has undergone a major upgrade during the LHC Long Shutdown 2 (2019–2022). This comprises the move to continuous readout, the complete overhaul of core detectors, as well as a new online event processing farm with a redesigned online-offline software framework. These improvements will allow to record Pb-Pb collisions at rates up to 50 kHz, while ensuring sensitivity for signals without a triggerable signature.
As from the run 3 of CERN LHC scheduled in 2022, the upgraded ALICE experiment will use a Common Readout Unit (CRU) at the heart of the data acquisition system. The CRU, based on the PCIe40 hardware designed for LHCb, is a common interface between 3 main sub-systems: the front-end, the computing system, and the trigger and timing system. The 475 CRUs will interface 10 different sub-detectors and reduce the total data throughput from 3.5 TB/s to 635 GB/s. The ALICE common firmware framework supports data taking in continuous and triggered mode and forwards clock, trigger and slow control to the front-end electronics. In this paper, the architecture and the data-flow performance are presented.
