Speaker
Description
Timing and control firmware was developed to operate a vertical slice of the CMS high-granularity calorimeter front-end and back-end systems at beam tests, in the absence of a full-fledged system. It provides various trigger sources (software, regular, random, external), throttling mechanisms and a programmable sequencer of fast commands. A data capture block for local readout of the outgoing event data through an IPBus interface complements this development. Such integration facilitates the development of standalone BE systems without specialized timing/trigger distribution or DAQ hardware. Modular design of the firmware and software enables easier adaptation for other detector subsystems.
Summary (500 words)
The CMS experiment is developing the TCDS2 (Timing and Control Distribution System 2) and the next generation of SlinkRocket-based data acquisition (DAQ) systems for HL-LHC. This system will distribute LHC clock and bunch-synchronous commands to the detector electronics and record event data. The initial release of this system does not yet support all the features, e.g. the ability to run a calibration sequence. Emulator firmware was developed as part of the back-end (BE) firmware for the High Granularity Calorimeter (HGCAL) beam-test campaign. This TCDS2 emulator was flanked by a highly versatile fast control (FC) distribution chain for the HGCAL BE FPGAs and an external trigger generation system (Figure 1). The external trigger system consists of lpGBT-based scintillator signal sampler and firmware to calculate the trigger phase (0.78ns resolution). The TCDS2 emulator provides LHC-like clock-base, orbit synch signals and various fast commands to control BE and front-end (FE) systems. It consists of configurable trigger sources, which provide software-programmed, regularly spaced or randomly spaced triggers across an LHC orbit. They can also be combined to form complex trigger patterns to probe corner cases and stress BE. The trigger flow can be controlled by different throttle mechanisms, such as software, external, auto-throttle (to allow only N triggers out of M crossings) and detector-specific FE buffer emulation throttle. A flexible sequencer block is a key feature of the TCDS2 emulator, which can be programmed with an arbitrary sequence of fast commands, covering whole LHC orbit (using YAML), including multiple commands per bunch crossing. This has been central in executing calibration and front-end alignment sequences. The downstream encoder block creates detector-specific FC codes with priority encoding and adds additional flexibility, such as stretching incoming trigger requests to be repeated over sequential multiple bunch crossings, which allows capture of longer features of the detector signals, and debug and stress-test the electronics systems. The modular firmware design keeps the detector-specific and common blocks separate and can be easily adapted to other detector systems. The local readout consists of a large (256kB) URAM buffer to store a large event packet payload. It creates an event packet with the SlinkRocket format and loads one or more fragments up to 1022 words long into an output buffer connected to a slow-control interface. Event readout rates of about 5kHz have been achieved (~2kB packet), which is sufficient for standalone systems with low throughput requirements such as cosmic test stands. The local readout can be used with TCSD2 emulator’s auto-throttle mechanism to provide a controlled number of packets through the system and releasing the throttle after these have been read out, keeping readout synchronous across multiple local readout endpoints. These firmware and software developments have proved critically useful in HGCAL test beams and various lab test systems for different levels of system validation. They are also envisaged to be leveraged in developing the HGCAL single-cassette test stand, which will primarily look at pedestal data and low-rate cosmic muon triggers.
