Trigger

(Last updated July 2023, MiR + AS)

The trigger package contains the modules that make up the DUNE FD DAQ trigger system. Implementations of the physics algorithms that produce data selection objects (trigger activity and trigger candidates) live in the triggeralgs package. Also, the scripts that generate the trigger application configuration live in daqconf.

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  The main goal of the trigger is to extract information from data to form Trigger Decisions. Additionally, in conjunction with the Data Filter, the aim is to reduce the total data volume from the four planned DUNE modules to be in line with the DUNE requirements for trigger acceptance and efficiency for various physics signals.

Table of content

1. Overview
   1. More details (of trigger functionality)
2. Structure
   1. Terminology
      1. Main objects
      2. Modules-Makers
      3. Modules-Other
3. Flow
   1. Flow - detailed
4. Links to other repositories
   1. Triggeralgs
   2. Trgdataformats
   3. Daqconf
5. Running
   1. online
   2. offline
6. Development
7. Other

Overview

More details (of trigger functionality):

• Identify clusters of electronic signals indicating potentially interesting physics activity in a module and store those in Trigger Primitive data objects.

• Handle multiple trigger sources, including TPC, PDS, calibration sources, beam information, and “external” information such as SNB notifications from adjacent DUNE modules or other experiments. Merging of readout windows for multiple coincident triggers, and explicit coincidence requirements (if desired) must be possible.

• Provide triggers such as random or pulsed triggers, and support pre-scaling of all triggers (most likely to be used with low-threshold or high-rate triggers).

• Have a latency that is small compared to the resident time of data in the Readout buffers.

• Allow offline measurements of trigger efficiency and reconstruction of the decision path that went into generating a Trigger Record.

• Provide the ability to measure any trigger-related dead time, and provide operational monitoring information about rates of different trigger types.

• Not rely on external inputs (but these are supported (eg calibration)).

All in all, the trigger is not just about selecting data, but rather selecting data in real time, i.e. taking decisions continuously, within an agreed latency and with limited computing resources compared to what can be done offline.

Trigger's position relative to DAQ:

As can be seen, the trigger lies in the heart of DUNE DAQ, receiving multiple inputs, creating and forwarding trigger decisions, while also responding to data requests.

Structure

The trigger is designed hierarchically. The minimal (extremely simplified) flow:

  The channel-level information in the form of Trigger Primitives is merged locally (at the scale of one TDAQ unit, such as an APA or CRP) into a cluster representing some type of Trigger Activity. Multiple Trigger Activity outputs can then be merged into a single Trigger Candidate that may include information spanning multiple TDAQ units or multiple slices of time (say, many APAs or many seconds) for a single system. Finally, multiple Trigger Candidates can be merged across systems (e.g. TPC and PDS) in the MLT.

Terminology:

Main objects:

• Trigger Primitive (TP): The Simplest signal waveform representation (wire hit). These are generated using hit finding algorithms in the readout subsystem.
• Trigger Activity (TA): Cluster of hit(s) (TP(s)) that have been deemed fit to be sent up to the next level in the trigger hierarchy. Typically these will be tracks/showers or other outstanding physics activity within the box (sub-detector).
• Trigger Candidate (TC): Cluster of TAs across all sub-detectors.
• Trigger Decision (TD): A trigger request issued by Module Level Trigger (MLT) to the Data Flow Orchestrator (DFO) in order to request the raw data of the relevant detector channels over specified time windows from the readout subsystem that should be permanently stored for later analysis.
• Trigger Record (TR): An object in a stored file, containing the raw data, TPs, TAs, and TCs that have led to its construction.

Modules-Makers:

• Trigger Activity Maker (TAM): A general module in charge of processing the incoming stream of TPs and issuing a localised activity trigger at the granularity of single APA/CRPs (and PDS detector units in the future). TAM have with them associated an algorithm, which attempts to search the incoming TP stream for interesting physics activity. The TAs that the TAM produces are sent to the TCM.
• Trigger Candidate Maker (TCM): In analogy to the TAM, which identifies clusters of TPs representing activity across many wire channels, the TCM identifies clusters of TAs across many APAs/CRPs. As an example, consider a cathode crossing muon in ProtoDUNE, that generates a track on two opposite facing APAs. Should we want to trigger on this, the TCM might wait for the two corresponding tracks on the opposite APAs before issuing a TC to the Module Level Trigger.
• Module Level Trigger (MLT): What you might imagine to be called the “TDMaker” at this point, is in fact the ‘edge’ of the trigger system, and we call it the Module Level Trigger. As its name suggests, it is in charge of sending TDs to dataflow orchestrator for raw data contained within an entire DUNE FD module.

Modules-Other:

• TPChannelFilter: Filters out collection or induction TPs from its input TPSets and passes them on. One can filter out TPs based on their offline channel number. Useful for testing on the VDCB, where one might want to only present collection TPs to the TAM when searching for tracks. It can also filter out noisy channels.
• Zipper: A general module in charge of combining inputs from multiple streams and outputting them - time ordered - in a single queue to the following module (these require time ordered objects). ‘Late’ objects are deemed ‘tardy’ according to their timestamps and dropped, since it is impossible to maintain time ordering when objects of an earlier timestamp than those that have already been sent arrive at the zipper.
• Tee: DUNE DAQ has no inbuilt functionality for making copies of objects, so this module is a workaround for that. Each copy can be sent to a different module onward.
• Buffer: We generally want to store the TPs, TAs, and TCs that led to stored Trigger Records (TRs) inside those TRs. The buffers service this ambition. We have TPBuffers, TABuffers, and TCBuffers. They receive directly from the relevant Tee modules, as described above. Data requests are made to these buffers when a trigger decision is made (as well as to the raw data buffers in readout).

Flow

A more realistic (still simplified) flow through the trigger application:

  The diagram above shows the DAQModules and connections in an example trigger app. Blue rounded rectangles are DAQModules in the app, while red rectangles are external inputs, blue rectangles are external outputs; and coloured ellipses are external connections producing requests. Each DAQModule is labelled by its plugin type, and edges show the type of data that flows along the corresponding queue. There are two main sets of inputs: trigger primitives - packaged as TPSets - from readout, seen at the top of the image; and HSI events from the hardware signals interface, seen towards the bottom. Eventually, each of these inputs are processed into Trigger Candidates (TCs), which are fed to the Module Level Trigger, which issues trigger requests to the data flow orchestrator.

Flow - detailed:

Following one TPSet stream from upstream to downstream:

• The first module is the TPChannelFilter, which filters out collection or induction TPs from its input TPSets and passes them on. There is always one TPChannelFilter per sub-detector (there can, of course, be multiple sub-detectors - think APAs).
• Next we need to send the TPSets downstream to two different places. Firstly, to the activity makers (sometimes called algorithms) that will make trigger activities (TAs), and secondly to the buffer that holds TPs to be sent as a fragment in response to a data request from the data flow subsystem. Unfortunately the DAQ framework doesn’t provide a facility to do this copy, so we have to do it ourselves via the TPSetTee module (which is a template specialization of the Tee<T> class).
• Following that is the Trigger Activity Maker (a specialization of the Trigger Generic Maker class) which handles passing the TPs from the TPSets to a (configurable) algorithm that makes TAs out of them, if conditions are met. The algorithm implements a function that takes a single Trigger Primitive and adds any TAs created at that step into an output vector. TAM guarantees that calls to the algorithm present the Trigger Primitives in time order (by start time). To achieve this, the TAM buffers its inputs until it knows it has got all of the TPSets for time T that it will get, then sorts the TPs from those TPSets before passing them to the TAM algorithm. The algorithm is not required to produce its outputs in any particular order; instead the TAM buffers the outputs from the algorithm and sends them out in order. If the algorithm outputs a TA with timestamp less than the last timestamp sent out by the TAM, that output is deemed tardy and dropped with a warning message. Each TAM sees the TPs from one APA.
• Next in the chain is the TASetTee - which is analogous to TPSetTee - with the only difference being that it works with TAs instead of TPSets.
• The TAZipper module zips data (think merging) across all sub-detectors. It takes multiple input streams of TAs - each of which is time-ordered - buffers them, and outputs them in time-order. This is a non-trivial operation because the different streams might not be exactly synchronized due to network or processing delays upstream. The zipper has a configurable timeout after which it will send TAs downstream even if it hasn’t seen a TA from every stream. After this, it’s possible for the zipper to move on and continue emitting TAs with later times. If a new input arrives with timestamp earlier than the latest sent time, it’s impossible to send that input while maintaining time-ordering of the output. The input is deemed “tardy” and it’s dropped with a warning message.
• The TASetTee and Trigger Candidate Maker are analogous to the TPSetTee and TriggerActivityMaker respectively, just with TASets as inputs. Thanks to the TAZipper upstream, the Trigger Candidate Maker is able to operate with activities from different sub-detectors (think APAs), continuing the 'activity hierarchy'.
• The TCs made by the TCM are sent to the Module Level Trigger, which is responsible for sending the final Trigger Decision to the data flow subsystem (specifically to the data flow orchestrator). In addition to the TCs formed from TAs/TPs, there is an input stream to the MLT from the hardware signals interface (HSI). The stream sent to the trigger subsystem from the HSI consists of HSIEvents. These enter the Timing Trigger Candidate Maker. This module converts HSIEvents to TCs which are passed to the MLT.
• TPBuffer, TABuffer and TCBuffer (collectively, TXBuffer) buffer TPs/TAs/TCs and respond to data requests from the dataflow system. This means that the offline data file contains the TPs/TAs/TCs that were created in some time window around the trigger timestamp. The TXBuffer classes are plugins in the trigger package, but the real work is done by code borrowed from datahandlinglibs, in order to share the implementation of buffering and responding to data requests.
• The Module Level Trigger takes TCs from one or more streams and uses them to construct trigger decisions (TDs) that are sent to the dataflow subsystem. In the simplest case, the MLT just makes one TD for each TC it receives. However, MLT is capable of merging TCs whose readout windows overlap (defined by start and end times of the incoming TCs), and also has the option to trigger on coincidence(s) of selected TCs. The MLT can be in paused, inhibited, or enabled state. “Paused” means a human has paused triggers for some reason (likely at a test beam, unlikely in DUNE FD), while “inhibited” means the data flow subsystem has indicated that it can’t receive any more triggers (presumably because it can’t keep up with the trigger rate, although that’s not assumed anywhere in the MLT). In both these cases, no trigger decisions are sent to the DFO.

  It's important to keep in mind that the set-up (configuration) can vary widely. We can have one or multiple sub-detectors (APAs / CRPs) AND we can have multiple makers (e.g. separate TAM for PDS and TPC systems).

The general numbers are:

• TPChannelFilter: 1 per link (link here represents sub-detector (APA/CRP))
• TPSetTee: 1 per link
• TriggerActivityMaker: 1 (or more) per link
• TASetTee: 1 per link
• TAZipper: 1 per TAM algorithm
• TriggerCandidateMaker: 1 (or more) per link
• TCTee: 1 per TCM
• TPBuffer: 1 per TPSetTee
• TABuffer: 1 per TASetTee
• TCBuffer: 1
• MLTModule: 1 per application
• (optional)TimmingTriggerCandidateMaker: 1

Links to other repositories

Triggeralgs (link)

The triggeralgs package contains implementations of the algorithms that produce TAs from TPs and TCs from TAs. The idea of keeping these in their own package (instead of trigger) is to allow the algorithms to be used in the offline software to simulate the effect of the trigger system, where probably the only things they care about are efficiency at very low energies and whatever we do about not reading out the whole detector for every event, which will certainly involve not reading out all APAs/CRPs, and may also include more aggressive ROI finding. Keeping triggeralgs separate from trigger means that the former package doesn’t need to depend on anything from the DAQ software, and so could just be built as part of the offline software. Loading triggeralgs algorithms dynamically as plugins in the DAQ is done in a complicated way: triggeralgs doesn’t depend on any plugin library, so instead we manually make plugins in the trigger package for each of the algorithms in triggeralgs, like this: TAMakerPrescaleAlgorithm.cpp.

Trgdataformats (link)

The approach used by DUNE DAQ for saving fragments to disk is designed for raw data that comes off of hardware, which is always a stream of contiguous bytes, with a well-defined meaning for each byte. The objects in the trigger system, on the other hand, are defined as C++ structures, which could potentially be expressed in different ways in memory (eg on big-endian or little-endian systems), and are not in general contiguous (they might have pointers to data on the heap, as when you have a std::vector member). What this means for the trigger is that if we want to store trigger primitives/activities/candidates in fragments (for debugging, for understanding the trigger system, for passing to the data filter, or for offline analysis), we have to make a representation of the class that is contiguous in memory, with data at specified byte positions. This happens in trgdataformats using overlays, explained here: trigger data objects.

Daqconf (link)

The daqconf repository contains tools for generating DAQ system configurations. It generates DAQ system configurations with different characteristics based on the configuration file and command-line parameters given to it. This includes configuration for the trigger application. So every input that needs to be configurable is handled here and passed to the trigger app. Additionally, the links (input/output connections between modules) are also defined here.

Running

online

The instructions for running with real hardware change often. Please follow:

• Trigger system introduction document: DocDB #28497 (also contains many useful links!)
• Run control (CERN): link
• DUNE DAQ Prototype (CERN): link
• Daqconf wiki: link

offline

Trigger replay app replay_tp_to_chain: A tool for running the trigger application in isolation from the rest of the DUNE DAQ apps. It accepts input file(s) that are simple .txt, containing TPs; and runs your configured algorithm over them. These could be real streamed TPs (from the cold-box for example) or simulated ones (LArSoft).

• python -m trigger.replay_tp_to_chain: runs the configuration generation code.
• -s X slows down the input by a factor X (by decreasing the clock rate by that factor) which is useful when outputting large logs/debugging information for example.
• --trigger-activity-plugin specifies the name of the TAM you would like to use.
• Similarly --trigger-candidate-plugin identifies the TCM.
• --trigger-activity-config provides a dictionary, which maps the configuration for your specified TAM, triggering thresholds etc. This can be done for the TCM too.
• -l specifies the number of times you would like to play the data file through the system.
• Finally, --input-file points to your input file of TPs, which have the standard format:

time start	time over threshold	time peak	channel	adc integral	adc peak	det id	type

Few example files are available at /nfs/rscratch/trigger/tp_files at CERN:

• 1000_electron_events.txt: simulated electron events
• tp_dataset_run020472_2s.txt: real TPs taken from March 2023 Vertical Drift ColdBox, 2 seconds
• tp_dataset_run020472_60s.txt: real TPs taken from March 2023 Vertical Drift ColdBox, 60 seconds
• pds_tps_60s.txt: real TPs from the PDS system

Example command:

python -m trigger.replay_tp_to_chain -s 10 --trigger-activity-plugin TAMakerHorizontalMuonAlgorithm --trigger-activity-config ‘dict(adjacency_threshold=100, window_length=10000, adj_tolerance=20)‘ --trigger-candidate-plugin TCMakerHorizontalMuonAlgorithm --trigger-activity-config ‘dict(adjacency_threshold=100, window_length=10000, adj_tolerance=20)‘ -l 1 --input-file $TPDATA/tp_dataset_run020472_2s.txt json

Development

• Development workflow
• Setting up DUNE DAQ development area
• Writing trigger algorithm
• DAQ buildtools
• Coding styleguide

For trigger code development, please:

• Follow the styleguide linked above.
• Never push directly to the develop branch. Create a branch (name should contain an easily recognisable name and reflect the purpose of the feature/fix, e.g. name/new_feature.) and make a pull request to the appropriate branch. At least one reviewer is required (more for big changes). General rule of thumb: don't merge your own PR.
• Always use integration tests. A selection is available at daq-systemtest integration tests. As a minimum, the minimal_system_test, fake_data_producer and 3ru_3df_multirun tests should be run (the more the better of course). Some tests require more powerful machines (available at np04).
• No warnings when building.
• clang formatting: there is an inbuilt script available (from dbt) to apply Clang-Format code style: dbt-clang-format.sh. Run without arguments for usage information.

Other