A situation in which the TriggerCandidate fragment in the TriggerRecord is empty

I don't know if the trigger repo is the best place for this Issue, nor do I know if what I've seen is a feature or a problem, but I wanted to share what I've seen.

In a somewhat contrived situation that I stumbled upon accidentally, I see TRs that have empty TC fragments. I saw this when using the most recent RandomTriggerCandidateMaker code and when using the MLT readout window map. The accidental choice that I made was to set the readout window in the MLT readout map to be smaller than what the RTCM uses naturally.

Here are the steps to demonstrate what I've seen:

source /cvmfs/dunedaq.opensciencegrid.org/setup_dunedaq.sh
setup_dbt latest
dbt-create -n NAFD24-02-09 09FebFDDevEmptyTCDemo
cd 09FebFDDevEmptyTCDemo/sourcecode
git clone https://github.com/DUNE-DAQ/daqsystemtest.git -b develop
git clone https://github.com/DUNE-DAQ/hdf5libs.git -b kbiery/empty_tcfrag_fix
cd ..

dbt-workarea-env
dbt-build -j 20
dbt-workarea-env

mkdir rundir
cd rundir

cat <<EOF1 > daqconf.json
{
  "boot": {
    "use_connectivity_service": true,
    "start_connectivity_service": true,
    "connectivity_service_host": "localhost",
    "connectivity_service_port": 15432
  }, 
  "daq_common": {
    "data_rate_slowdown_factor": 1
  },
  "detector": {
    "clock_speed_hz": 62500000
  },
  "readout": {
    "use_fake_cards": true,
    "default_data_file": "asset://?label=WIBEth&subsystem=readout"
  },
  "trigger": {
    "use_random_maker": true,
    "rtcm_timestamp_method": "kTimeSync",
    "rtcm_time_distribution": "kUniform",
    "rtcm_trigger_interval_ticks": 62500000,
    "mlt_use_readout_map": true,
    "mlt_td_readout_map": [
      {
          "candidate_type": 4,
          "time_before": 100,
          "time_after": 200
      }
    ]
  },
  "hsi": {
    "use_fake_hsi": false,    
    "use_timing_hsi": false,    
    "random_trigger_rate_hz": 1.0
  }
}
EOF1

cat <<EOF2 > dro_map.json
[
    {
        "src_id": 100,
        "geo_id": {
            "det_id": 3,
            "crate_id": 1,
            "slot_id": 0,
            "stream_id": 0
        },
        "kind": "eth",
        "parameters": {
            "protocol": "udp",
            "mode": "fix_rate",
            "rx_iface": 0,
            "rx_host": "localhost",
            "rx_pcie_dev": "0000:00:00.0",
            "rx_mac": "00:00:00:00:00:00",
            "rx_ip": "0.0.0.0",
            "tx_host": "localhost",
            "tx_mac": "00:00:00:00:00:00",
            "tx_ip": "0.0.0.0"
        }
    },
    {
        "src_id": 101,
        "geo_id": {
            "det_id": 3,
            "crate_id": 1,
            "slot_id": 0,
            "stream_id": 1
        },
        "kind": "eth",
        "parameters": {
            "protocol": "udp",
            "mode": "fix_rate",
            "rx_iface": 0,
            "rx_host": "localhost",
            "rx_pcie_dev": "0000:00:00.0",
            "rx_mac": "00:00:00:00:00:00",
            "rx_ip": "0.0.0.0",
            "tx_host": "localhost",
            "tx_mac": "00:00:00:00:00:00",
            "tx_ip": "0.0.0.0"
        }
    }
]
EOF2

fddaqconf_gen -c ./daqconf.json --detector-readout-map-file ./dro_map.json mdapp_wibeth_rtcm_mltrw

nanorc --partition-number 2 mdapp_wibeth_rtcm_mltrw ${USER}-test boot conf start_run 101 wait 20 stop_run scrap terminate

HDF5LIBS_TestDumpRecord swtest_run000101_0000_*.hdf5

When you run the last step (the TRDump), you'll see that the TC fragments are empty.

Reproduce the case using the supplied daqconf.json, dro_map.json, RandomTriggerCandidateMaker, and MLT readout map settings, then inspect the trigger record path and HDF5LIBS_TestDumpRecord output. Done means the demonstrated configuration no longer produces TriggerRecords with empty TriggerCandidate fragments, with a regression test covering the smaller readout window.