`filewriter`: Neutron event data (`raw_data_1/detector_1_events`)

filewriter のエントリポイントから始め、既存の出力を raw_data_1/detector_1_events にある NXevent_data グループと比較します。event_aggregator の動作を読み、event_time_bins、基準時刻の順序、イベントの順序、veto フラグに関する疑問を解決します。必要なストリーミングイベントファイル形式と処理ルールについて合意し、実装されれば完了です。

The filewriter must be able to write out event-mode data.

This means the contents of the NXevent_data group in raw_data_1/detector_1_events

Questions

• What do we want to do with event_time_bins, which aren't meaningful in streaming system?
• Due to an underlying UDP connection from hardware, the streaming system cannot guarantee that frame N+1 will have a later reference_time than frame N. Do any consumers make assumptions about this?
  • This affects whether we can stream events to file directly, or whether we have to buffer, sort by reference time, and then write to file
• Does mantid have a dependency on event time-of-flights being ordered within a frame? Currently this sort is (optionally) done at event_aggregator level as multiple consumers benefit from improved performance with sorted events.

Potential differences from existing files

• We likely no longer need to apply a random event_time_offset_shift, as the new electronics has a much higher time resolution than the old DAE electronics. See https://github.com/ISISComputingGroup/DataStreaming/issues/22 .
• We want to be able to write the veto flags for each frame alongside the event data, to enable downstream consumers to retroactively enable or disable a veto if it chooses:
  • active_vetos: the veto signals that were actually active for a given frame
  • enabled_vetos: the vetoes that were enabled in IBEX at the time of data acquisition
  • By default downstream consumers will want to mask any events where active_vetos & enabled_vetos != 0.
  • If adding this logic is problematic for Mantid, we could (optionally) drop the frames at filewriter level instead - at the cost of reducing flexibility and reducing diagnostics we have access to.