McStas Readout Master for ESS detectors

Components and tools linking McStas 3.3+ ray-tracing neutron simulations to the ESS data pipeline via the Event Formation Unit (EFU).

Simulated readout records are collected to HDF5 files while the simulation runs, combined across repeated runs or scan points, and replayed to EFUs afterwards, statistically correctly — the data-acquisition stack does not need to be running (or reachable) during the simulation.

Documentation

Guides, per-component parameter references, CLI documentation, and the C/C++ API reference are published at

https://mcdotstar.github.io/mcstas-readout-master/

To build the site locally (requires Doxygen):

cmake -S . -B build-docs -DREADOUT_DOCS_ONLY=ON
cmake --build build-docs --target docs
# open build-docs/docs/html/index.html

Quickstart

1. Install

git clone https://github.com/mcdotstar/mcstas-readout-master.git
cmake -S mcstas-readout-master -B mcstas-readout-master-build -DCMAKE_INSTALL_PREFIX=~/.local
cmake --build mcstas-readout-master-build --target install

This installs libreadout, the readout-config, readout-combine, and readout-replay tools, and the McStas component files.

2. Collect

Add a Collector* component matching your detector electronics (CAEN, CDT, VMM3, BM0, BM2, BMI) to the end of your instrument's TRACE section. Identifying values are read by name from particle variables (typically USER_VARS set in an EXTEND block):

TRACE
  ...
  SEARCH SHELL "readout-config --show compdir"
  COMPONENT collect = CollectorCAEN(
    ring="ring_id", tube="tube_id", a_name="left", b_name="right",
    filename="run", dataset_name="caen_bank0")
  AT (0, 0, 0) ABSOLUTE

Each run produces a cue-based HDF5 file; several collectors can share one file, each writing its own named group.

3. Combine

readout-combine validate run_*.h5
readout-combine append      --output merged.h5 run_a.h5 run_b.h5   # identical parameters
readout-combine concatenate --output scan.h5   point_*.h5          # scan points

4. Replay

readout-replay --time 2.0 --seed 42 --addr my-efu.example.org --port 9000 scan.h5

Replay steps through the stored points, publishes each point's parameters, draws n ~ Poisson(w * counting_time) events per stored readout, and sends them to EFUs resolved from explicit configuration, file-embedded attributes, or the command-line defaults — in that order. See the CLI reference for all options.

Legacy runtime streaming

The original per-ray streaming components remain available for use cases where the EFU runs alongside the simulation: ReadoutCAEN makes a Poisson-distributed Monte Carlo choice per traced neutron and send packets immediately, and ReadoutDiscreteCAEN sends an exact number of weighted-sampled events at the end of the run. Their parameters are documented on the site and in the component headers (mcdoc-compatible).

MPI support

The Collector* components gather records to the master node, which writes one HDF5 file. For the streaming Readout* components, all nodes need network access to the EFU host.

Development

See DEVELOPMENT.md for the development-mode build (-DREADOUT_DEVELOPMENT_MODE=ON), test suites, and the reasoning behind the self-locating readout-config.

Use with McStas 3.2

The SEARCH SHELL automatic path modification used above requires McStas 3.3+. With McStas 3.2, copy the component files into one of the McStas component search directories and omit the SEARCH SHELL line.