udpPacketManager

udpPacketManager is a C library developed to handle reading and processing CEP packet streams from international Low Frequency Array (LOFAR) stations. It is used at the Irish LOFAR station (I-LOFAR, lofar.ie) for online data processing in conjunction with ILTDada for online data reduction to Stokes parameter science ready data products, or intermediate voltage formats for use with other software packages.

This library allows for entire, partial beamlet extraction and processing of LOFAR Central Processing (CEP) packet streams, re-aligning data to account for packet loss or misalignment on the first packet, to produce one of several data products, ranging from raw voltages (reordered or not) to a fully calibrated Stokes vector output.

The intended audience of this software is any observers, or users, that have raw CEP data produced by a LOFAR station and wish to convert it into a format usable by standard processing formats (DADA, GUPPI, etc.), or calibrated, science-ready data products (SigProc, HDF5, etc.).

Caveats & TODOs

While using the library, do be aware

• CEP packets that are recorded out of order may cause issues, the best way to handle them has not been determined, so they are currently dropped. This may cause some time-major formats to change shape (though at least in our experience, packets are more likely to be lost,
  no packets in 2022 were received out of order at IE613).

Future work should not break the existing load/process/output loop, and may consist of

• Creating a wrapper python library to allow for easer interfacing within python scripts rather than requiring a C program (pybind11?)
• Additional reader/writer format support
  • Adding support for the Zstandard seekable format
• Additional processing modes
• Additional metadata support (FITS frames?)

Requirements

In order to build and use the library, we require

• An x86-64 host system (ARM and other RISC based architechtures are currently untested/unsupported)
• A modern C and C++ compiler with at least OpenMP 4.5 and C++17 support
  • gcc-10/g++-10 used for development, clang-12 used in production
  • A range of tested gcc and clang releases can be found in the main.yml action file.
• A modern CMake version (>3.14, can be installed with pip)
  • A CMake compatible build system, such as make or ninja
  • git for cloning repositories
• csh, autoconf, libtool (for PSRDADA compile)

To avail of voltage calibration through dreamBeam, we additionally require

• A Python 3.8+ Interpreter available at compile and runtime

To automatically install the required dependencies on Debian-based systems, the following commands should suffice.

apt-get install git autoconf csh libtool make wget python3 python3-pip
pip install cmake

# Optional, for LLVM (clang) compilation
apt-get install clang libomp-dev libomp5

Our CMake configuration will automatically compile several dependencies (though they will not be installed to the system),

• FFTW3, an FFT library for channelisation of data
• GoogleTest, a testing framework
• HDF5, a data model
  • bitshuffle, a HDF5 compression filter
  • zlib, a HDF5 dependency
• PSRDADA, an astronomical ringbuffer implementation
• Zstandard, a compression library
• Python packages for calibration (and their dependencies, automatic installation available through CMake)
  • astropy
  • dreamBeam
  • lofarantpos

While we aim to have maximum support for common compilers, during the development of the library we have noted that the LLVM (clang) implementation of OpenMP, libomp, has significant performance benefits as compared to the GCC libgomp library bundled with GCC, especially for higher core count machines. As a result, we strongly recommend using a clang compiler when using the library for online processing of observations. Further details of this behaviour can be found in compilers.md.

Building and Installing the Library

Once the prerequisites are met, running the following set of commands is sufficient to build and install the library.

numThreads=8
mkdir build; cd build
cmake ..
cmake --build . -- -j${numThreads}

sudo cmake --install .

# Optional, run the test suite, after performing the install
ctest -V .

We provide these commands wrapped in a script at build.sh

Further Calibration Installation Notes

You may receive several errors from casacore regarding missing ephemeris, leap second catalogues, etc. when calibration is enabled. These can be resolved by following this help guide from the NRAO.

Docker Image

A Dockerfile is provided in src/docker/Dockerfile, and can be used to build a Docker container that contains the latest build of the software, or as a reference for installing the software on a minimal Ubuntu image.

Like all Docker containers, the docker2singularity image can be used to convert it into a singularity containter for a safer way to provide the software to users.

# From the root directory of this repo,
docker build -t udppacketmanager/latest . --file src/docker/Dockerfile
docker run -v /var/run/docker.sock:/var/run/docker.sock -v /tmp/test:/output --privileged -t --rm quay.io/singularity/docker2singularity udppacketmanager/latest

Usage

A quick-start guide on how to integrate the software in your project is provided in the integration readme file, and example implementations can be found in the provided CLIs, for example lofar_cli_stokes.c, or a simplified implementation can be found in example_processor.c.

Other documentation can be found in the docs/ folder.

Contributing

Issues and pull requests are welcomed through GitHub to report or resolve issues with the software, or if you wish to request/add additional functionality. All contributions are expected to follow the code of conduct laid out in the Contributor Covenant 2.0. Any contributions submitted will be licensed under the GPLv3.

Funding

This project was written while the author was receiving funding from the Irish Research Council's Government of Ireland Postgraduate Scholarship Program (GOIPG/2019/2798).