This program is part of the data handling pipeline for the AA-ALERT project. See dadatrigger for an introduction and dataflow schema.
$ mkdir build && cd build $ cmake .. -DCMAKE_BUILD_TYPE=release $ make $ make install
$ dadafilterbank -k <hexadecimal key> -l <logfile> -n <filename prefix for dumps>
Command line arguments:
- -k Set the (hexadecimal) key to connect to the ringbuffer.
- -l Absolute path to a logfile (to be overwritten)
- -n Prefix for the fitlerbank output files
Modes of operation
The program implements different modes:
- mode 0: Stokes I + TAB (12 tied array beams)
- mode 2: Stokes I + IAB (coherent beams, so only one tied array beam)
Not supported modes:
- mode 1: Stokes IQUV + TAB
- mode 3: Stokes IQUV + IAB
The data rate is set per science case. Supported cases:
- case 3: 12500 samples per second
- case 4: 25000 samples per second
Metadata is read from the PSRdada header block. Note that some of the metadata available in the header block is ignored, due to code constraints and optimizations. For values that should be present see the table below.
|MIN_FREQUENCY||Center of lowest frequency band||MHz|
|BW||Total bandwidth of the observation||MHz|
|PADDED_SIZE||Length of the fastest dimension of the data array|
|SCIENCE_CASE||Mode of operation of ARTS, determines data rate|
|SCIENCE_MODE||Mode of operation of ARTS, determines data layout|
A ringbuffer page is interpreted as an array of Stokes I: [NTABS, NCHANNELS, padded_size] Array padding along the fastest dimension is implemented to facilitate memory copies.
Filterbank output files
Tied array beams are written to separate files, one per observation. Note that these files can become very big.
Filterbank file names are derived from the file name prefix (-n option).
- For science mode 0, .fil is appended, resulting in prefix.fil
- For science mode 2, both tied array beam number and .fil is appended, resulting in prefix_NN.fil.
To prevent issues with relative paths etc., please use fully resolved absolute paths (starting with a '/').
To connect to the PSRDada ring buffer, we depend on some object files that can be obtained when compiling PSRDada. The location of these files is assumed to be in the PSRDADA directory. Alternatively, set SOURCE_ROOT such that the files are in SOURCE_ROOT/src/psrdada.
Building is then done using the Makefile:
Altough the program is relatively simple, the large arrays can cause performance issues wrt. caching. The matrix transpose and inversion of the channel dimension takes longer than realtime using a naive implementation on the ARTS cluster.
In the tune subdirectory there are several implementations trying out different loop order and various levels of loop unrolling. It also adds openMP, with the number of threads specified in the Makefile. As a final step, you should pin the executable to a specific core using taskset.
To try them run:
cd tune make all make time
For science 4 on the ARTS cluster, the loopct_r6 implementation was fastest (using 2 to 4 threads); this is current implementation.
Jisk Attema, Netherlands eScience Center Leon Oostrum, UvA
- maximum length of source_name is currently 255 characters. Longer names will result in undefined behaviour in dada functions.
- The number of frequency channels is hardcoded to 1536, the number of bits to 8.