dsa110-bbproc

Offline baseband processing of DSA-110 M8 voltage dumps — the raw int4 voltage fragments the dsa110-rt voltage_retention service stages on each corr node and C3 collects to h23 under /dataz/dsa110/candidates/<event>/Level2/voltages/.

The pre-M8 code (legacy T3-era beamformers, splicers, correlators) lives unchanged on the legacy branch.

Tools

toolkit

One binary, two modes (./toolkit -h for everything):

Coherent filterbank — the headline mode. Reads a candidate's 16 subband fragments, coherently beamforms the core antennas (82 of 96; outriggers excluded, same station≤102 definition as dsa110-rt) toward a candidate (l, m) offset from the meridian phase centre, and writes one full-band 6144-channel SIGPROC filterbank:

./toolkit -D /dataz/dsa110/candidates/EVT/Level2/voltages -E EVT \
          -P EVT.fil --l -0.0034 --m 0.0012 \
          -w beamformer_weights_XXX.dat --phase-only \
          --tscrunch 8 [--dm 168.8] [--rfi]

• Voltages are raw off the SNAPs — this tool applies calibration (-w, the same 74,496-byte beamformer_weights_*.dat blob the realtime system distributes), antenna exclusion (--core, -f, zero-gain cal entries), and optionally RFI flagging.
• (l, m) phasor convention matches the dsa110-rt injection system (dsart/inject/online.py): a source at (l, m) carries e^{+2πi ν (E·l + N·m)/c}; we beamform with the conjugate.
• --rfi enables Spectral-Kurtosis flagging with the same statistic and thresholds as the realtime flagger (dsart/rfi/sk.py, Nita & Gary 2010, MC thresholds at FAR 1e-4, per (ant, ch, pol, window)). Run with and without to compare. v1 implements the SK detector (dominant in practice); bandpass/group/sumthreshold are not ported.
• Memory: streamed block-by-block — a full 103 GiB event needs ~2.5 GB host RAM and ~600 MB GPU.
• Missing fragments are zero-filled (flagged on stdout).

Visibilities (legacy toolkit_dev parity, single fragment): correlate all 4656 baselines with optional time integration -t, per-baseline delay removal -d, 8× frequency averaging -a, and the baseline-sum filterbank -p/-g/-v. Output formats unchanged from the legacy toolkit.

fake_voltages

Synthesizes an M8-format event (fragments + manifests) containing thermal int4 noise plus a dispersed pulse at a chosen (l, m), DM, width, and amplitude — the C++/CUDA analogue of the dsa110-rt injection capability, for end-to-end testing without a telescope:

./fake_voltages -O /tmp/fake -E fake0000test --nblocks 4 \
    --l 0.002 --m -0.001 --dm 300 --width 16 --amp 1.2 -w cal.dat
./toolkit -D /tmp/fake -E fake0000test -P test.fil --l 0.002 --m -0.001 \
    -w cal.dat --dm 300

Build

On h23 (CUDA 11.1, RTX 2080 Ti):

make            # toolkit + fake_voltages
make test       # GPU round-trip: fake event -> filterbank -> S/N checks

Format ground truth

Pinned to dsa110-rt (see src/bbproc.h for chapter and verse):

• fragment = N × 288 MiB blocks, [2048 pkt, 96 ant, 384 ch, 2 t, 2 pol] int4-complex (real = low nibble), 32.768 µs native samples;
• band: channel 0 of sb00 = 1498.75 MHz (system channel 1024), descending by 250/8192 MHz across 6144 channels;
• cal blob: antpos_e[96], antpos_n[96], gains[96][48][2][2] float32, pol order [B, A], each coarse channel spans 8 fine channels.