1. Griffin Fostergriffin.foster@astro.ox.ac.uk Single Station Correlator(UNI)

2. Griffin Fostergriffin.foster@astro.ox.ac.uk A Widefield Imager Science:  Large field, short time resolution imaging for transient events.  Daily/Weekly sky survey Engineering:  Scalable FPGA based correlator design  GPU image processing backend  Prototype for large-N EoR arrays and SKA-Low Names:  SEPCAM (SEPnet CAMera)  LASI (LOFAR All Sky Imager)  UNI (UnNamed Imager)  …

3. Griffin Fostergriffin.foster@astro.ox.ac.uk Instrument Overview RSP x24 GPU Imaging Node FX Correlator LOFAR HBA Real Time Imager Post- Processing /Storage Server x192 FFT ANT 0 ANT 192 Cornerturn (192 Antennas x 1024 Channels) CH 0 CH 1023 CMAC

4. Griffin Fostergriffin.foster@astro.ox.ac.uk Correlator Specifications  FPGA Based (UniBoard)  96 dual-pol HBA antennas  → 18624 baselines  4 bit correlation  15-30 MHz Bandwidth  1024 FFT Channels  Integration times ~10 ms  Minimal modification to LOFAR station

5. Griffin Fostergriffin.foster@astro.ox.ac.uk UniBoard  Developed at ASTRON  8 × Altera Stratix IV 40nm FPGA, type EP4SGX230KF40C2, 1288 multipliers, 1517 pins  One front node → all back nodes mesh  14 layers  8 × 2 DDR3 modules  4 × 4 10GbE links in  4 × 4 8-bit LVDS out  Estimated maximum power consumption 280 W

6. Griffin Fostergriffin.foster@astro.ox.ac.uk Correlator Design Back Node FPGA 48 antpols/BN 4 BNs XAUI TX CLK @ 4 x Data CLK Low Band FFT EQ/4b Quant Cornerturn 48 antpol X Engine Xeng Out LVDS Mesh Front Node FPGA 256 Channels/FN 4 FNs CLK @ 4 x Data CLK LVDS Mesh FN1 FN2 FN3 BN1 BN2 BN3 Mux 192 antpol X Engines Vacc Xeng Out Daterates:  Input @ 25 MHz BW: 76.8 Gbps  Output: 141 MB per integration Processing:  6984 MACs @ 200 MHz: 1.4 TMACs  At 25 MHz BW complete correlation possible with 1 UniBoard UniBoard

7. Griffin Fostergriffin.foster@astro.ox.ac.uk RSP Interface AP 0 AP 1 AP 2 AP 3 BP RCU data RCU ctrl LCU Inter board interface (IBI) ring CEP serdes RCU data RCU ctrl RCU data RCU ctrl RCU data RCU ctrl Current RSP Design: Connected to adjacent RSP boards via a 4 lane(2.5 Gbps per lane) XAUI interface Utilizing:  Beamlets: 195312.5 Hz × 248 × 4 × 24b = 4.65 Gbps  Crosslets: 195312.5 Hz × 96 × 4 × 18b = 1.35 Gbps  Overhead: 0.025 Gbps  Total: 6.025 Gbps Modified RSP Firmware Design: Signal Channel correlator dropped, utilize 2 lanes for the beam ring and 2 for UNI. Requires a passive connector to split/combine XAUI CX-4 interface Utilizing:  Beamlets: 195312.5 Hz × 248 × 4 × 24b = 4.65 Gbps  Overhead: 0.025 Gbps  Total: 4.675 Gbps RSP Board CX-4 XAUI Connector

8. Griffin Fostergriffin.foster@astro.ox.ac.uk Firmware Design Options 12b Voltage samples 1  12.5 MHz BW/ XAUI Lane  Simplest firmware modification 8b Voltage samples (quant) 1  18.75 MHz BW/ XAUI Lane  Maximize BW/ XAUI lane, require EQ control interface 1 Limited band selection 18b Subband samples 2  8.5 MHz BW/ XAUI Lane  Simpler firmware modification 8b Subband samples (quant) 2  18.75 MHz BW/ XAUI Lane  Maximize BW/ XAUI lane, require EQ control interface 2 Selectable band, quantization required

9. Griffin Fostergriffin.foster@astro.ox.ac.uk Fast Transient Imaging  Channelized data is independent and is easily parallelized, GPUs offer a good solution  Short timescale images can be crude, thus traditional imaging steps can be simplified/ignored  But short timescale images must be formed faster then the integration time, the wide field of view also introduces a number of challenges. RFIcalib Array Model Sky Model Antenna Model phase φ 0 grid/w-projfft facet clean phase φ 1 phase φ n CompareThreshold Prev. Image 1 s Image 10 s image Storage GPU FX Detections grid/w-projfftclean grid/w-projfftclean

10. Griffin Fostergriffin.foster@astro.ox.ac.uk Widefield Sky Survey  Longer timescale transient events  New viewable sky survey every few days  Take advantage of the fast transient pipeline by using the post RFI, calibrated data  Perform secondary integration/data compression  Follow a more traditional imaging pipeline  Analysis will focus on rare, bright, transient events which occur on timescales of minutes to days

11. Griffin Fostergriffin.foster@astro.ox.ac.uk Where we are at Firmware:  Main modules (FIR,FFT,X Engine) currently being written  LOFAR RSP modifications and passive XAUI splitter done by ASTRON UniBoard:  First round of boards(7) have been produced and shipped to institutes Imaging:  Collaborators working on GPU imaging pipeline  Widefield imaging techniques in development on prototype array in Medicina Related:  AARTFAAC (Super Terp Correlator, ASTRON/U Amsterdam)