VEGAS Pulsar Project Meeting: 2016 February 8th 2:00 - 3:00pm ET

Room / Connection Details

  • GB-137 / Soc 280
  • 434-817-6443

Housekeeping Details

  • Main wiki page
  • gbsapp Mailing List
  • Location and regular date and time of meeting - agreed weekly on Mondays; GB-137 / Soc-280; 2-3pm ET
  • ETK codes:
    • Electronics: 432510.GB3015
    • Software: 893252.GB3015
    • Science: 432540.GB3015

Resource Allocations

LYNCH, Ryan 0.15


  • Randy, Jason, Ray, Marty, Ryan, Justin, Richard


BOF file status updates

  • Switching signal builds
    • c1500x4096, i1500x2048, and i0800x2048 all seem to behave in the same manner as the non-SS builds
    • c0800x4096 mode scans fail to initialize
      • NETSTAT appears to remain in "Waiting" for too long, and Manager aborts because the hpc process is taking too long to start
      • This is because packets are not flowing
        • Ryan to double check addresses
        • Can also try it in DIBAS
  • c1500x4096 mode
    • Recompiled GPU transpose code
      • DONE Complete
    • nVidia profiling
      • BLI found using packet-sockets solves this problem and found them highly efficient. That code is done and available.
        • Will need to integrate this into current code, but other modes have higher priority
        • Ryan to contact Dave McMahon about these changes to see what needs to be done to incorporate them into our "release" (or pre-release versions)
    • guppi_daq_server version comparisons
      • No update
    • Is this the SS version?
      • This has been tested and performs identically to the previous build, i.e. scans run but with dropped packets.
  • c1500x0512 mode
    • Build status
      • Built successfully
    • Scans failing during long integrations
      • Ray built a guppi_daq version that uses the correct variable type in shared memory. This seems to have solved the problem, though the mechanism is still not entirely understood.
    • Astronomical verification
      • Used successfully during Breakthrough Listen tests (though with some packet loss in the RAW mode)
      • Ryan talked with Andrew Siemion about analysis of their pulsar data. This will be done in the near future.
  • c1500x2048 mode
    • Randy built a version with SS support
      • Ryan tested but there problems with bandpass
      • Low channels appeared to completely saturate, despite raw counts being within an acceptable dynamic range
      • Higher channels seemed OK
      • Randy and Jason are looking into the problem with this build
  • Fix for nchan calculation in coherent modes
    • verified - ready to roll into other modes
  • Bandpass issues in i0800x0064, 0128, 8192
    • Spent some time testing 64 channel mode
    • Injected a digital tone at 100 MHz, which always shows up at the correct frequency
    • Tone shows up in the correct bins, but generates spurs if injected at Fs/8 or nearby
      • Spurs move with the test tone and decrease with amplitude if you move away from Fs/8
      • May be problem with MMCM or OGP calibration
    • A suggestion was made to build a BOF with digital noise source to test
      • tough for 8192, others should be ok
        • test w/ 64 chl mode since testing already done by Jason
      • work needs to prioritized against other work
    • Jason worked with VEGAS hardware and saw same issues as on srbs
      • On srbs, spurrs were showing up when injecting a tone at Fs/4
    • DIBAS modes have clean bandpass
      • On VEGAS with AP, spectrum still looked poor, with spurs showing up
    • Result of discussions with Paul regarding OGP/MMCM calibration
    • Duplicated signal in i0800x8192
  • Low bandwidth modes
    • Need to decide on how to proceed with FFTs being done either on FPGA or by GPU. This is a hardware vs software approach.
    • If bandwidth is low enough all processing could be done on the GPU instead of the FPGA, but is there any advantage one way or the other?
      • More precision in the GPU
      • Could use one HPC to process full 200 MHz, otherwise need to do FFT on the FPGA
      • GPU code would have to do filterbank, not just coherent dedispersion
      • If done on the GPU, very minor changes to the BOF files, but need CUDA development (personnel is a problem)
      • If it is done on the FPGA, new BOFs have to be built, not clear how this would be done
      • In coherent dedispersion, time series would be fed into HPC, which would do a PFB/FFT, corner turn, FFT, complex multiply, FFT, accumulate
        • Need to add the PFB/FFT and corner turn, the rest is part of the coherent dedispersion algorithm
        • In incoherent mode, just do the PFB/FFT and then accumulate
        • Roach output would be the same as the spectral line modes, so we would have to merge the PFB/FFT, corner turn, and coherent dedispersion blocks, but these all exist
      • Another option is to use DSPSR, which can already do everything, but would use shared memory, which is going away


  • Configtool changes
    • Ryan did further tests to investigate bandpass discrepancies
      • VEGAS bandpass does not reflect the S-Band receiver response the way GUPPI does
        • GUPPI i0800x2048 S-Band.png
        • VPM i0800x2048 S-Band.png
        • VEGAS MODE3 S-Band.png
      • Issue seen when configuring only with VEGAS, and for older BOF file and newer SS-capable BOF file (both in i0800x2048 channel mode)
      • Spectral line mode 3 is similar to what we expect based on GUPPI
      • Same problem seen at L-Band
      • Injected tone recovered with GUPPI but frequency was wrong in VEGAS
        • Ryan and Justin tracked this down to an incorrect specification of IF3 in config tool and unexpected python behavior that could cause config tool to apply the LBW frequency shift in pulsar modes. These have been corrected but not tested.
    • Astrid reports that VEGAS fails to balance, although levels in the VEGAS power monitor seem normal
      • This is probably because Astrid cannot balance the requantization gain
        • This the equivalent of the guppi.scale / vegas.scale parameter. Can we balance this automatically in pulsar modes?
        • LBW gain so that dBFS is equivalent in and out of FPGA
          • There is an MR that describes balancing for spectral line modes
          • In spectral line mode this is handled during Balance
          • Are spectral line snap blocks in pulsar BOF files?
    • Astrid issued a warning about a discrepancy in the requested and actual IF rack power levels, though this did not cause a failure
    • An observer already expressed interest in configuring GUPPI and VPM in slightly different modes. We were not planning to support this but if we did, how much effort would it be?
      • Justin thinks this would be fairly easy
      • If we allow different scale parameters then we will have to support something like this anyway
      • Backend-specific parameters would probably be easy to set independently but higher level parameters like integration time would be harder to set independently
  • GBT Status shared memory parameters in PSRFITS headers
    • Done
  • Switching signal generation
    • Cal successfully controlled by VEGAS
    • Actual swper still not matching requested swper
      • Still outstanding
      • Justin to work on it some more this week
      • Incidentally, in dual backend mode DCR was automatically chosen as switching signal master
  • Matrix HPC
    • Justin has all threads running for all observing modes, and FITS files are being written
      • Need to check that FITS files are being written properly; Ryan to help with this
      • Richard suggests automating this by comparing FITS files with standards that are known to be correct
    • Justin working on VEGAS Manager to use Matrix instead of older guppi_daq
      • Justin hopes to have this done within 1--2 weeks.

GBT testing

  • Looking into VEGAS vs GUPPI bandpass differences

Wideband AP

  • Filters did not match drawings and do not fit circuit board
  • Need a new circuit board, then we have all the necessary parts

VEGAS/DIBAS-style backend for FAST

  • Work progressing as independent project
  • Any overlapping work to note at this time?
  • Proposed language concerning the effects of FAST on GBT pulsar observations. This is for inclusion in the FAST approval documents.
    • Effect on GBT pulsar science:
      • The overall effect of the FAST project on GBT pulsar observations should be completely mitigated by continued use of the GUPPI pulsar backend for current and planned timing observations. The beginning of parallel operation needed to verify timing solutions of VEGAS Pulsar and GUPPI match will be delayed up to three months if the VEGAS Pulsar work is completely terminated to free up the FAST project resources. If the shutdown is more targeted, it remains possible that the high-priority VEGAS Pulsar modes may be able to start close to the original schedule, but the medium and low priority modes will likely be delayed. This is not a problem as long as the GUPPI system continues to be reliable.
    • Approved?

Multicasting for spectral line and pulsar modes

  • Modifications to ROACH configuration and net task must bind to a multicast group instead of a specific host
    • All the 10-gig addresses on the ROACH would be multicast groups, and config will be told which to bind to
    • Some changes to net task code (in VEGAS HPC and guppi_daq code) to initialize sockets

Date / Time of Next Meeting

  • February 21

-- RyanLynch - 2016-02-08
Topic revision: r4 - 2016-02-08, RyanLynch
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