VEGAS Pulsar Project Meeting: 2016 February 1st 2:00 - 3:00pm ET

Room / Connection Details

• GB-137 / Soc 280
• 192.33.117.12##7144
• 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

Present

• Richard, Ryan, Scott, Marty, Justin, Paul

Agenda

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,
• c1500x4096 mode
  • Recompiled GPU transpose code
    • 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
    • Ryan to test at some point
  • Is this the SS version?
    • Previously no, but Ryan has starting testing this
• c1500x0512 mode
  • Build status
    • Built successfully
  • Scans failing during long integrations
    • Update status shared memory code to use different data type to accurately capture packet ID
      • Version built for Cuda 35, but need Cuda 75 for use on srbs (can't run these long scans using VEGAS hardware)
  • Astronomical verification
    • Used successfully during Breakthrough Listen tests (though with some packet loss in the RAW mode)
      • This loss was in the net thread
• 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
  
  • New filter coefficients
  • Spectrum output instead of time series
  • Implement PFB code
  • Could single GPU keep up with coherent dedispersion?
  • Reviewed John's email suggestion with Paul - more detailed query with John recommended
    • Is there an advantage to FFTs in FPGA? (none identified)
    • GPU (S/W) vs. FPGA (H/W)
      • GPU likely preferable if it can handle it
        • requires a benchmarking test
        • existing FPGA filter work could be affected
      • S/W CUDA-savvy resource constrained
        • Justin will look at it
    • How about running a higher bandwidth modes and ignoring some of the spectra?
      • limits on number of channels likely an issue
    • Ryan to email John to discuss some of this

Software

• Configtool changes
  • Ryan and Justin tested maintenace time
    • Overall everything went well. Both backends configured properly and successfully took data on the S-Band noise diode
    • Some remaining issues
      • VEGAS bandpass does not reflect the S-Band receiver response the way GUPPI does
        • 
        • 
        • Ryan, Randy, and Jason to test using noise source to try and isolate the problem (Tuesday at 1:00 pm)
          • TODO: What does it look like with just VEGAS?
        • All scans were with i0800x2048 mode
      • 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

• Status of new filters
  • Should be here in about 1 week

VEGAS/DIBAS-style backend for FAST

• Work progressing as independent project
• Any overlapping work to note at this time?

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 8