Green Bank Ultimate Pulsar Processing instrument (GUPPI) Specifications

  • ALERT!= Probable
  • DONE= Will be provided
  • HELP= Not well understood, but we'll think about it
  • Editorial comments

General requirements:

  • DONE Publicly available from outset
  • DONE Architecture will be based on the CASPER FPGA technologies
  • DONE Independent machine i.e. does not use GBT spectrometer for ACFs
  • DONE Total system is not a substantial power or AC hog (this precludes us from doing everything in software with ~100 fast servers)
  • DONE High dynamic range sampling of baseband signal (at least 8-bit)
  • HELP Possibility for active RFI mitigation (at least for narrow band signals) Possibility there, but not understood well
  • DONE Dual polarizations in voltage; Full Stokes in power
  • DONE Both incoherent filterbank and coherent dedispersion capabilities


  • DONE "real" sampling baseband signals of BW from ~5 MHz to ~1000 MHz
  • DONE 8-bit digital samplers are part of the system
  • DONE timing information provided by 1 PPS and 5 or 10 MHz maser references
  • DONE expert-level user interface will get telescope and IF/LO information from GBT status database

Monitor and Control (prioritized)

  • DONE configtool support for telescope and IF/LO chain setup
  • DONE Viewing of firmware/hardware settings etc
  • DONE Ability to tap in to each section of system to have "scope"- like access to ADC, FFT, PFB performance
  • DONE Realtime passband and calibration monitoring


Output is sent to one or more data-handling machines

  • DONE Optimally, the data would be packetized over 10gigE
  • DONE The number of backend servers should be small (<~ 8, and optimally 1) in order to minimize power and AC requirements and improve reliability
  • DONE Data handling machines handle formatting (i.e. FITs), folding, downsampling, and writing of data to disk

Two types of basic output

  • DONE Phase 1: Incoherent filterbank (Polyphase or similar)
    • DONE 1 IF, 2 IF (unsummed or summed), or Full Stokes
    • DONE Should allow between 256-4096 channels (1K,2K,4K)
    • DONE Several BWs should be possible (~5MHz, ~20MHz, ~64MHz, ~200Mhz, ~600MHz, 1GHz+)
      • For Phase 1, optimally, the number of samples per second should be an integer (meaning that the channels or BW will not be an even number of MHz)
    • DONE Hardware output will optimally be "simple" (i.e. in order)
    • DONE Several quantization levels should be allowed 4-, 8-, 16-bit ints? (this could happen in hardware or by processing in the backend machines) Probably done in hardware
    • DONE Backend machines will write data in FITs format PSRFITS
  • ALERT! Phase 2: Coherently dedispersed subbands (processed in parallel)
    • ALERT! Total coherent dedispersion capability (to be handled in hardware) should cover at least 600 MHz (i.e. matched to clean chunk of S-band) for "high" DM MSPs (i.e. DMs <~ 300 pc cm-3). Optimally, BWs of up to ~1GHz would be great...
    • ALERT! Number of subbands should be tunable (up to 1K subbands)
    • ALERT! Subbands are folded in realtime or combined, downsampled and written to disk by backend machines
    • ALERT! Folding of multiple pulsars in hardware would be optimal, however, for many pulsars, we may need to use computer backends (Note: folding should likely use the new TEMPO2-style polycos) We can run the polycos in the Power PC on the FPGA

First priority demo machine specifications

  • 2 summed polarizations
  • Approx 600 MHz input BW (does not need to be an integer # of MHz)
  • 4096 channels
  • 50 microsecond integrations (exact 50us or not?)
  • 8 bits output word width (properly scaled during PFB stages to optimize dynamic range)
  • Total data rate is approx 83 MB/s sustained


  • Approved by Pulsar Project team members
    • DONE Paul Demorest
    • DONE John Ford
    • DONE Glen Langston
    • DONE Randy McCullough
    • DONE Scott Ransom
  • Approved by GBT Program Management
    • ALERT! Karen O'Neil
    • ALERT! Richard Prestage

-- JohnFord, ScottRansom, RandyMcCullough - 24 Aug 2007
Topic revision: r7 - 2008-02-05, PaulDemorest
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