Green Bank Ultimate Pulsar Processing instrument (GUPPI) Specifications

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

General requirements:

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

Input

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

Monitor and Control (prioritized)

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

Output

Output is sent to one or more data-handling machines

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

Two types of basic output

• Phase 1: Incoherent filterbank (Polyphase or similar)
  • 1 IF, 2 IF (unsummed or summed), or Full Stokes
  • Should allow between 256-4096 channels (1K,2K,4K)
  • 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)
  • Hardware output will optimally be "simple" (i.e. in order)
  • 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
  • Backend machines will write data in FITs format PSRFITS
• Phase 2: Coherently dedispersed subbands (processed in parallel)
  • 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...
  • Number of subbands should be tunable (up to 1K subbands)
  • Subbands are folded in realtime or combined, downsampled and written to disk by backend machines
  • 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

Approval

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