Green Bank Ultimate Pulsar Processing instrument (GUPPI) Specifications
Legend
= 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)