Fed Buffering Note

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Fed Buffering Note
Emlyn Corrin, IC FED Meeting, 25 June 2003
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Flow of Data in the FED
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Zero Suppression Mode

• Average event size in inner layer of
  tracker,after zero-suppression 4 hit strips.
• Corresponds to 16 bytes per fibre channel,or
  1.5 kB per FED.
• L1A Triggers at 100 kHz, Poisson
  distribution,Max rate of 140 kHz limited by
  APVE.
• 200 MB/s / 100 kHz 2 kB 5 strips / APV (4)
• 200 MB/s / 1.5 kB 130 kHz

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Zero Suppression, Front-End
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Zero Suppression, Back-End
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Raw Data Mode

• Fixed event size280 10-bit samples per fibre
  channel
• A) 1 sample / 16-bits 52 kB / FED200 MB/s / 52
  kB 3.8 kHz
• B) 3 samples / 32-bits 36 kB / FED 200 MB/s /
  36 kB 5.5 kHz
• C) 1 sample / 8 bits 26 kB / FED 200 MB/s / 52
  kB 7.6 kHz

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Raw Data, Front End
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Raw Data, Back End
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VME Readout, Raw Data Mode
Single FED Full Rack(17 FEDs)
10 MB/s 200 Hz 11 Hz
20 MB/s 400 Hz 23 Hz
40 MB/s 800 Hz 47 Hz
Assumes large enough buffer to absorb Poisson
fluctuations in trigger rate.
10
Header Buffer
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Header Buffer

• Peak level of header bufferproportional to size
  of data bufferproportional to trigger
  frequencyinversely proportional to readout rate
• For 2 MB data buffer, 100 kHz triggers,200 MB/s
  readout rate,peak header buffer level 12 000
  events

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Conclusions

• Zero suppression mode, maximum occupancyat 100
  kHz trigger rate 4 .
• Raw data mode, maximum trigger rate3.8 kHz, or
  5.5 kHz if data packed.
• VME readout of raw data, 20 MB/s VME,400 Hz
  single FED, 23 Hz full crate.
• Header buffer could be made big enough to never
  overflow, but size required is large (12 000
  events)