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Fed Buffering Note

This document summarizes the key findings from the IC FED meeting held on June 25, 2003, focusing on the flow of data in the FED zero suppression mode. It presents critical metrics such as average event size, trigger rates, and the impact of different data handling modes on overall throughput. The report also examines the buffer requirements for handling Poisson fluctuations in trigger rates and discusses the implications of maximum occupancy and data rates for effective data management in high-energy physics experiments.

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Fed Buffering Note

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  1. Fed Buffering Note Emlyn Corrin, IC FED Meeting, 25 June 2003

  2. Flow of Data in the FED

  3. 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

  4. Zero Suppression, Front-End

  5. Zero Suppression, Back-End

  6. Raw Data Mode • Fixed event size:280 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

  7. Raw Data, Front End

  8. Raw Data, Back End

  9. VME Readout, Raw Data Mode Assumes large enough buffer to absorb Poisson fluctuations in trigger rate.

  10. Header Buffer

  11. Header Buffer • Peak level of header buffer:proportional 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

  12. Conclusions • Zero suppression mode, maximum occupancyat 100 kHz trigger rate = 4 %. • Raw data mode, maximum trigger rate:3.8 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)

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