Fed Buffering Note Emlyn Corrin IC FED Meeting
Fed Buffering Note Emlyn Corrin, IC FED Meeting, 25 June 2003
Flow of Data in the FED
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 k. B per FED. • L 1 A Triggers at 100 k. Hz, Poisson distribution, Max rate of 140 k. Hz limited by APVE. • 200 MB/s / 100 k. Hz = 2 k. B = 5 strips / APV (4%) • 200 MB/s / 1. 5 k. B = 130 k. Hz
Zero Suppression, Front-End
Zero Suppression, Back-End
Raw Data Mode • Fixed event size: 280 10 -bit samples per fibre channel • A) 1 sample / 16 -bits : 52 k. B / FED 200 MB/s / 52 k. B = 3. 8 k. Hz • B) 3 samples / 32 -bits : 36 k. B / FED 200 MB/s / 36 k. B = 5. 5 k. Hz • C) 1 sample / 8 bits : 26 k. B / FED 200 MB/s / 52 k. B = 7. 6 k. Hz
Raw Data, Front End
Raw Data, Back End
VME Readout, Raw Data Mode Single FED Full Rack (17 FEDs) 10 MB/s 200 Hz 11 Hz 20 MB/s 400 Hz 800 Hz 23 Hz 47 Hz Assumes large enough buffer to absorb Poisson fluctuations in trigger rate.
Header Buffer
Header Buffer • Peak level of header buffer: proportional to size of data buffer proportional to trigger frequency inversely proportional to readout rate • For 2 MB data buffer, 100 k. Hz triggers, 200 MB/s readout rate, peak header buffer level ~ 12 000 events
Conclusions • Zero suppression mode, maximum occupancy at 100 k. Hz trigger rate = 4 %. • Raw data mode, maximum trigger rate: 3. 8 k. Hz, or 5. 5 k. Hz 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)
- Slides: 12