Possible changes to electronics

1. Possible changes to electronics Paul Dauncey Imperial College Some ideas on iterations to the design: • Reduce number of uplinks? • Remove large memory? Electronics changes

2. Reduce number of uplinks? Data rate on downlinks is minimal • Makes sense to use single (expensive) fibre to multiple FECs and split signals on DIC. • Saved £20k - £2k - £3k ~ £15k Less obvious to do the same for the uplinks • Data volume is high so reduces readout rate • Potential savings are ~ £18k (but might be more…) Electronics changes

3. Make uplink 16-1 also Complicates DIC; needs to combine 16 (one-bit @48 MHz) signals and feed into one fibre • Will FEC-to-FEC skew be small enough that no resynchronisation is necessary? • Will some intelligence be needed on the DIC, e.g. dual port RAM, to get data in phase again? Reduces data rate out of each FEC by factor of 16 • Look at when that dominates Electronics changes

4. Document design rates Data rates in current design • Large-to-small memory data reduction: ~20ms (independent of data contents) • Uplink readout: ~16ms per shower or 30ms for total large memory • VME readout (25 Mbytes/s): ~600ms per shower or 10s for total large memory Completely dominated by VME speed as uplinks run in parallel Electronics changes

5. Output vs input rates (1) Electronics changes

6. Reduced uplink rates Data rates with 16-1 uplinks • Large-to-small memory data reduction: ~20ms (independent of data contents) • Uplink readout: ~250ms per shower or 400ms for total large memory • VME readout (25 Mbytes/s): ~600ms per shower or 10s for total large memory Still dominated by VME speed but does have a non-negligible effect Electronics changes

7. Output vs input rates (2) Electronics changes

8. Implications for BEC (1) Would have only 6 fibre pairs from 6 DICs, so each BEC only has one fibre pair • Enough front panel space to combine all BECs into one board • Saving from PCB costs ~ £10k • Space for all components on one board? • FCT interface much simpler; single input • Could BEC become source of clock and StartTrain, i.e. effectively the FCT? Electronics changes

9. Implications for BEC (2) • With one board, is VME still sensible? • Direct interface to PCI card? (UCL?). May gain back some rate loss? • Still requires 250 Mbytes total of memory, with cost ~ £40k • Unless DICs now read one at a time, when only 40 Mbytes required, ~ £7k • Save substantial space on board • Implications for FEC synchronisation check; all FECs send handshake at same time Electronics changes

10. Reduced uplink rates Data rates with 16-1 uplinks + serial DIC readout • Large-to-small memory data reduction: ~20ms (independent of data contents) • Uplink readout: ~800ms (?) per shower or 2.5s for total large memory • VME readout (25 Mbytes/s): ~600ms per shower or 10s for total large memory Comparable with VME speed; halves original rate Electronics changes

11. Output vs input rates (3) Electronics changes

12. Remove large memory Large memory stores raw data before reduction; write reduced data directly to small memory? • Raw input data rate is 112 chs @ 12 MHz • Need to allow same output rate for peaks • Input is 10 bits/ch but output needs time stamp and gain/channel label so 30 bits/ch. • Use 200 pins/FPGA; (10 in + 30 out) x 5 ch; need 23 FPGA’s if no multiplexing. • E.g. output @ 24 MHz, reduce to ~14 FPGA’s Electronics changes

13. Other factors At low beam rates, speed dominated by large-to-small data reduction • Reduced from ~20ms to ~1ms, e.g. order of magnitude improvement for rates ~100 Hz. Cannot read out all raw data any more • Could only store ~10% directly Cost; large memory ~£400 saved on both FEC and BEC. 14 FPGA’s? Could be ~ £1000/FEC... • Probably not a saving overall Electronics changes

14. Summary • Combining uplinks at DIC would save ~ £18k, making a single BEC would save another ~ £10k and serially reading the FEC’s would save ~ another £35k, at a cost of a factor ~ 2 in speed at high rates • Sounds worth pursuing • Removing the large memories would possibly cost ~ £20k, reduce functionality but gain a factor ~ 10 in speed at low rates • Probably not a benefit overall Electronics changes