1. Thoughts over a data acquisition system for reading out KM3NeT Optical Modules

2. Data Communication Real-Time Semi Real-Time Store and forward
Need High Bandwidth
10 Gbps => 100 ps/bit => 10 PMTs in a 1 ns slot
More than 10 PMTs => determine priority and accept that you sometimes loose data
Link utilization not 100%
Data
Some framing overhead
Some link
synchronization overhead
delay
Semi Real-Time
Postpone a transmission and code the delay in the data
Data can be smeared over time => lower bandwidth => less power
Need some electronics (FPGA)
Store and forward
The same electronics could timestamp events
Timing transfer over data-link phase-locks and calibrates the Local Clock
Low bandwidth
On shore data is already pre-formatted

3. Frame Numbering and Calibration
Data
N+9
N+11
N+10 1
N+8
N+10
N+9
N+11 1
N+5
N+7
N+6
N+8
N+9 1
N+11
N+10
Data
Data
N+10 1
N+11
N+7
N+9
N+8
N+10
N+11 1 1
Data 1 1
Data 1
Data
N+4
N+6
N+5
N+7
N+8
N+11
N+10
N+9 1
Data
Data
N+11 1
N+6
N+8
N+7
N+9
N+10 1
N+11
Data
N+4 N
N+2
N+1
N+3
N+7
N+6
N+5
N+8
N+3
N+5
N+4
N+6
N+7
N+10
N+9
N+8
N+11
Data
N+1
N+3
N+2
Data
N+4
N+5
N+8
N+7
N+6
N+9
N+2
N+4
N+3
N+5
N+6
N+9
N+8
N+7
N+10
Data N
N+1
N+1 N
N+2
N+1 N
N+2
N+6
N+5
N+4
N+7
N+3
N+1
N+2
N+5
N+4
N+3
N+6 N N
N+1
N+4
N+3
N+2
N+5
N+2
N+1 N
N+3 N
N+3
N+2
N+1
N+4 N
Optical
Module
Reference
Clock
Propagation Delay
Is known!
(8 Frames in this example)
Shore
Station

4. Frame numbering Use a Pseudo Random Bit Stream (PRBS) 1
107
214 1
429 1
859
694

5. Conclusion
All Receivers (in Optical Modules and in Shore Station) are phase locked to the Shore Station Transmitter Clock.
Calibration is done automatically and constantly. Data can be corrected on the fly.
Frames can be numbered with a 1-bit overhead.
This proposal fits both “Semi Real-Time” and “Store and Forward” concepts.