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

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

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

Frame numbering Use a Pseudo Random Bit Stream (PRBS) 001101111100011010110110000110101110110000010101001011 000110101 1 107 001101011 214 011010110 1 429 110101101 1 859 101011011 694

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.