1. 1 Event Building L1&HLT Implementation Review Niko Neufeld, CERN-EP Tuesday, April 29 th

2. Niko NEUFELD CERN, EP 2 The Event-builder

3. Niko NEUFELD CERN, EP 3 Event-building All Readout Units (RUs) send frames to the same destination based on the event number The destination is a NP module, which – waits for all frames belonging to one event –concatenates them in the right order –strips off all unnecessary headers –sends the completely assembled events to the SFCs –handles a small amount of reverse direction traffic

4. Niko NEUFELD CERN, EP 4 Architecture NP Event Builder Readout Network Switch NP SFC Storage Controller Sorter TFC System

5. Niko NEUFELD CERN, EP 5 Optimising the link-load The input date rate into an event builder module is chosen to be ~ 110 MB/s The output is ~ 75 MB/s (due to the reduced overheads) Since it is advantageous to minimise the number of subfarms (and hence SFCs, c.f. next presentation) a suitable multiplexing using switches is done to bring the link-load into an SFC again up to 110 MB/s, i.e. in the above case 3 event builders feed into 2 sub-farms

6. Niko NEUFELD CERN, EP 6 Some numbers for the Velo/TT (=baseline) scenario Output Links from Readout Network72 Mean output from Readout Network per link108.7 MB/s Fragment Rate (L1) per link585.6 kHz Fragment Rate (HLT) per link8.9 kHz Event Rate (L1) per Link15.3 kHz Event Rate (HLT) per Link0.556 kHz Mean output from event-builder for L156.5 MB/s Mean output from event-builder for HLT18.8 MB/s Aggregated output from event-builder into sub-farms75.4 MB/s Number of event-builder NPs36

7. Niko NEUFELD CERN, EP 7 Event-building in the NP Fragment rate is very low compared to the multiplexing after the front-end: 500 kHz for L1 Technically fragments are concatenated in the output stage of the NP (large output buffer of 256 MB) From studies of frame-merging it is known that merging rates of well over 800 kHz can be easily achieved Only technical complication: resulting events can be larger than allowed Ethernet MTU  segmentation must be performed

8. Niko NEUFELD CERN, EP 8 Event-Building vs FE muxing Fragments of same colour have same event-number Necessary information for merging contained in the header Transport errors (timeouts, CRC errors) are recorded in a trailer

9. Niko NEUFELD CERN, EP 9 Data-format (HLT)

10. Niko NEUFELD CERN, EP 10 Backup Slides

11. Niko NEUFELD CERN, EP 11 Data flow in the NP4GS3 Ingress Event BuildingEgress Event Building DASL Access to frame data