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

Niko NEUFELD CERN, EP 2 The Event-builder

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

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

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

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

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

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

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

Niko NEUFELD CERN, EP 10 Backup Slides

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