TPC trigger requirement meeting

Tuesday 7 May 2019, 10:00 → 12:00 Europe/Zurich

53/R-044 (CERN)

TPC PHYSICS TRIGGER mode requirements

TPC needs 2 commands sent from the CRU

• RESET : sent at the beginning of the run
• SYNC   : sent for a specific trigger.

Two main trigger scenarios have been discussed:

1. trigger is sent from the LTU to the CRU. This will open the readout window and send a SYNC to the TPC FEC. The SYNC trigger is sent immediately, the recording could be delayed with a programmable value (simple monostable, assuming no trigger pile-up)
2. trigger is sent from the TPC-FEC (pulser trigger) to CTP that will send the trigger to the CRU

CASE 1 is simple because the CRU will start collecting data after receiving the trigger from the LTU, so all the data generated by the FEC is collected. The CRU should have a configuration option to adjust the number of GBT packets (8kB) collected for every trigger (min 1 TPC drift time).

CASE 2 it is more tricky because when the TPC generates the trigger data has already left the FEE, there is a chance that the trip time of the trigger from FEC -> CTP -> CRU is too long and some data is lost while waiting for the trigger to arrive and open the readout channel. A different approach should be used.

To avoid to send SYNC message at every PHYSICS trigger, TPC proposed to use a counter that would count GBT WORD (GBT FRAME) so there is a reference in time to the first SYNC trigger received. Tests will be done to check if the BC and ORBIT (already present in each RDH) counter are ok as GBT FRAME counter (they are incremented every 25 ns).

We (CRU + CTP) should measure the trip time of the trigger signal, from the TPC FEC up to the CRU.

Other topics were discussed.

PREFETCH MEMORY in the PCIe BAR should be removed.

Possible issue in the ROC driver have been identified, TPC will contact the ROC developer for more details.

Issue in the SCA core concerning Transaction ID has been tested. The core can't be shared with multiple links, so a different solution should be studied.