Trigger and timing distributions using the TTC-PON and GBT bridge connection in ALICE for the LHC Run 3 Upgrade

Abstract

The ALICE experiment at CERN is preparing for a major upgrade for the third phase of data taking run (Run 3), when the high luminosity phase of the Large Hadron Collider (LHC) starts. The increase in the beam luminosity will result in high interaction rate causing the data acquisition rate to exceed 3 TB/sec. In order to acquire data for all the events and to handle the increased data rate, a transition in the readout electronics architecture from the triggered to the trigger-less acquisition mode is required. In this new architecture, a dedicated electronics block called the Common Readout Unit (CRU) is defined to act as a nodal communication point for detector data aggregation and as a distribution point for timing, trigger and control (TTC) information. The ALICE trigger protocol in the upgraded triggerless readout architecture uses two asynchronous fast serial trigger links (FTLs) connections: the TTC-PON and the GBT. We have carried out a study to evaluate the quality of the embedded timing signals forwarded to the connected electronics using the TTC-PON and GBT bridge connection. We have used four performance metrics to characterize the communication bridge: (a) the latency added by the firmware logic, (b) the jitter cleaning effect of the PLL on the timing signal, (c) BER analysis for quantitative measurement of signal quality, and (d) the effect of optical transceivers parameter settings on the signal strength. Reliability study of the bridge connection in maintaining the phase consistency of timing signals is conducted by performing multiple iterations of power on/off cycle, firmware upgrade and reset assertion/de-assertion cycle (PFR cycle). The Intel® development kit having Arria® 10 FPGA is used for developing the prototype of the firmware. The test results are presented and discussed concerning the performance of the TTC-PON and GBT bridge communication chain and its compliance with the ALICE timing requirements.