The Central Trigger Processor Monitoring module (CTP_MON) in the ATLAS Level-1 Trigger System

The Central Trigger Processor (CTP) receives a 160-bit trigger pattern from the Calorimeter and Muon Trigger sub-systems at 40 MHz update rate, corresponding to the 25 ns bunch-crossing period of the LHC. This information is evaluated against a trigger menu to form the general Level-1 Accept (L1A) signal. The CTP Monitoring module (CTP_MON) monitors the trigger inputs of the CTP on a bunch-by-bunch basis in order to monitor trigger rates per bunch and detect any pathological bunches in the LHC machine. This information can also be used to estimate the luminosity per bunch. The monitoring system is able to build histograms of the input data at the maximum possible rate, with one 30-bit counter per input bit for each of the 3564 possible bunch positions in the LHC giving at least 26 hours of free running without overflow condition. The design and simulation of the CTP_MON will be presented.