Busy Box and related
Overview
Traditionally the Fee in ALICE sub-detectors indicates when its buffers are full and cannot handle further triggers from the CTP. This is either done directly or through the FANIN module to the LTU with a busy signal.
Due to dense cabling, four of ALICE sub-detectors (TPC, PHOS, FMD and EMCal), utilize a BusyBox to keep track of free buffers in their Fec. The BusyBox asserts the busy signal to the LTU when one of these conditions is true: Buffers in Fec are full, upon receiving a trigger sequence from TTC or when the TTC sends a global reset to the Fee. The BusyBox is located in the DAQ counting rom.