  TileCal is the central hadronic calorimeter of the ATLAS experiment at the
Large Hadron Collider (LHC). It is a sampling detector where scintillating
tiles are embedded in steel absorber plates. The tiles are grouped forming
cells, which are read-out on both sides by photomultiplier tubes (PMTs). The
PMT digital samples are transmitted to the Read-Out Drivers (ROD) located in
the back-end system for the events accepted by the Level 1 trigger system. The
ROD is the core element of the back-end electronics and it represents the
interface between the front-end electronics and the ATLAS overall Data
AcQuisition (DAQ) system. It is responsible for energy and time reconstruction,
trigger and data synchronization, busy handling, data integrity checking and
lossless data compression. The TileCal ROD is a standard 9U VME board equipped
with DSP based Processing Units mezzanine cards. A total of 32 ROD modules are
required to read-out the entire TileCal detector. Each ROD module has to
process the data from up to 360 PMTs in real time in less than 10 microseconds.
The commissioning of the RODs was completed in 2008 before the first LHC
collisions. Since then, several hardware and firmware updates have been
implemented to accommodate the RODs to the evolving ATLAS Trigger and DAQ
conditions adjusted to follow the LHC parameters. The initial ROD system, the
different updates implemented and the operational experience during the LHC Run
1 and Run 2 are presented.
