1. Status and Performance of the ALICE Trigger Electronics
David Evans
The University of Birmingham, UK
School of Physics and Astronomy, The University of Birmingham, Birmingham, UK
L. Barnby, M. Bombara, D. Evans, G.T. Jones, P.G. Jones, P. Jovanovic, A. Jusko,
R. Kour, M. Krivda, C. Lazzeroni, R. Lietava, Z. Matthews, S. Navin, A. Palaha,
P. Petrov, O. Villalobos-Baillie
The Institute of Experimental Physics of Slovak Academy of Sciences, Košice, Slovakia
I. Králik, L. Šándor
P.J. Šafárik University, Faculty of Science, Košice, Slovakia
J. Urbán

2. Layout of Talk Introduction
ALICE Physics
Running Conditions
Overview of the Central Trigger Processor (CTP)
Trigger classes
Sub-detector clusters
Past-future protection
The Local Trigger Unit
Emulation of the CTP
Error generation
Current status of the project

3. ALICE Physics Study of the strong interaction (QCD) at LHC energies
In particular, the quark-gluon plasma (QGP) and its properties
Collide Pb-Pb at LHC energies to form QGP
Also collide p-p as reference.
In addition, ALICE has extensive p-p physics programme.

4. Running Conditions
1 month per year – lead-lead collisions at 5.5 TeV per nucleon (1.2 PeV per Pb-Pb collision)
L ~ 1027 cm-2 s-1
Interaction rate ~ 8 kHz
Event size ~ 86 MB
7 months per year – proton-proton collisions at 7 TeV
L ~ 2x1033 cm-2 s-1
Interaction rate ~ 200 kHz
Event size ~ 2.5 MB

5. The ALICE Experiment Central Trigger Processor Size: 16 x 26 metres
Weight: 10,000 tonnes
Detectors: 18
Central Trigger Processor

6. Highlights of the ALICE CTP
Three levels of hierarchical hardware triggers:
L0 (1.2µs after beam interaction) → L1 (6.5µs) → L2 (88 µs)
At any time, 24 ALICE sub-detectors dynamically partitioned in up to 6 clusters.
Cluster configuration arbitrary and fully programmable – could be exclusive,
more likely to overlap.
Past-future Protection logic selects events with either no pile-up, or
a number of pile-up interactions up to a programmable limit.
Independent protection for each cluster; operates on all three trigger levels.
High data traffic over the TTC system
Channel A: L1 signal
Channel B: Orbit, Pre-pulse
But also, for each trigger:
L1 Data Message bit words
RoI Message - 4 words
L2a Message - 8 words
Upgrades:
L0 can be transmitted over TTC (as well as LVDS cable).
Status of trigger inputs now transmitted to DAQ at time of L0 trigger.

7. Position of TTC crate in ALICE
Racks are located below the Di-Muon magnet in cavern.
short latency for L0 – 1.2µs, but…
stray magnetic field
radiation
no access when beam is on
TTC crate supplies LHC clock direct to CTP and to Time-of-Flight detectors.
CTP sends L0, L1, L2 signals and messages to sub-detectors via individual TTC partitions.

8. Context diagram of the Central Trigger Processor (CTP)
CTP inputs
LHC timing – BC, Orbit
60 trigger inputs
24 L0
24 L1
12 L2
24 BUSY inputs
CTP outputs
24 independent sets
7 outputs per sub-detector
168 signals total
CTP readout
Trigger data for events accepted at L2 level
Interaction Record
CTP interface
ECS, DAQ, RoIP

9. Block diagram of the CTP
Synchronous, pipelined
processor
40.08 MHz bunch-crossing clock (BC)
Modularity and scalability
Logic blocks designed as
individual VME boards
6U form-factor
8 PCB layers
moderate density

10. CTP boards in a VME crate
Front panel connections
Timing inputs
Trigger inputs
BUSY inputs
CTP outputs
Interface links
Internal connections
Custom backplane

11. L0 Processor board - layout example -
VME interface
VME Controller FPGA
Flash memory
Trigger input LVDS receivers
L0 Logic FPGA
ADC, phase measurement
Snap-shot memory (1M x 32)
Backplane LVDS transceivers
ADC, supply monitor (I2C)

12. CTP board gallery L0 processor BUSY processor FAN-OUT board
In a VME crate …

13. Trigger (Physics) Classes
Trigger class - a basic processing structure throughout the CTP logic
There are 50 independently programmable “physics” classes
An additional test class - software-triggered, configured “on the fly” (application: calibration trigger, etc.)
“Rules of engagement”:
A cluster can be associated with an arbitrary number of trigger classes
A trigger class, on the other hand, affects only a single cluster
The associations are programmable

14. Generation of the Class L0 Trigger
Trigger input selection:
fully programmable
Shared resources:
2 Scaled-down BCs (1 – 109)
2 Random triggers (1 – 109)
4 BC Masks (1 bit per bunch)
Reduction of the class-trigger rate
trigger pre-scalers (1 – 106)
Cluster selection:
Cluster BUSY (1 out of 6)
Mandatory global vetoes:
DAQ BUSY (trigger enable)
CTP BUSY (CTP readout)
CTP Dead Time (1.5µs)*
All/Rare:
boosts the acquisition of
rare events
* Practically has no effect on trigger efficiency

15. Past-future Protection circuit
4 independently programmable circuits
at each trigger level (+1 for Test Class)
2 identical blocks, based on dual-port
memory
Sliding time-window during which the
interaction signal (INTa/b) is counted
Programmable parameters:
Protection interval (ΔTa/b)
2 Thresholds (THa1/2, THb1/2)
Output delay (a/b)
Output logic function
Delay and alignment of output signals

16. Local Trigger Unit (LTU)
Uniform interface between
the CTP and sub-detectors:
easier control
easier mods/upgrades
Unique features:
Full CTP emulation
(stand-alone mode)
Error emulation
(front-end tests)
VME, 6U form-factor
Similar to other CTP boards

17. Context diagram of the LTU
Front panel connections:
Inputs from CTP (LVDS)
Outputs to TTCvi, TTCex
L0, BUSY – sub-detector
TTCvi functionality now incorporated in upgraded LTU firmware (LTUvi)
Hence no longer used.

18. Block diagram of the LTU
LTU modes:
Global (run) mode - propagates CTP signals
Stand-alone mode - provides full CTP emulation

19. Switchboard CTP designed to handle up to 24 simultaneous L0 inputs
Recent hardware upgrade
CTP designed to handle up to 24 simultaneous L0 inputs
covered all known L0 inputs plus gave 6 spare at time of construction.
Explosion of possible L0 inputs in last 2 years 18  >40 (although not all needed in single run)
Solution: make Switchboard from programmable fan-in/out boards.
25 L0 inputs can be chosen from 50 at any time.
All 50 switchboard inputs can be monitored – even if not included in trigger.

20. CTP - September 2008
Beam pick-up T0
SPD V0
CTP in stable operation with up to 12 sub-detectors in single cluster and with multiple clusters. (i.e. several hours at a time of stable running).
During brief period of circulating beams:
Timing measurements for trigger inputs made and corrected in software.
Trigger on pixel detector (SPD) & trigger detectors.
Also triggers on bunch crossings
Trigger timing (before alignment) versus bunch number single shot
for SPD, V0, beam-pickup BPTX, T0 triggers

21. Summary
ALICE Trigger electronics installed and successfully commissioned with all major sub-detectors and control systems.
Several upgrades to hardware, firmware and software made since installation.
The ALICE trigger system provided stable operation during several months of cosmic ray running and during first beam from LHC in Sept 2008.
We are ready for looking forward to first collisions later this year.
Many thanks to the RT2009 organisers and thank you for listening.