Speaker
Description
Summary
A secondary function of the CMS Global Calorimeter Trigger system (GCT) is to provide
reordered HCAL Muon and Quiet bit data to the Global Trigger. This function is being
implemented utilizing a multi-gigabit switched serial mesh based processing topology.
It represents an evolution of the current GCT architecture, taking advantage of the
lessons learned implementing the optical data transmission and concentration between
the Regional Calorimeter Trigger racks and the GCT. This topology is realizable in
the micro TCA communications equipment standard, with a custom (though spec
compliant) backplane.
Traditional detector triggering systems have always been large hardware designs that
pushed the state of the art in both speed and density. Due to their optimization for
throughput, they have tended to be fully custom one-off systems, complex and
difficult to modify, and generally lacking in clean internal interfaces.
A more desirable architecture would support fine grained modularity, and be based on
a suitably flexible commercial standard, while supporting the extreme data rates
required of current trigger systems. Recent advancements in FPGA and data switching
technology, as well as the emergence of the Advanced Telecommunications Architecture,
have made it practical to consider a modular, commercial standards based architecture
for future triggering systems.
The GCT HCAL Muon and Quiet bit functionality entails the reorganization of the data
as collected by the 18 Regional Calorimeter Trigger crates, and transfer to the
Global Trigger (GT). In addition, the serial encoding of the data needs to be changed
to provide compatibility with the GT. While computationally fairly straightforward,
the number of channels (18, 1.6Gbit in, 24, 1.2Gbit out) is significant. This
communication intensive design is a good fit for an initial implementation of a micro
TCA based modular processing system.
The design is based on two main modules, a custom micro TCA backplane and a
processing module. The custom backplane is an intelligent micro TCA implementation
embedding hub functionality in the backplane. This allows the inclusion of large
crosspoint switches (Mindspeed M21161), creating a high performance data routing
fabric. A large FPGA (Xilinx V5LX110T) forms the basis of the processing modules,
which receive and reformat the data.
