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%\title{EUROGAM OVERVIEW}
%\author{M.M. Al\'eonard, P. Kadionik}
%\date{Edition 1.0\March 1991}
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EDOC122\par
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\small
Centre d'Etudes Nucl\'eaires de Bordeaux Gradignan\par
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\large
EUROGAM PROJECT\par
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\small
VxWorks in the Control System and Data Acquisition of the\par
EUROGAM Detector
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Edition 1.0\par
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March, 15th 1991\par
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\small
P. KADIONIK, M.M. ALEONARD\par
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%Centre d'~Etudes Nucl\'{e}aires de Bordeaux Gradignan\par
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CENBG-CNRS-IN2P3 France\par
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(33) 56.89.18.00\par
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\section{General overview :}
\subsection{Presentation :}
%\noindent
The EUROGAM multidetector array is built in a French-UK collaboration.
This is a system of 70 Ge diodes, each of these detectors is surrounded
by 10 BGO crystals. This array of detectors is used to detect gamma
radiations emitted in a nuclear reaction and measure their energy and
time correlation.\\
The general scheme of a data acquisition system in nuclear
physics is  shown in figure 1 :\\
 A high energetic beam of particles is sent on a target.
Radiations
issued from the nuclear reaction are collected by the detectors (EUROGAM
will detect gamma radiations). Pulses
ouput from detectors are then  shaped and digitized. General data
processing is applied before on-line analysis and storage...\\
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\subsection{System overview :}
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The electronic units necessary to process the analog signals ouput from
these detectors are  software programmable. Cards have been designed
in France in the new {\it VXI} standard (VME Extensions to Instrumentation).
Analog outputs from all these detectors are digitized in the VXI crates.\\
A fast {\it on-line} selection of these numeric data is realized by the
{\it Master Trigger} module in order to select the raw events. A
{\it raw event} is made up of all digitized data collected via
hardware units from
the various VXI crates after
trigger validation.\\
The raw events will be  formatted after data reduction by the {\it Event
Builder} processors (slow on-line filtering). The output data of this unit form
the {\it formatted events}.\\
An on-line control is supplied : the on-line histogramming  of data
counts versus their energy or time is built  {\it on-flight} from the raw events
in the {\it Histogrammer} crate with a hardware VME
Direct Memory Increment unit.\\
Formatted events issued from the Event Builder crate are saved in a list mode on
{\it Exabyte tapes} for {\it off-line} analysis (further delayed in time).
Some formatted events are sorted
on-line and their histograms are built in the {\it Sorter} crate.\\
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\section{EUROGAM architecture :}
The EUROGAM global architecture is shown in figure 2.\\
It is a  system distributed on an Ethernet network. All the CPU cards
connected
to E\-ther\-net are MVME 147 cards. These are the {\it Crate Controller} for eac
Crate (VME or VXI crate) connected to the network.
The Ethernet network is used to download tasks and insure the communications
between
the Crate Controllers and the whole architecture. \\
The {\it DT32} bus (32 bits bus in ECL logic) designed for EUROGAM project and t
{\it optical link} allow fast data transfers between crates.\\
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\subsection{VXI crates :}
Each VXI crate contains :\\
- a {\it Ressource Manager} card based on VXI standard (MVME 147 card coupled
with an interface to VXI designed in UK). This Ressource Manager is the
Master in the VXI crate and has also an Ethernet link.\\
- {\it Instrumentation } cards shape pulses issued from
the detectors and  digitize them.\\
- a {\it Readout Controller} card (ROCO) designed in France is in charge
of fast data transfer on DT32 bus (rate of 256k to 1M 32 bits words/s).\\


\noindent
The Master Trigger card is located in the first of these VXI crates.
It is responsible
for the general control and sequential readings of all data coming from the
Instrumentation cards towards each ROCO card (these form the raw event).\\
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\subsection{Histogrammer crate :}
The role of this VME crate consists in the on-line histogram building of
the current experiment. This histogram built in VME memory is used by
workstations
to check the experiment and control the detectors quality. The
histogramming unit is software programmable to select specific
parameters from choosen detectors and build their histogram via
a Direct Memory Increment in a global dual-port memory (VME/VSB).\\
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\subsection{Event Builder crate :}
The Event Builder basic functions is to format raw events and also filter them.
A  software selection is realized in order to filter raw events
according to physical expectations and reduce
the Event Builder output data rate. \\
The input data to the Event Builder are coming via a DT32/HSM interface (HSM
8170 from  CES). These data are processed by one of the MVME 165 CPU
cards working in parallel mode on different sets of data. The reformatted
events are then sent to a FIC 8232 card (CES) which
 transfers the formatted events through an   optical link to the
Sorter crate
(6 Mbytes/s rate).\\
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\subsection{Sorter crate :}
Among all the events coming in, only selected ones have special features
for the physicists towards their experiment. The {\it Sorter}
 unit is able to select
these specific events and enhance their features for control purposes.\\
The Sorter unit has a hardware architecture similar to the Event Builder unit
with MVME 165 CPU cards running in parallel mode in order to cope with
the data rate.\\
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\subsection{Storage crate :}
The {\it Storage} crate  saves all formatted events on Exabyte tapes.
Four Exabyte tapes will be used, each could work at a 512 kbytes/s rate.
Histograms built in
Sorter or Histogrammer crates may be saved  on these tapes too.\\
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\subsection{General monitoring procedure :}
Before starting the acquisition, all parameters must be set up : HV
detectors power
supplies, VXI instrumentation cards parameters... It represents
thousand of parameters values to set up. In this distributed
architecture, a general database reachable
through the Ethernet network is used to set the local databases.
The local databases are handled by the {\it Crate Server} software
located in the Crate Controller cards.
After the power-up phase, all the necessary set-up parameters values
are sent to the
Crate Server software.
Start or stop orders are sent in the same way to the Trigger or other
parts of the system (Event Builder,...).
The data acquisition control is managed from workstations which get on-line
collected histograms from the Histogrammer or Sorter units through the
Ethernet network. These histograms (or spectra) are transferred
 via a {\it Spectrum Server} software.
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\subsection{Visualization :}
Graphic workstations (SUN workstations) connected to the Ethernet network are
used to set-up, start, control and stop data acquisition and allow to
visualize the on-line histograms built in the Histogrammer and Sorter crates.\\
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\section{Software overview :}
\subsection{A distributed system :}
The software as the architecture has a distributed structure.
This system is based on
{\it Master/Slave} relationship.\\
Each crate is dedicated to a particular functionality in the acquisition line.
MVME 147 CPU cards are nodes in the Ethernet network.
These are the Crate Controller cards used as Crate Servers and
are gateways for the other CPU cards in the same crate.\\
Each Crate Server contains several software processes : a spectrum server, an
error
manager, a set-up software, control and diagnostic processes
in relation with the local database. A general
server software will route the procedures to the
appropriate
Crate Server(s) through the Ethernet network.\\
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\subsection{Choice of a Real Time kernel :}
This acquisition system must minimize the dead times
during the data acquisition. The
data flow is almost continuous and each detector "sees" on average
10000 events/s.\\
The data management is based on use of a {\it Real Time kernel}. This Real Time
kernel must be implemented in all CPU cards. It is to be performant and
complete, able to support efficient network communications.
It must be easily configurable
since several CPU cards are used in our system and they are from various
manufacturers. Besides, some of the  application tasks are to be often
reloaded depending on the evolution of the experiment. This must be done
easily by the physicist.\\
There are two aspects in Real Time applications in our project : an efficient
Real Time kernel is mandatory in the Event Builder and Sorter crates. For
control and set-up this aspect is less important but the communication
aspects take the lead.\\
The{\it VxWorks} Real Time kernel has been choosen for these criteria and
for its cross-development partnership with UNIX.\\
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\subsection{Communication procedures :}
The VxWorks environment  offers the UNIX environment facilities for
the programmation and
debugging.  Software are mainly written in C. However assembly language
68xxx may be used in specific cases for efficiency reasons, or
higher level languages like Fortran.\\
Communications are essential in this architecture. The
{\it Remote Procedure Calls}
 (RPC from SUN) are based on the {\it Client/Server} model. This is
the general communication mechanism between master and slave CPU cards.\\
A more general RPC library is written to be more suitable for specific
applications. \\
RPC will principaly ensure control operations and information
exchanges between the
different Crate Controller cards and the control workstations.\\
Communications in the same crate will be possible by the VME or VXI
{\it backplane} between the Crate Controller card (master) and the other
CPU cards (slaves). This is a very interesting feature from the VxWorks
kernel. However the efficiency of these communications are under evaluation
for in-crate communications in a Real Time context.\\
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\subsection{Set-up and control procedures :}
At power on each crate will be set in a given state : for example the VXI Crate
Servers will be able to give a status and mapping of all the Instrumentation
cards in their crate. In a second step, the set-up phase, these informations
will be compared to the expected ones from initialization routines governed
by the physicists. The set-up processes are to load all the necessary parameters
(about 1500) in all the Instrumentation cards. The procedures are not time
critical.\\
Once the set-up phase is performed, the acquisition start-up is possible. At thi
point the sequential ordering in time of execution of the start-up
procedures is crucial for the goodness of the data collected : one task will
be in charge of this start-up.
When the acquisition is turned on, the Real Time performances of the software
are requested in all processes  dealing with the events coming out from
the Instrumentation cards. The rate of events that could be handled by
the Event Builder processors could be as big as 1M 32 bits words/s in the
upgraded version of EUROGAM.\\
In parallel to this events management, storage controls are to be implemented
to check the quality of the experiment. Amoung the procedures, counting rate
checks of the detectors insure that all the detectors and electronic performs
well. These checkings can be done through the integration or analysis of
histograms built on-line and on-flight.
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\subsection{Event Builder software :}
The Event Builder software collects the raw events from several crates and
builds a new formatted event with eventually new parameters for
further storage. This filtering processes of the data provided by the
High Speed Memory (HSM 8170 card) will be duplicated in several MVME 165
CPU cards. These filterings will be controlled by one arbitration
task which will also direct the filtered events towards the optical
link transfer process.\\
The arbitration unit needs also have control of the data rate managed by
the various CPU cards and error management.\\
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\subsection{Sorter software :}
The organisation of these functions is equivalent in structure as
the Event Builder one with arbitration task and parallel processes dealing
with sequential data records.\\
The sorter software is a further filtering of events to build histograms in
one or two dimensions. Parameters for this filtering are often changed.
These changes need reloading procedures easily implemented.\\
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\subsection{Test procedures :}
A general tests software has been written to allow several  basic
tests of memories and
registers on all developped cards. It is a simple user interface between
the board designer and the VxWorks environment.\\
Specific procedures are developped for testing the data path consistency too.\\
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\section{Conclusion :}
The first phase of the EUROGAM project will be in operation for the end of
summer 1991 in Daresbury (UK). The multidetector will have just 45 Ge and
450 BGO detectors.\\
The upgraded phase is expected for the end of summer 1992 in Strasbourg (France)
with a final configuration of 70 Ge and 700 BGO detectors.\\
EUROGAM hardware and software structure will also be implemented on other
multidetector arrays in design in France : DEMON, ICARE...\\


\noindent
The software development for EUROGAM result from a collaboration of
ingeniors working in several laboratories supported by IN2P3 in
France and SERC in UK. These la\-bo\-ra\-to\-ries are CENBG (Bordeaux),
CRN (Strasbourg), IPN (Orsay), CSNSM (Orsay) in France and
Daresbury Laboratory, Oliver Lodge Laboratory in UK.


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