Redesigning a Radio Frequency Control System with TACO
Why and How?
J. Meyer, J.L. Pons, J.L. Revol
European Synchrotron Radiation Facility (ESRF), BP 220
F-38043 Grenoble Cedex
FRANCEAbstract
During the construction phase the ESRF bought 3 radio
frequency transmitters as turnkey systems. Today they still
operate according to the original specifications, nevertheless,a decision was taken to redesign the control system of thesetransmitters.
The main reasons for this decision were maintenance andupgrade problems for electronics and software, the difficulties encountered with the technical evolution of the radio frequency transmitters and an insufficient integration into theaccelerator control system.
The goal of the new system was to build an easy to maintain and flexible control system, which can evolve technically, offer full user access to configuration and sequencing
and is integrated into TACO (the ESRF control system) andits tools.
This paper analyses the reasons which led to the decision
to redesign the radio frequency control system and the special needs we had to take into account in a research environment. Based on the new object oriented radio frequency control system, we will present our analysis, solutions and conclusions, from the hardware interface level up to the graphical user interface.

1 Introduction
Four radio frequency transmitters, with a maximum powerof 1.3 MW each, are presently installed at the ESRF. Threeon the storage ring and one on the booster.
In 1991 three radio frequency transmitters were bought asturnkey systems [10]. The hardware and software which wasbought still operates according to their specifications. The
control system still operates reliably and was designed as avery complex and powerful system for the 1991s.
Since August 1997 a fourth transmitter operates on the storage ring [2] with a new control system. The other three transmitters will be redesigned one by one without stopping theESRF operation.
2 Reasons for a new design
Several reasons led to the decision to redesign the old transmitter control system [1]:
 The company, where the transmitters have been bought,
does not exist any more.

Figure. 1. Scheme of a radio frequency transmitter To run the control system with a single 68020 CPU it

was optimised for speed. The result is a very complex
system with a high level of interconnectivity between
all tasks. Code changes are nearly impossible withouthigh risk for operation.
 To optimise the operation speed, no device drivers wereused. Direct memory access was implemented. Neither the low level electronics can be upgraded withoutmajor code modifications, nor can the OS-9 operating
system be upgraded, because memory access is protected in the actual releases.
 Technical improvements or more detailed diagnostics
cannot be integrated into such a closed and non modular system. Access on individual hardware parts orsequencing is not possible. At present new diagnostics
are build in parallel.
 The hardware protection is a part of the control system.

Figure. 2. Control system architecture and class structure
Hardware interlocks and software protection are tightlycoupled. Modifications on hardware protection are notpossible without detailed analysis of all software interactions in the control system.
 Configuration and diagnostics are only possible withlocal applications running under OS-9. The information is not available in the control room.
 A very poor integration to the surrounding ESRF control system and its tools. The different operation modesof the ESRF storage ring require more and more detailed equipment access for complex operations.
3 Design analysis
3.1 Why was the life cycle of the turnkey system so short?
After analysing the old transmitter control system design,
two major reasons were found for the short life cycle of 6years.
1. The radio frequency systems have been bought for aproduction process. The control system was not designed to evolve. Research institutes however need amuch higher degree of flexibility. The system must
evolve and improve all the time.
2. During the ESRF construction phase, the controls people were not closely enough involved in the radio frequency control system design.
 The software structure was not defined together withthe supplier. A working system was delivered, but
the software structure is much too complex to beflexible.

 When delivered, the implemented software structure

was not verified by the ESRF. Only the specified
functionality of the system was verified. Today weface a high level of interconnectivity where every
modification is a risk for operation.
 I/O electronics were not specified according to a setof maintainable I/O cards, used at ESRF. Only thereal-time operating system and the VME standardwere imposed.
3.2 How to guarantee a longer life cycle?
In order not to repeat the same mistakes we drew the following conclusions for the new control system design: Design the new control system object oriented. This
gives the best results for modularity and code reuse.
 Use in-house standards of hardware and software as
much as possible. TACO (the ESRF control system)[3][4] was used for all control aspects. This ensures acomplete integration into the existing ESRF accelerator control system.
Only standard ESRF I/O cards were used with their
TACO interface classes, a set of debugged and maintained classes for the ESRF accelerator and beamline
control systems.
 Do not outsource, but hire extra man power for thein-house development. This allows a much closer
control over design and development. Easy maintenance is possible if in-house people are involved in theproject. Technology transfer to an external company isnot necessary. Later changes and improvements can bevery efficient and cost effective.
 Separate hardware protection from the control system software. It must be possible to shutdown the control system without stopping the transmitter operation.
The hardware must be still protected by the independent interlock system.
 Implement regulation loops as software loops, if thetransmitter can operate for a short period of time
without software regulation. To improve the transmitter tuning a high degree of flexibility was requested.
 Give the system responsibles maximum access to thecontrol system. 90% of changes are requested for configuration changes, interlock changes, modified hardware interactions (sequences) and logging or trip diagnostic modifications. The turn around time for thesekind of interventions is shortest if the users are able tomodify the system themselves according to their needs.

the existing Tcl interface to TACO [6] (Figure 4). All
necessary TCL sequences to run the transmitter werewritten by the radio frequency group. Such Tcl scripts
are simple, interactive and very flexible for modifications.

4 Solutions
A general overview of the new control system structure isshown in Figure 2. The new radio frequency transmitter control system differs considerably in its implementation fromthe old system. Some of the more important differences are:
1. The hardware interlock system is based on a PLC
which was programmed by the radio frequency groupaccording to control’s specifications. A device server[1] reads from the PLC while graphical applications
are used to edit and visualise interlock logic diagrams.
The hardware responsibles are able to modify and diagnose all hardware interlocks without intervention fromcontrols people.
2. The object oriented design and the use of TACO allowed the reuse of all I/O interface classes, some general purpose classes (Figure 3) and a set of general purpose applications (example: archiver and fast data logger).

Figure. 3. Klystron tube device server class structure
3. To start and stop a radio frequency transmitter a lotof sequencing is necessary. A sequencer device server
was designed to run interpreted Tcl [5] scripts using

Figure. 4. Tcl script example
4. Synoptic applications only display information. All
intelligence was moved from the operation applications to high level object classes (Figure 5) and flexible TCL sequences. A graphical synoptic editor LOOX
Maker [7] was used, which allows to create pretty synoptics and modify them without touching the application’s code (Figure 6).

Figure. 5. Cavities devices access structure
5. Off-line diagnostics are implemented in three layers
to fit all needs. Data logging after transmitter trips
was installed with sampling rates of 200kHz and 10Hz.
Archiving can be configured with a maximum sam-2. The turn around time for modification requests was reduced. Most of the requests can be treated by the radio
frequency group.
3. Easy commissioning with a tight schedule for ESRF
operation. Responsibilities were shared with the radio frequency group for interlock installation, software
configuration, sequencing and configuration of diagnostics and archiving.
Big spin-off for other TACO based projects. General purpose classes and applications for tuning, monitoring and diagnostics, which were developed for this project, are reusedin different other projects for accelerator or beamline control.
The decision to use an open control system structure as a network of TACO objects, on all levels, offers high modularity.
Parts of the system can be improved or even replaced without interfering with other objects. In the near future external
objects could be integrated with the CORBA [9] standard.

Figure. 6. Klystron synoptic
pling rate of 0.1Hz for trend analysis.
All tuning, monitoring, archiving and trip diagnostics
are handled by a set of general purpose applications,which can be configured and adapted by the users to fit
their needs.

Acknowledgements
The authors would like to express their thanks toA.Beteva, I.Fladmark, P.Pinel and JM.Chaize from Computing Services and to the whole radio frequency group for their
help in design and implementation of the radio frequency
transmitter control system.

5 Conclusion
For a project of this size (Table I) in a research environment
in-house development is a good approach. The gain is highflexibility, easy in-house maintenance and low costs for further improvements.
With a simplified software development methodology (specdesign
design review
impleification document
testsdocumentation) and software stanmentation
dards (coding style, standard object interfaces and version
control) good results are possible without high overhead.
The close contact with the hardware responsibles and thepossibility to react on specification changes allowed modifications even in the development deadlines.
A similar conclusion was already drawn four years ago withthe redesign of the ESRF LINAC control system [8].

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Table I

Implementation statistics
Development time
Costs for VME crate and I/O cards
Classes written
Classes used
Applications written
Configuration resources installed

3.5 man years
˜37000 $US36486
˜3000

Giving the transmitter responsibles maximum access tothe control system has shown several advantages:
1. They do not see the system as a black box. By actively
changing the system behaviour, they understand the internal structure. Better diagnostics are done in case ofsystem failures.

References[1] “ESRF RF-Transmitter Automation System”, CapGemini SCS, CGSCS-Project No. C10024, March 1993
[2] “Construction of a Third RF Acceleration Unit for theESRF Storage Ring”, EPAC, Barcelona (Spain), 1996
[3] A.Götz, “TACO”,
http://www.esrf.fr/computing/cs/taco/taco.html,
ESRF, 1995
[4] A.Götz, W.D.Klotz, P.Mäkijärvi, J.Meyer, E.Taurel“TACO: An object oriented system for PC’s running Linux, Windows/NT, OS-9, LynxOS or VxWorks”,PCaPAC Conference, DESY, Hamburg (Germany), November 1996
[5] John K. Ousterhout, “Tcl and the Tk toolkit”, AddisonWesley Publishing Company, 1994
[6] G.Pepellin, “Tcl/Tk using TACO API”
http://www.esrf.fr/computing/cs/taco/tcltk/TclTk api.html,ESRF, 1996
[7] “LOOX Programmer‘s and User‘s Guide Version 3.2”,
LOOX Software, January 1996[8] J.M.Chaize, F.Barale, L.Claustre, P.Pinel “An ObjectOriented LINAC Control System”, ICALEPCS, Berlin(Germany), October 1993.
[9] “The Common Object Request Broker: Architectureand Specification, Revision 2.0”, OMG Document 9702-25[10] J.Jacob et al. “Commissioning and Operation of one
Booster abd two Storage Ring RF Acceleration Units atthe ESRF”, EPAC, Berlin (Germany), March 1992