Medium-Speed Feedback Software Based on the Existing Control System
A. Taketani, T. Fukui, K. Kobayashi, T. Masuda, T. Ohshima, R. Tanaka, T. Wada and A. Yamashita
SPring-8, Kamigori, Ako-gun, Hyogo 678-12, Japan
Abstract
The Equipment Manager(EM) model has been already
employed by the control system of the SPring-8 storage
ring. It is implemented on the client/server software
structure, and it accepts human-oriented commands fromclients on the operator consoles. The EM can access theVME I/O modules with reasonable execution time,
however, there is the application field to develop much
faster software on the CPU board by using the existing EMframework. A new software process - EM agent(EMA) isdeveloped as a virtual device which can be used for thefeedback purpose. This paper describes the development of
the EMA, and its performance is reported.
1 Introduction
The Equipment Manager(EM) is a RPC server process
which accepts the human-oriented command from a client
process and accesses the machine component through theVME modules[1]. It is general that a message has to besent from the operator console to the remote running cpu
over the network. It means that all message transactions
are suffering from the network overhead anytime. Itconcludes that there is a limit of the performance comingfrom the network overheard. The performance of the EM ismeasured to be 1msec typically for one device access. It
takes 0.8msec for resolving of the human-oriented
command to that of the corresponding hardware command,and 0.2msec for device driver calling. The execution time
between the MS and the EM is found to be 11msec for theround trip. It is indicating that most of the time is spent for
the network communication. It is good enough for most ofthe accelerator operation, however, there is the application
field to develop much faster software on the CPU board byusing the existing EM framework.
1.1 Equipment manager agent
The basic idea of the EM Agent(EMA) is to reduce thenetwork overhead. The EMA is developed as a virtual
device which can be controlled by the EM equivalently asthat of the real hardware device. One of the application
field of the EMA can be a software feedback system withthe medium speed, 10~20msec per one transaction. If wetry to make a feedback loop, the feedback process needs toread the equipment status, calculate the feedback values,
and manipulate the equipments according to the given
algorithm and parameters. The EMA is using the same
SVOC commands and calling the EM as the local call. The
similar sequence as of the GUI is implemented on theEMA. This allows the easy migration from the slower
control by GUI’s to the faster scheme with the EMA
procedures.

Figure 1. Schematic diagram of EMA.
2 Software structure
The EMA is developed with the same framework as thatof the EM’s. It is using the same function set and device
configuration tables. There are two parts in the EMA. Oneis the common frame part which manages the EMA
process control such as start/stop and the feedback
parameter setting (parameters are kept inside EMA as theinternal static values). The other is the feedback algorithm
part which accesses and manipulates the VME I/O
modules through the existing EM frame with the samedevice configuration file.
2.1 EMA frame
When the EM receives the create command, the EMA iscreated by the EM as the child process with the samedevice configuration file. The EM sends a start commandto the EMA, after starting the EMA process, the EM canmake communications by sending the command to andgetting the reply from the EMA through the message queuemechanism. The commands and replies are described inthe same message syntax as that of other EM commands.
The EMA is implemented as the virtual device which has
the feedback control by the parent EM.
The EMA frame checks the message queue at thebeginning of every feedback loop. If there is a commandfrom the EM on the queue, the EMA reads it and replies
immediately to the EM. The parameters for the EMA isdownloaded as the command strings without stopping thefeedback procedure. The EMA continues to run until it isstopped by the EM.
2.2 Algorithm
The algorithm implementation is very similar as that ofthe GUI. The sequence is made from a set of V/O/C andcoded into user functions. The data replied from the VME
I/O modules are stored into the local memory space andused for the feedback procedure.
3 EMA performance
For the EM, typically one I/O modules access takes
1msec for the resolving the human-oriented command. It isthe same for the EMA. The EMA needs another 1msec for
the frame part to handle the message queue. If one tries tomake 10 I/O accesses for reading and manipulating themachine components, it takes about 11msec in total insteadof about 100msec comparing to that of through thenetwork.
3.1 Application to the klystron control
We applied the EMA scheme for the klystron control as
the real case. The control process which ramps up theklystron power needs many feedback loops by reading
vacuum gauges and tuning the klystron power. During theramping up the klystron power, an arc may be caused in
the cavity due to the non-flatness of the surface. It happens
with the certain applied voltage into the cavity. The arc hits

the surface and kicks out the gases. Then the vacuum
pressures would be worse and the reflection power to theklystron is increased. Finally the klystron becomes to be
not operational.
The feedback loop reads the vacuum pressure gauges of
the RF cavities and controls the klystron power. The
response time of the vacuum gauge is about 20msec, it is
the slowest part of the feedback system. This feedback
procedure needs to monitor the 10 signals, that is, three forthe vacuum gauges, six for monitoring the klystron status
and one for the power controller. Additionally, thesemodules had been installed on the two different VME’s.
At the beginning we attempted this feedback loop with
the EM scheme by sending the control messages from RF
GUI to the EM’s over the network step by step. One loop
took 300msec including the GUI’s event loop. It was too
slow to catch up the changing the vacuum pressure.
We modified the hardware configuration such that all I/O
modules were hooked up to the single VMEbus in order tobe controlled by the same CPU. And the feedback system
was ported by using the EMA scheme. It provided good
performance, stable operation, and smooth ramp up of thepower.
This scheme has been newly introduced and working
since the beginning of the SPring-8 storage ringcommissioning.
4 Conclusion
We developed the EMA software feedback system. It has
been working as the part of the SPring-8 control system.
The applied field of the EMA can be not only the feedback
but also any fast looping procedures as the beam orbit
correction.
Reference[1] A.Taketani et al., Proc. of ICALEPCS’95, Chicago,USA, 1995, p.625.