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Realtime Aspects of PulsetoPulse Modulation
Riedel, Werner RSsch
Rudolf Steiner, Claus
5100 Darmstadt, Germany
GSI, Postfach 110552, D(
Abstract Graphic workstations are the operators' I/O tools
and software development platforms. The work
The pulsetopulse modulation of the SISESR stations are linked to a communication backbone.
control system is described. Fast response to Ethernet, Token Rings, or fiber optic links are
operator interaction and to changes in process candidates. The choice rather depends on the
conditions is emphasized as well as the essential distances to be mastered than on technical ad
part played by the timing system in pulsetopulse vantages or disadvantages.
modulation. To the same backbone, eventually as sub
networks with bridges in big systems, the equip
I INTRODUCTION ment control computers are connected, which are
mainly VME, Multibus, or CAMACbased.
The benefits of pulsetopulse modulation in accel Extensive use of graphics and CASE tools has
eration operating have been described as early as made an essential improvement in the operator's
'77 [1]. It is an effective way to increase the over and software designers' access to control systems.
all output of valuable beamtime of one or more The overall trend is from very special systems
accelerators. With beamsharing, rarely all users tailored to the very special task of accelerator con
of the beam will be unable to accept the beam at trol towards more uniform, general purpose sys
the same time. If the PPMhandling quickly re tems and the use of standards of the marketplace.
sponds to changing conditions, there will be virtu On the process level, however, the special needs
ally no deadtime in the machine operating due to of accelerator control, mainly realtime and syn
inevitable deadtimes of experiments, e.g. during chronisation, do still exist or are beconung even
new experimental setups. more complex. Therefore the functionality of a
In a multiaccelerator facility, PPM is almost control system must be biased by a timing sys
imperative. Asynchronously running machines, tem. The diversity of control systems of old has
every one of them operating as an injector for the it's evolutionary relic in the diversity of timing
next one, normally have time left between subse systems, which will resist standardisation trends
quent injections that can be used for experiments. for another while. The more the higher levels
in a control system become general purpose (and
II CONTROL AND TIMING SYS less realtime), the more processspecific problems
must be solved on the lower levels. This is the
TEMS domain of the timing system, the equipment con
trollers, and, of course, the equipment hardware.
Much has been said and will be said at this confer In the trend to general purpose systems the design
ence about the major trends in control systems in of the timing system determines the overall per
the last decade. Most systems recently designed formance significantly. The functionality of the
or upgraded are looking more and more similar: timing system may range from simply providing
345
clock signals for subsystem synchronisation to so III.1.2 Online Management
phisticated timing control of the equipment con
trol computers. However: A control system is only The operator may have a need to change either
complete with a timing system (Fig.l). the supercyde or the timing of an individual cycle.
The presently running cycle continues unchanged,
but the next one will have the modifications.
S3 & WORKSTATIONS
III. 1.3 Process Driven Management
COMMUNICATION
1 BACKBONE Process conditions may change and need fast re
EQUIPMENT sponse (suspend immediately one type of cycle of
CONTROL
COMPUTERS the supersycle) or even very fast response (emer
gency, dump the presently running cycle). Evi
dently this is beyond the operators' abilities and
TIMING must be handled on the process level.
SYSTEM For fast response, a request mechanism is very
useful: Cycles are only executed upon request.
Figure 1: A complete control system This is the appropriate level to feed in additional
conditions, as shown in Fig.2. Effective exploita
tion of beamtime is not the only aspect of PPM.
Security, radiation protection etc. are other ones:
A high energy beam must not be generated if it
PPMMANAGEMENT IN REAL cannot reach it's destination point properly.
III
TIME
Exparlaant an vanta baari?
III.l Realtime Demands of PPM ' SacuMty In «*r« *n7
' Hagnala in aara an ok?
vacuum in aara *n ok
vnat alaa nava you in *n..
The control system of Fig.l already contains all
realtime and synchronisation mechanisms to man Figure 2: Request Level
age the process, e.g. to execute a synchrotron
cycle. A system that can execute one cycle can Emergency handling is too special in every accel
as well execute another one. Nothing principially erator environment to be discussed here.
new needs to be introduced to perform PPM.
What then could be the realtime aspect of
PPM? Let me call it the 'online supeicycle man III.2 An Example: PPM Management
agement'. at SISESR
There are three levels of access to supercycle
management, with increasing realtime demands: Fig.3 shows the control and timing system of SIS
ESR. The timing system drives a timing network
in parallel to the communication network. Tim
III.1.1 Offline Management ing interfaces receive the serial timing information
and pass it as a 16bit parallel code, the event
The supercycle is built up offline to fit the exper code, to the equipment control computers.
imental program. The internal timing of the in A selectable set of events is transformed to
dividual cycles is programmed at the same time. hardware triggers for equipment by the timing in
There is no realtime demand. terfaces. The time jitter for triggers is smaller
346
than ±.5 microseconds in the system. Nanosec In comparison to other PPMsolulions, e.g. [3], no
ond timing has been left to special solutions to special PPMmanagement components like PPM
keep the timing system hardware simple. message decoders are needed at the process conrol
In contrast to Fig.l the timing system in Fig.3 level.
is not a special part in the control system. To the Fig.5 gives the operator's view of a simple super
operator it looks as, and in fact is, just another cycle.
equipment control computer.
D C D NC
? .5
WORKSTATIONS Count2 Count1 CountS
Active Active Inactive
R R NR
BACKBONE Figure 5: A SIS Supercycle
TIMING NETUORK
The properties assigned to each cycle are
EOUIPMENT I/O active/inactive
AND TRIGGERS execution count
decement/nondeciement
TIF: TIMING contiguous/noncontiguous
INTERFACES
all of which can be changed online by the opera
Figure 3: The SISESR Control Architecture tor. Active/inactive provides a simple means to
suspend a cycle. An inactive cycle does not leave
The SISESR timing system has direct timing a gap in the supercycle. It continues with the next
control over all equipment control computers [2]. active cycle.
Each equipment control computer has available The execution count works together with
complete settings to execute sixteen different cy (non)decrement and (non)contiguous.
cles, the 'virtual machines'. In nondecrement condition, (non)contiguous
The timing system activates machines by pro is meaningless. The subsequent supercycles are
viding the eventcode (Fig.4). The equipment identical containing as many individual cycles in
controllers do nothing unless they receive events, sequence as set by the count number.
command events, if nothing else, when no cycle With decrement and noncontiguous, the cycle
is active and the timing system is idle. In fact, will show up once in as many supercycles as set
the timing system of the SISESR is a hardware by the count, and suspended in the following su
dispatcher to compensate for the loss of realtime percycles.
abilities on higher control levels: It is the tim With decrement and contiguous, the cycle is ex
ing system that makes a 'real machine' out of a ecuted as many times as set by the count in only
'virtual machine'. This given, it is the natural one supercycle.
candidate to be the 'supercycle manager'. One type of cycle may show up at different
places in the supercycle, giving a high flexibility
for supercycle programming.
EVENT BUS Fig.6 gives an overview of the supercycles re
EOUIWCNT
is pit * my sulting from different settings provided the status
CONTROL
CO*»UTER from the request level is 'true'. If 'false', the cycle
CW»
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