Lucas, P W

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Particle Accelerators, 1990, Vol. 29, pp. 191-196Reprints available directly from the publisherPhotocopying permitted by license only© 1990 Gordon and Breach, Science Publishers, Inc.Printed in the United States of AmericaTHE TEVATRON CONTROL SYSTEM - 1989PETER W. LUCASFermilab*, Batavia, IL, U.S.A.Abstract The Tevatron control system, which runs all of theaccelerators and storage rings at Fermilab, is being upgraded ina number of areas. These include: networking, front endcomputers, console computers, and microprocessor environment.Details of each of these upgrades are presented.INTRODUCTIONThe system known sometimes as ACNET and sometimes as Tevatron controlsis a comprehensive one used to operate all the accelerators, storagerings, and the fixed target switchyard at Fermilab. Although therehave been changes in detail, particularly expansions, there have beenno upgrades or chang~s in concept since the specification of thissystem around 1980. However since that time there have been majoradvances in the computer field, particularly involving networking,graphics and the user interface, and microprocessor utilization tools.Thus four major modernizations of ACNET are taking place to make useof these advancements. A fifth upgrade is to bring the Main Ringcontrols, which predate the Tevatron by several years, up to the levelof those of the other accelerators; however this work involves no newtechnology and will not be discussed further here.This paper details the motivations of the various upgrades,indicates for each the path chosen, and provides a status report. Itshould be noted that all the work described must be performed in thecontext of a running accelerator complex; no shutdowns have resultedor will result from any of the modifications described.A schematic diagram of the system nodes, as they exist atpresent, is given in Figure 1.*Operated by Universities Research Association under contract with theU.S. Department of Energy[893]1191192/[894]HOSTMICRO-PROCESSORSFIGURE 1NETWORKSP. W. LUCASTEVATRON CONTROL SYSTEM COMPUTERSACNET node diagramOB-01-nThe choice for a new Local Area Network (LAN), as well as Wide AreaNetwork (WAN), is IEEE 802.5 Token Ring as implemented on the chip setproduced by Texas Instruments, Inc. In the LAN case this networkreplaces the proprietary Digital Equipment Ccorporation PCL product.The motivation for the change is the lack of ability to connect PCL tomodern DEC equipment - such as the MicroVAX line of computers - or anyequipment from other manufacturers. In the WAN case the Token Ringaugments, but does not replace, serial Camac.Hardware has been constructed by us for interfacing Unibus (VAXand PDP-11) and Q-bus (primarily MicroVAX) computers to Token Ring,and software drivers for the RSI and VMS (as well as ELN, though notused in ACNET) operating systems have been written. Additionallyinterface hardware for VME based equipment has been purchased and thatfor Multibus II is under construction. The status is that the LAN isnow totally converted, with some remnants of PeL remaining in thesoftware (in particular packeting of messages as required by PeL); theWAN ring hardware is also functional, but its connection to the LANremains to be made.Most users of DEC equipment, such as ourselves, choose Ethernetfor networking due to easy compatibility with their computers andTHE TEVATRON CONTROL SYSTEM [895]/193strong support from the company. As is indicated in Figure 1, weindeed do have Ethernet connections on our host VAX computers, andthis is utilized for external communications. However we have optednot to use that protocol for real time control system communications.The reason for this is that the means of sharing the hardware mediumin Ethernet, a collision detection scheme, does not work so well in asynchronous environment, such as that of an accelerator, as does thetoken passing scheme of 802.5.FRONT END COMPUTERSFront end computers in ACNET are used as drivers of hardware links,specifically Camac for the modern accelerators, PDC for some of theolder equipment, and Ethernet for the Linac. The particular concern iswith the Camac drivers which reside at the heart of the system -translating between the hardware engineer's view of the acceleratorand the more abstract one of programmers, operators, and physicists.At present the front ends are all PDP-11 computers, coded inassembly language. They are system bottlenecks both in terms of datathroughput, being able to utilize only about 10~ of the Camacbandwidth, and in terms of personnel, since a limited number ofindividuals are able to work on such machines.A survey of commercially available computers which might serve asfront ends yielded nothing with the appropriate speed and real timecharacteristics and at an affordable price. The answer as to the bestway to turn, as it often is in the computing field at this point intime, was to institute parallel processing among a number ofrelatively inexpensive microprocessors. Thus each front end consistsof one to several (perhaps three) single board computers utilizing theIntel 80386 processor and housed in a Multibus II chassis. The 80386was chosen based on performance, price, availability, and the factthat its memory storage byte order for 16-bit words is the same asthat of a PDP-11; this latter condition ruled out the Motorola 68OxOprocessor line. Multibus II was chosen (over VMEbus, the only viablealternative) as a modern backplane with many features conducive toefficient engineering development; it is also a natural home for the80386, coming from the same manufacturer.194/[896] P. W. LUCASInsofar as possible the code for the new front ends is beingwritten in C, tnough at very low levels some assembly language isstill required, The MTOS operating system kernel, VAX baseddevelopment tools, and convenient debugging environment are availablefor this work as for other microprocessor projects as discussed indetail below.The status is that a prototype system has been purchased and thatabout half the software and Fermilab built hardware are completed.VAXSTATION CONSOLESModern engineering workstations provide a powerful and cost effectivemeans of producing new accelerator operators' consoles. Some suchdevice is required at Fermilab due to the obsolescence of much of thedisplay equipment of the existing consoles, the need for moreconsoles, and the desire not to purchase more outdated equipment. Ourground rules are that all programs operating on the present PDP-IIconsoles shall also operate on the new ones with minimal alterations,and that the new ones shall be able to co-exist on a network with theold. The first condition is required so that the extensive softwareeffort expended in producing console application code not be wasted orduplicated as the new devices evolve. The second condition is based onthe fact that the twenty old consoles represent a considerableinvestment in hardware, and should be kept in operation even as newones are produced. This latter condition, due to the byte-orderproblem also confronted in the selection of new front ends, rules outmost Unix workstations and has effectively limited the decision to achoice between VAXstations from DEC running the DECwindowsimplementation of the X-windows user interface, and PS/2's from IBMrunning the Presentation Manager interface. VAXstations have beenselected due to more advanced software.As compared with the PDP-II based consoles the VAXstation basedones have better performance by a factor of roughly five forcomputation and eliminate the problem of minimal addressable memorywhich haunts all PDP-11 work. In particular commercial softwarepackages which will not fit on a PDP-II can be installed on aMicroVAX, and a totally unproductive software activity of overlayingprograms in such a manner as to fit in a limited memory is eliminated.THE TEVATRON CONTROL SYSTEM [897]/195A benefit of the greater processor speed and memory, as well as of themodern windowing environment, is that a greater number of programs canbe run simultaneously than was previously possible, and that terminalemulation and debugging can be done on the same screen used for actualconsole displays, much aiding the software development process.Despite all these advantages, the cost of a new console is less thanhalf that of an old one, and can be expected to decrease with time.The status of this project is that, with only a few exceptions,all of the software of the old consoles has been ported to the newones and minimally tested. The new consoles are temporarily networkedvia Ethernet rather than Token Ring, and real time clock signals arenot yet available in them. Though these consoles could in principle beused to run accelerators now, the software - primarily X-windowsitself - is not yet sufficiently robust.Two major decisions remain to be made, involving the number ofscreens attached to a given console and the evolution of software inthe new environment. An old console contains five display devices,which are emulated by windows in a new one. Putting this muchinformation on one screen, and more information if several programsare running simultaneously, leads to a cluttered appearance andinability to view at one time all the necessary data. Thus more thanone screen must be made available, at least for any console actuallyused to run accelerators. Choices as to how to accomplish this involveeither multi-screen VAXstations or X-server terminals, which are nowbecoming available. As to software evolution, all programs thus farhave been, as mentioned, ports of ones from the PDP-11 environment andthus have not taken full advantage of the power of the new stations.Software will evolve in interesting new ways as developments specificfor the new consoles are undertaken.MICROPROCESSOR ENVIRONMENTIn the past all microprocessors in the system communicated to consoleand other computers over a hybrid link of which Camac formed a majorpart. Communications for new systems will involve the much moresophisticated Token Ring. The added flexibility of this new medium, inparticular allowing subsystems to generate and send messages without196/[898] P. W. LUCASany outside request to do so, has led to a new protocol known as OOC(Object Oriented Communications) which is under development.An operating system kernel, MTOS, is utilized for newdevelopments and frees the programmer from concern with the details ofscheduling, memory management, and other system related tasks. MTOSwas chosen over a number of competing products due to support for boththe Intel and Motorola lines of processors. Code for processor basedembedded systems, a new quench protection monitor being the firstinstance, is written primarily in C with calls to operating systemservices made wherever possible. A new set of VAX based developmenttools (compilers, linkers), again supporting both processor lines, isutilized. Additionally, in-circuit emulators and debuggers which runon attached Personal Computers are used for testing and debugging at asource code level. All of these modern tools greatly increase theproductivity of programmers working on embedded systems, which controla large fraction of the most sophisticated accelerator equipment.SUMMARYUpgrades and modernizations of several aspects of the Fermilabaccelerator control system have been discussed. One of these, a newLocal Area Network, is essentially completed, and another, in themicroprocessor area, is fully utilizing new software tools in thedevelopmant of a prototype modern system. The other projects are beingpursued, but are farther from actual implementation.ACKNOWLEDGMENTSThe work described here represents the efforts of many members of theAccelerator Controls Department at Fermilab. Their hard work has ledto the successes which have occurred and those which are to come. Muchof this work was specified under the leadership of Dr. Dixon Bogert.

The Tevatron Control System - 1989

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