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The Computer Control System for the CESR B Factory C. R. Strohman, D

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The Computer Control System for the CESR B Factory C. R. Strohman, D The Computer Control System for the CESR B Factory C. R. Strohman, D. H. Rice and S. B. Peck Laboratory of Nuclear Studies Cornell University Ithaca, New York 14853' Abstract the strengths and weaknesses of our system and the different needs of the new system. Part of this process was defining the B factories present unique requirements for controls and scope of the control system, instrumentation systems. High reliability is critical to achiev­ ing the integrated luminosity goals. The CESR-B upgrade at A. Boundaries of the Control System Cornell University will have a control system based on the architecture of the successful CESR control system, which uses For a large design project, well defined boundaries are a centralized database/message routing system in a multi- essential. At the boundaries, the needs of other people must be ported memory, and VAXstations for all high-level control taken into consideration, and the design process requires functions. The implementation of this architecture will address communication between the designers and the users of the the deficiencies in the current implementation while providing control system. Within the boundaries, the control system the required performance and reliability. designers can do whatever is needed. We have defined the scope of the control system by defining interfaces for applica- I. INTRODUCTION tion programmers, instrumentation designers, and operators. Application programmers must be provided a complete, CESR-B is an upgrade to the existing CESR facility.1 well documented, set of functions which meet their needs. The major part of the upgrade is the addition of a second Programmers are not allowed to bypass these functions by storage ring in the existing tunnel. The two rings will operate using calls to lower-level routines. CESR uses approximately wifli asymmetric energies (3.5 GeV and 8 GeV) and will 35 functions. intersect within the CUEO detector. The design luminosity is Designers of instrumentation hardware are provided with 3xl0"cm V which will be achieved with 230 bunches in each a specification for constructing interfaces to the control system. ring. This includes mechanical, electrical, and protocol details. The control system for CESR-B is also an upgrade of the Recommendations that simplify the control system are includ- existing control system.2 The architecture is shown in figure ed, but not required. This encompasses things like avoiding 1. The MPM (Multi-Port Memory) contains the database and write-only registers and not having read operations change the is accessible by the high-level computers and the BCCs (Bus state of the system. Control Computers). The high-level computers are used to The actual implementation of the operator interface is a develop and ran programs which interface with the operators combination of efforts by both the application programmers and physicists to control and monitor the experiment The and the instrumentation designers. However, it is essential to BCCs manipulate and move data between the database and the know the needs of the operators when designing the control accelerator hardware. Both the MPM and the interface system, hardware are mapped into the memory space of the BCCs. They only transfer data when requested to by the high-level B. Special Requirements of Ike B Factory computers. It is important to remember the difference between the We need to know what makes CESR-B different from architecture of a system and how it is implemented. Within a CESR and how diese differences affect the architecture and well defined architecture, one can make hardware or software implementation of the control system, changes to improve some aspect of performance without The first question is how much larger will the new system affecting systems which are outside of the boundary of the be? At this early date, we do not have all of the details from control system. the various design groups (eg. vacuum systems, magnet systems), but we do have general numbers. Combining this II. DESIGN PROCEDURE information with the fact that the amount of equipment in the tunnel will approximately double, we determined that the new Having decided that the current CESR control system is comro1 sySIem wm ^^ roughly twice as many output control a suitable model for the B factory, we proceeded to analyze P0""5 **lhe current system. *Woik supported by the US National Science Foundation 110 LIHAC •2BOII9I-OOZ BUS CONTROL COMPUTER I "gey I PII DSIHJ pare5 CONTROL. ROOM BUS CONTOOL Figure 1. Control System Schematic We are planning to monitor a great deal more than we programs, uses 50% of one computer and 30% of the other. currently do. This will help minimize downtime either by This allows special applications (orbit measurements, energy indicating when a problem is developing or pointing to [he changes) to run in a timely fashion. The efficiency is achieved correct area when a malfunction occurs. With the increased by minimizing the layers of function calls required to commu­ monitoring and the additional equipment, we are assuming nicate with the hardware and by having processes hibernate about five times as many input control points. when they have requested that the BCCs move a lot of data. There will be several instrumentations systems which The system is simple and easily extended. We make require local processors. These systems will need a control minimal use of operating system and network functions. This system interface for passing processed data. They will also allows us to avoid 'black boxes'; pieces of software over need a connection for downloading and debugging. which we have no control. When we added a SUN computer for beam dynamics studies, it was trivial to move the subrou­ C. Strengths of the Existing CESR Control System tines that are provided to the application programmers. There is a single database. This allows us to avoid the Performance is a critical issue. When the operator turns programs and overhead which would be needed to maintain the a knob, there should not be a noticeable lag in the response. consistency of a distributed database. We run the CONSOLE program at 10 Hz. This is the The database and die interface hardware are memory program that accepts input from the operators and displays mapped into the address space of the BCCs. Simple 'move' results to them. Each time this program runs, it scans the instructions are used to access the database and the hardware. operator input devices, updates the controlled device, and The control bus can complete a data transfer to the farthest updates the operator's display. It takes about 7 milli-seconds interface crate in less than IS psec. Database accesses for each pass through this program. typically take less than 1 usee. The CESR control system makes very efficient use of the Several BCCs can work in parallel on a given transfer high-level computers. We currently use two V AXstation 3200 request For example, when reading magnet currents two computers. The normal application load, consisting of 14 computers are moving data, one for the east half of the ring 111 and the other for the west half. Three computers control the III. HARDWARE operator interface. The graphics display system provides fast and efficient A. High-Level Computers access to many graphics screens, both color and monochrome. It is accessable to all of the high-level computers. Data is sent CESR-B will probably use VAX computers for the major to it through a FIFO, so the high-level computers simply send high-level functions. The features of the VAX are that they data when they have it available. provide a reasonable development environment, they support Geographical addressing is used in the interface crates. priority scheduling of processes, and we are very familiar with Technicians do not need to set address switches on each card. them. We have shown that the control system operates We also insert and remove cards with the power on. comfortably on a VAX, and we expect that the heavier In the tunnel, the entire control system is contained with demands of CESR-B can be met by the newer generation a metallic exoskeleton for shielding. Feedthroughs are used VAXes. for connections to the controlled equipment. We are expecting As VAX performance improves, the inability to make a the electrical environment to be more severe in CESR-B. memory-mapped interface to the MPM becomes more of a bottle-neck. There is a two-stage plan to address this. First, D. Limitations of the Existing System we will make a 32 bit interface so that setting up the address register and moving the data becomes two operations, instead The CESR control system has worked extremely well for of four. If even more performance is needed, we will copy the over a decade. However, it does have limitations, most of read-only portion of the database into the VAX memory. The which stem from design decisions which were appropriate in VAXes will be clustered to facilitate disk sharing. the late 1970s. There may be other types of high-level computers for The address space on the control bus, which connects the special functions. Any computer that we can plug circuit interface crates in the tunnel to the bus control computers, is boards into can be interfaced to the control system. too small. Each control bus has an address space of 65 kwords. This is divided between 16 interface crates, with 16 B. Multi-Port Memory System slots per crate, yielding only 256 addresses per card slot. We do not have a simple local extension of the control The multi-port memory (MPM) will most likely be a bus. We need to allow designers to build control system VMEbus based system, although the Futurebus and any other interfaces into their equipment and have an easy way to contenders will be investigated.
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