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A System Approach to Data Processing Instrumentation and Control in a Scientific Research Center
A SYSTEH APPROACH TO DATA PROCESSING INSTRUUENTATION AND CONTROL IN A SCIENTIFIC
Hostafa A. Hassan Head of Control Laboratory Atomic Energy Establishment Cairo, Egypt
1.
R!S~~CH
CENTER
Kohamed A. Ghonaimy Assoc. Prof. of Electrical Engineering Ein Shams university Cairo, Egypt
INTRODUCTION
Hodern scientific experiments are demanding more and more sophisticated instruments and data handling equipment for their efficient execution, the subseq~ent computation and the proper display of the results. Refinements in these support equipment are also going at a very rapid rate making use of all the available improvements in technology. Horeover, some support equipment which is needed for a number of different experiments may be exactly the same and could be time shared in principle. Therefore, unnecessary duplication and frequent need for change to more sophisticated new models is usually encountered in many scientific institutes especially those which have a large diversified number of experiments. It is then of utmost importance to look at the whole problem from a new different angle as an integrated system. All types of experiments and computational needs are considered together. The demands as regard to the support equipment and the time scales of the experLBents are considered. Then an integrated information system ii developed in which expensive equipment and computing power could be shared between users. Data acquisition, processing and display requirements could be performed using a Single, time-shared, large computer with the appropriate memory size, speed and pheripherals. However such a system will be very expensive and its failure catastroplic. The advent of modern, low priced high speed minicomputers having performance comparable with large computers made ten years ago as well as integrated circuits has made the idea of establishing information networks a feasible task. However the specific characteristics of the 16 bit minicomputers such as word length and maximum memory size per computer should be taken in consideration in system design. Such a concept would result in an increased availability and easy expandability. Horeover the network will be, to a certain extent, immune from the dangerous threat of becoming outdated.
late physical parameters with varying accuracy and at different rates. In engineering experiments parameters such as temperatures, flows, pressures, etc are usually measured. Tran.ducer. used give, in general, low .ignal. of analog form. which are then operated upon by appropriate signal conditioning equipment and finally recarded for further off-line preparation on data processing machine.. To relieve the experimentator from this tedious and time consuming process of preparing his analog data for the digital computer, special equipment has been produced to automate this process by operating directly on the signal and preparing the output in the form of punched paper or magnetic tape. In physics experiments quantities such as pulse amplitude and rate, and time intervals between events are analyzed and grouped together, then outputted in a form suitable for further off-line processing (e.g. in multichannel analyzer). Host of these expensive equipment are usually tied to a specific experiment and cannot serve others. A computer-based system can make full advantage of the sLBilarity of the needs for experiments by time sharin! the capabilities of a system of computer. and some of the measuring units between a number of different experiments. Tbi. will result in both a price reduction and performance improvement. 2.2. High Speed Real-Time proce.sing and Control In .ome experimental facilitie. it i. e •• ential to acquire and analyze data at a rapid rate then according to the outcome of the.e analy.e., generate the appropriate control .ignal. which execute. the experiment in the desired manner. Typical examples are, Nuclear and chemical reactors, particle accelerators and experiment. involving tran.ient.. Voreover, rapid analysi. and display of appropriate data allows the experimentator to cbange tbe cour.e of hi. 'pecific experiment to .uit hi. needs. This results in reducing the time and price of executing a successful experiment. 2.3. Reliability and Vaintainability
2.
WHY SYSTnt A.PPROACH?
It may appear at the first glance that the use of a computer to serve a number of experiments Till result in a reduction in reliability. This may
2.1. Similar Instrumentation Requirements All scientific experiments measure and manipu-
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be true if the research center will use separate, isolat.d computers for serving his experiments. However, when the computers are interconnected to form a network the reliability will definitely increase. Regarding the maintainability problem it is evident that the use of computers will facilitate maintenance since instead of using a large variety of different types of special purpose equipment, we shall concentrate only on computers with its modular design and relative ease of maintenance once a group of qualified engineers have been assigned and trained for the job. 2.4. Capabilities of a Computer Network In general, a computer within the network would be more efficiently utilized than outside. This means that extra computing tUae and memory space could be utilized by other computers. If the planned network is being designed before any computers are installed, then it is possible to optimally utilize all the computers and take into consideration the requirements of the network when ordering the individual machines. However, in the case of existing separate computers ~ already in operation the system design can give the extra capabilities which result from the interconnection and which will depend on the type of existing hardware. In a computer network, •• i.ntili'c c computations could be always performed as background work for some of the lightly loaded computers either in a batch processing mode or on multiterminal conversational basis. 2.5. Expansion and up-dating of the Network A computer network is expected to be expensive, and require a high state of technical know-how. Therefore, it is reasonable to implement it on a number of steps. The first step could be the implementation of a single real-time computer serving a number of experUaents. After a reasonable state of technical know-how is acquired, other similar computer systems could be simultaneously implemented. The interconnection stage could then start after an initial system study justifies the network. This stage may involve the installation of an executive computer for the network f'ollow.eil by COllllllon lIerlph'elt&I&. The next stage may then be the interconnection to a high speed large scientific computer, to increase the numerical processi., power, through appropriate communication links. Such an approach bears certain similari~ies with power system interconnection schemes. The advantages of this approach is its ability to absorb any new developments in computer technology and concepts. Figure (1) shows a possible implementation scheme. 3.
SYNTm:3IS OF THE COMPUTER NErWORK
3.1. Requirements and Computer Configuration for Different Types of Experiments In this section the general requirements for
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these types of experiments, typical for a large research establishment .ill be given together with the conventional and co.puter-b.sed equipment needed for executing .uch experI.ents. Our aim here i. to establish a general outline which act. as a means of comparison between different configurationsJ actual comparison in te~s of prices could only be executed when the exact nature of the experiments and it. future developments are known. Thenaal ExperUaents, This type of experiments is usually conducted to measure thermal and hydraulic phenomena in heat transfer apparatus. The following types of transducers are usually installedJ flow, temperature pressure and phase state transducers. The outputs of such transducers are low electrical signals with relatively slow variations. Typical magnitude scales are milli and micro volts, and time scale is seconds and minutes. The number of transducers usually ranges from tens to hundreds. The outputs of these transducers are usually recorded and processed off-line on digital computers. The instrumentation needed for such experiments are: signal conditioning amplifiers, chart.recorders, relay scanners, digital voltmeters and digital printout equipment. Non-computer- based digital data acquisition systems are also available. A minimum computer-based system for such experiments could constitute a 4K CPU with a high resolution low speed analog subsystem. Physics Experimentsl A great number of physics experUaents are concerned with the identification of the energy of nuclear particles. In this type of experiments pulses are analyzed for their magnitudes or their time of arrival. The basiC in8truments for thi8 research are crystal or semiconductor particle detectors and mul tichanne 1 analyzer8. pulses coming out fr.OIR the detectors have Qmplitudes in the order of millivolts and an average repetition rate of KC/s to KC/8. The number of such detectors involved in physics experfaent8 ranges from one to ten. A multichannel analyzer consist8 of a pulse -'plitude-to-code cODve'r.tiel'J, a core memory yhose 8ize depend8 on the pu18e amplitude re80lution with 4 to 8 K being the m08t popular, spectrum display unit, and printout eqUipment. Printout data are further analyzed using digital computers. Some phy8ics experiments might need the adjustment of the transducer pOSitions as a function of the data collected, therefore requiring a feed back control system. A minimum computer-based configuration could be an 8K CPU yith a fast ADC and a cathode ray display unit. Dynamics and Control EXperiments: These experiments are aimed at studying the dynamic behaviour of control systems and the checking of control all()rithms developed using advanced concepts. Such experiments are usually of a closed loop nature involving manipulation of control variables. The transducers used are of different types and include those used in thermal experiments as yell as other process variable 8uch as gas chromatographs. In general, the accuracy requirements are les8 demanding than physics and
thermal exper~ents. However, the models are usually of more complex nature. Control variable manipulations could be performed using analog-type controllers or using a digital computer. Analog-type controllers are usually limited to situations in which the optimal controls are of a stmple nature such as m*ltiplying each measUred variable by aCDa~ and summing to develop the control signals. Optimum estimation and on-line identification for the purpose of control are very difficult to implement without the exi*tance of on-line digital computers. A minimum computer configuration for such experiments is a 12K CPU with analog inputs and outputs, and digital inputs and outputs together with a real-time operating system which allows close man-machine communication. Table 1
Conventional datahandling system
Computer-based system
Thermal
Chart recorders, voltmeter (D. V.11.), relay scanners, printout and digital data recording systems.
High resolution, low speed analog subsystem and 4K CPU.
MUltichannel ampli tude and time analyzers, counters, display and output equipment.
Fast ADC with an 8K CPU and display.
Analog recorders controllers, D. V.Il., solid state scanners, sequence control proerummers, and printout equipment.
Real-time interface with closed loop capabi lities and 12K CPU with operator/ machine communication facilities.
di~ital
iii) Address information I destination address lines carry the code of the requested computer or common device and are fed from the computer which holds the common bus (aaster) to locate the slave computer or Common peripheral. iv) Bus grant line which carries the code as given by the priority network of the computer that will hold the common bus.
-----------_._---Physics
DIn_ics and control
3.2
i) Priority information and bus request , each computer has direct and independent access to the executive computer (Z.o.) through few bus lines conveying to it information regarding the type of and reason for information transfer. The E.C. will then allocate the appropriate priority for acquiring the bus. The types of information transfer could be programs, executive information or data and the reason might be emergency or normal resouree sharing. The priority control network connected to the Z.C. takes part in the implementation of the priority and the control of the Common bus. ii) Data interchanged, lines used for bidirectional transfer of data between two computers or a computer and a common device.
Summary of support requirements Experiment type
twisted pair cable. Each computer is connected to the bus through an interface card. Through this interface the following information could be exchanged between the different computers using the bus wiresl see Fig. (3),
v) Control and synchronization information exchanged between the priority network and the computers involved. This includes direction of transmission, bus ready Signal, end of word signal and end of range signal. It should be noted that the Z.C. is the manager for all intercomputer and Common peripheral activities. All the computers in the network report their status to the E.C. and according to information on the loading of each member it will manage the resource sharing activities. When the common bus is not used by intercomputer transfers of higher priority the E.C. is automatically the bus master. Another function of the E.C. is the communication between the integrated network and another large high speed scientific computer which is usually at a considerable distance from the network and which will be used to solve larger problems. The transmission will be done over an exchange telephone line with modems interfaced through asynchronous line controllers to the computers. Local equipment between a computer and the experiments under control consists of the measuring, controlling and display equipment for the exper~ents. It is interfaced to the computer and to the Common bus through adequate links with the possibility of manual of automatic switch over, in case of local computer failure. Local peripherals are those low cost input-output units which are needed for the computer operation and used so frequently that they YOuld heavily load the bus if connected to it, typical devices are teletypes, fast paper tape read and punch, small mass stores and for some experiments even
Integrated Information System
A possible scheme for interconnecting the different computers involved in an integrated information network is shown in Fig. (2). This is a single level, equal bases, parallel structure with an executive computer holding the management function. It resembles a multiprocessor co.puter system, and was thought more adequate than other known configurations such as the hierarchial, the exchan~e, and the cross connected configurations (1),(2) since it offers greater simplicity and case in expandability. The reliability of the parallel bus transmission over the small distances involved (max. 500 meters) is considered adequate. Information, control and synchronization signals are transferred in parallel over the common bus which is for seen as a multi-wire
483
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a magnetic tape. The peripherals connected to the common b~s are large capacity discs, card readers and high speed line printers. To increase the backgro~d comp~tation capabilities of the network a dedicated mini-computer with hardware floating point aritbm.tic capabilities might be added. A block diagram for a typical interface card for connecting a computer to the Common b~. i. • hown in Fig. (4). When a computer request. interconnection with another comp~ter or peripheral it has first to i.sue a req~est to the E.C. Thi. i. done through the non-ahared bus req~est and priority information wires. When the addre •• presented to the decoder D1 i. fo~d to be that of the E.C. then a part of the data in the o~tp~t register is transmitted through gate G 1 to the priority information lines. If the E.C. grant. the b~s to the requesting comp~ter, on priority bases and thro~gh the priority network, a code is propagated along the bus grant lines which is decoded by Dz to interr~pt the master Computer through line B. This is needed at the beginning of transmission to alert the soft-ware for defining the memory blocks and initializing the direct memory acces.(DHA). When this i. complete a signal from the computer sets the ready flip-flop. The master will subsequ.ntly send the address of the req.. st'. computer which will pass through gates Gz to the bus address lines ~til it is picked by the requested computer or slave by means of the decoder D3. This action interrupts the slave computer by means of line S which in turn initializes its DKA and turn on its ready flip-flop. Referring to the timing diagram of Fig. (~), note that when the bus is granted a pulse train is generated by the priority network. First, the synchronization pulse bus ready-l is propagated along the corresponding bus wire and enters the master through gate G3 when the ready flip-flop is set. This is a request for a word trausfer by the DUA, according to which a DKA cycle is started and when the word is transferred an operation complete pulse will pass through gate Gr to the priority network. Therefore the first word is now in the output buffer. Through gate G4 of the master and GS of the slave computer information is transferred from the output buffer of the master to the input buffer of the slave gated by bus ready-2 which is isaued by the priority network after the latter receives the above mentioned operation complete pulae. The bus ready-2 pulae will also requeat a DHA cycle from the slave through gate G6. When the DHA inputs the word it give an operation complete pulae. This second operation complete pulse will pass through gate Gg to the priority network indicating the succesalul transter of one word. If the master computer is still granted the bus then successive word transfers will occur ~til an end ot range pulse from the master resets the ready flip-tlop. The E.C. could be notified through the priority information and bus request linea. However if the bua is taken from the master betore the end of range the ready flip-flop will remain aet and transter
485
will be resumed as soon as the bus is granted back. In the above realization of the interface it waa assumed that the master computer will always be transmitting. Appropriate measures should be taken by the E.C. to inaure that and to switch mastership between computera whenever needed. Another alternative is to include additional gating on some of the interface registers to allow bidirectional transfer from the master • 3.3
Coordination of the
Intercomp~ter
Activitiea
In thia section the part of the operating software which is directly connected with the intelration of the network and the intercomputer activities will be discu.sed. It i. assumed that all the minicomputer. involved have a real time operating system, with different degrees of sophistication, aupplied by the man~facturer and that appropriate change. have to be made in them to cope with the needs of the network. In general, intercomputer activities involve transfer of status and control worda, data, symbolic programs and machine language programs. It also includes back-up activities in case one computer fails and it is decided through the E.C. to distribute its important tasks among other Computers. The state of each computer regarding core storage usage and central processor utilization is reported to the E.C. This is possible through dividing each computer memory into pages and keeping the E.C. regularly notified on the number of ~used pages in each computer. The amo~t of central processor utilization could be measured by the time interval it spends looping in its sheduler each second. This information is stored in a status table arranged at specific locations in the E.C. memory. Knowing the above parametera the E.C. will manage the load distribution and resource sharing; however, the actual job scheduling and execution is left for the local executives. All intercomputer requests will be first reported to the E.C. which will choose the moat appropriate computer to handle the job of the requesting computer, the criteria might be equal loading or faster throughout. A summary of the steps involved in the network management ia given below, a) The requesting computer comm~icatea a tixed amo~t of information specifying its demands to a fixed bufter in the memory of the E.C. The latter will then use the status table to choose the most appropriate computer to handle the request. b) The E.C. transmits the results of its analysis to the requesting computer which is received at a specific butfer in the memory of the latter. c) The requesting computer will transmit the job to the chosen computer through their respective D.B.A. When the transmission is completed an interrupt aignal for both computers is established. For the receiving computer it notifies its local executive that an additional job is received and has to be scheduled for execution.
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If the r.e celved job is in machine language and it involve. a change in the base sector addresses due to the transfer, the local executive will have to correct for any confusion that may arise due to the addressing modes of the l6-hit minicomputers (3). To make this correction easier it might be necessary to separate progr~s from data and divide the base sector to section. that are dynamically alloted to the transmitted programs. The data transmitted does not need to undergo any correction and would be directly available for processing. The transmission Complete interrupt would inform the sending computer that transfer ha. _lIleti, _.uge ah...]. be cl14lcked. uti ..teara,. tree.d _d r_aed. d) The structure of the messages transmitted should have a fixed header containing key information such as the source computer, type of information transferred, requested action on the transmitted information; followed by the message proper and then checking data, After the receiver computer analyzed the message transferred for e~ror. i\ shed~leB processing or requests retransmission through the E.C. Communication between the network computers and the E.C. includes other types of information transfers such as I Failure reporting and status reporting. This is clear from the interrupt analysis flow chart shown in Fig. (6a). The status information is first identified as to its origin and then transferred to the corresponding slot in the status table. For failure reporting highest priority is given in transmission and analysis. Then the bus is granted for the back-up action and end of transmission interrupt would cause the E.C. to respond by giving the bus to the next request in the bus queue table. The part of the memory map of the E.C. holding the network management progr&ms is shown in Fig. (6b). 4. 4.1
SYST.Df ANALYSIS
Preliminary Objectives of the Network
The main two criteria for network evaluation are a) I{aximum utilization of available hardware which could be measured by the computational throughput and tbe response time. b) The increased reliability and fail-soft characteristics. This could be measured by the reduction of overall performance as a result of an element failure. The above two requirements affect the syste. integration methods both in software and hardware. The first point is mainly a function of the efficiency of the network executive .oftware and how it bandIes the available resources with minimum managerial overhead. The second point is a combined function of both system hardware architecture and software sophistication. For example, if an important experiment has to be serviced continuously then an automatic link should be available to connect it to the bus in case of local computer failure. Another aspect is the degree of software distribution ~ong local and Common back-up storage~
487
'bho ,N ...ca Id eo,ie. of im,oE1..~t hDtt.iculIt in more than one back-up storage, which are available for retrieval and use. That is to say duplication and automatic switch over. 4.2
Increase of System Capabilities a. a Result of Integration
The presence of communication pathes &mong the different computers of the network would lead to the availability of more computational power for each experiment. This is mainly due to the difference in the timing of peak loads on the different machines. Computers doing control functions are loaded heavily during transients while other computers doing data acquisition for physics experiments are usually loaded more heavily when the experimental facilities are at steady state. Hypothetical loading curves are shown in Fig. (7). Consider the example of three computers used for three types of experiments as discussed ill section 3.1. If the computers were not connected then we would use l6K memory for the control Computer, 12K memory for the physics computer, and 4K memory for the heat transfer computer. However, if we have them connected in a network then it would be possible to reduce the memory capacity of these machines to 12K, 8K and 4K respectively making use of the time difference in the peak occurrence. When there will be more computers serving different experiments on the same experimental facility the difference in loading cycles would be then available tor conversational computation jobs. It is also not uncommon that some experiments are not running for few days, while setups are changed. 4.3
Bottlenecks and System Performance Evaluation
A basic bottleneck in the computer network is clearly the Common bus interconnecting the Computers and peripherals. If the bus cannot handle the data traffic quickly then memory space in different computers will be tied for longer time (e.g. when a computer wants to transfer data to common (lisc unit or to the line printer). This means t11Ut a s low bus unit may nece ssi tate the increase in core memory capacity to hold the output data for a longer time until the bus is free for the transfer. If the system becomes bus limited then we have to resort to the exchange approach for interconnecting the Computers and peripherals in a network. Other bottlenecks may be the line printer and the disc unit when the bus unit is capable of a high transfer rate and the utilization factor for each of these units is high. For the ddsc this means that its access ttroe should match the transfer rate over the bus, and for the line printer an appropriate buffer size should be used. An obvious remedy for this situation is to h"ve more than one disc unit or line printer, so that a queue will not build up in the core memories of the working computers. Queuing theory could be used to get a quantitative measure for the bus-unit loading based on typical figures for traffic volume. The bus
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unit situation could be visualized as a singleserver qu!ue 4 as shown in Fig. (S). Let n be the average arrivals per second and be the service time of an item (in this case the complete transfer of a word from one computer to another one or a common peripheral), and ~ be the standard deviation of all service times. The number of items yaiting at a given time for service is wand the number of items in the system both yaiting service or being serticed at a given time is q. If P is the facility utilization, then in the steady state
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This formul~ applies to exponential interarrival times, any distribution of service times, and any rule for the selection of the next item to be serviced provided that it does not depend on the service time (e.g. first-in first-out FIFO). For transfer over the bus unit the most critical type of transfer is from the computers to the disc units and vice versa. Assume that there are four computers and one Common disc in the netyork; and that we transfer, on the average, 1 K words from each computer to the disc per sec. An average access time for the disc of 30 msec is considered and an average transfer time of 20 usec. For this case the service time for an item of 1 K yords yill beJ service time - 30 + 1000x20 - 50 msec. Since there are four computers, the average arrivals per sec. ~re assumed to be n • 4. The facility utilization p is then, p
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These figures indicate that the transfer over the bus unit in the above mode will not load the system [4] • It should be noted that the above analysis are very rough estimates; more precise analysis could only be done using simulation methods combined with some statistical information, if available, regarding the modes of data transfers between the elements of the net york as handled by the proposed software operating system. 5.
DESCRIPTION OF A PLANNED NETWORK
In the ARE Atomic Energy Establishment, a center for basic scientific and applied research in Nuclear Engineering, the idea of using computers to support experiments and establishing an
489
integrated information netyork came gradually since 1969. The stimulating factor was the appearance of small, reasonably priced, fast, and highly reliable computers using integrated circuits. It took about tyO years to acquire and make operational an H-3l6 computer, from Honeyyell Information Systemf, which yas planned for on-line control experiments for nuclear reactors. This computer has 1.6 usec. cycle time, 16 bit yord, and 16 K yord of core memory, a ..all disc mass store of la2 K yord is also available. Input-output devices are a Teletype and a fast paper tape read and punch. The real time interface to serve the control experiments involves analog and digital input-output subsyst. .s, as yell as additional interrupt facilities. The reactor is scheduled to go under computer control early 1973. The design of a fey hardyare units such as an operator communication desk as yell as the application softyare yhich involved additions to the manufacturer's softyare capabilitie. ya. developed by an in-house group. After acquiring the above computer, interest of other research groups in the use of computers to support their experiments yas raised. Physicists involved in spectrometry and neutron diffraction studies as yell as thermal engineers doing york on heat transfer studies yanted to computerize their experiments. A pulse high analysis demonstration yas made by interfaCing a locally designed ADC to the IT-3l6 and using an ordinary scope for spectrum display. A second computer yas then planned for 1973 and the choice yas for an H-716 from the same manufacturer. A ruling factor in its favour yas the softyare compatability yith the existing one. This new computer has a tyO times shorter cycle time and a D.K.A. yhereas the H-316 has only a DHC (Direct HultipleEControl). It has also some useful hardyare additions to make it more poyerful in real time applications, such as a standard fast clock and stack facilities as well as a more poyerful operating softYare. This computer yill serve, for the time being, the physics and thermal experiments on time sharing basis. parallel connection betyeen the tyO computers yill be tried using an interface along the same lines with that discussed in this paper as yell as the additions needed to the operating system for both computers to manage the intercomputer activities. The distance between the tyO computers yill be about 200 meters and parallel transmission yill be used. This project is planned for 1973-1974. A large scientific computer ICL-1905 at Cairo Ubiversity is available to provide large scientific data processing. Communication b9tween this computer and one of the local computers over a telephone line will be attempted. The operating system of the ICL-1905 could support ASCII terminals and the expected rate of transmission would be 600-1200 bauds. The next step is the organization of a Common bUB network and the installation of the executive computer, which is planned for 1975. EXpensive equipment such aB large cap~city multitrack disc stores and line printer will be connected to the network after the executive computer
is introdu ced. The execut ive comput er will support about eight teletyp es connec ted direct ly to it which will serve as conver sationa l comput ation termin als in Basic languag e for the labora tories and will also contro l the transm ission of more involve d program s in FORTRAN over the telephone line to the scient ific comput er and receiving the result s back for printin g. 1
REFERENCES Franz, L. Alt, Worris Rubino ff, Editor s, A~ances in compu ters, Vol. 4, Sectio n on Multip le Comput er System s, Academic Press, New York 1963.
2
C.G. Bell and Al., Comput er networ ks, Compu ter, septem ber/Oc tober 1970.
3
J.J. Morris , What to expect when you scale
down to a min*c~p.bet1,Control Engine ering, Septem ber 1970. 4
James Martin , Design of a real time comput er System ,Prentt ee-Hal l Inc., Englew ood Cliffs . New Jersey 1967.
490
Hostafa A. Hassan Head of Control Laboratory Atomic Energy Establishment Cairo, Egypt
1.
R!S~~CH
CENTER
Kohamed A. Ghonaimy Assoc. Prof. of Electrical Engineering Ein Shams university Cairo, Egypt
INTRODUCTION
Hodern scientific experiments are demanding more and more sophisticated instruments and data handling equipment for their efficient execution, the subseq~ent computation and the proper display of the results. Refinements in these support equipment are also going at a very rapid rate making use of all the available improvements in technology. Horeover, some support equipment which is needed for a number of different experiments may be exactly the same and could be time shared in principle. Therefore, unnecessary duplication and frequent need for change to more sophisticated new models is usually encountered in many scientific institutes especially those which have a large diversified number of experiments. It is then of utmost importance to look at the whole problem from a new different angle as an integrated system. All types of experiments and computational needs are considered together. The demands as regard to the support equipment and the time scales of the experLBents are considered. Then an integrated information system ii developed in which expensive equipment and computing power could be shared between users. Data acquisition, processing and display requirements could be performed using a Single, time-shared, large computer with the appropriate memory size, speed and pheripherals. However such a system will be very expensive and its failure catastroplic. The advent of modern, low priced high speed minicomputers having performance comparable with large computers made ten years ago as well as integrated circuits has made the idea of establishing information networks a feasible task. However the specific characteristics of the 16 bit minicomputers such as word length and maximum memory size per computer should be taken in consideration in system design. Such a concept would result in an increased availability and easy expandability. Horeover the network will be, to a certain extent, immune from the dangerous threat of becoming outdated.
late physical parameters with varying accuracy and at different rates. In engineering experiments parameters such as temperatures, flows, pressures, etc are usually measured. Tran.ducer. used give, in general, low .ignal. of analog form. which are then operated upon by appropriate signal conditioning equipment and finally recarded for further off-line preparation on data processing machine.. To relieve the experimentator from this tedious and time consuming process of preparing his analog data for the digital computer, special equipment has been produced to automate this process by operating directly on the signal and preparing the output in the form of punched paper or magnetic tape. In physics experiments quantities such as pulse amplitude and rate, and time intervals between events are analyzed and grouped together, then outputted in a form suitable for further off-line processing (e.g. in multichannel analyzer). Host of these expensive equipment are usually tied to a specific experiment and cannot serve others. A computer-based system can make full advantage of the sLBilarity of the needs for experiments by time sharin! the capabilities of a system of computer. and some of the measuring units between a number of different experiments. Tbi. will result in both a price reduction and performance improvement. 2.2. High Speed Real-Time proce.sing and Control In .ome experimental facilitie. it i. e •• ential to acquire and analyze data at a rapid rate then according to the outcome of the.e analy.e., generate the appropriate control .ignal. which execute. the experiment in the desired manner. Typical examples are, Nuclear and chemical reactors, particle accelerators and experiment. involving tran.ient.. Voreover, rapid analysi. and display of appropriate data allows the experimentator to cbange tbe cour.e of hi. 'pecific experiment to .uit hi. needs. This results in reducing the time and price of executing a successful experiment. 2.3. Reliability and Vaintainability
2.
WHY SYSTnt A.PPROACH?
It may appear at the first glance that the use of a computer to serve a number of experiments Till result in a reduction in reliability. This may
2.1. Similar Instrumentation Requirements All scientific experiments measure and manipu-
481
be true if the research center will use separate, isolat.d computers for serving his experiments. However, when the computers are interconnected to form a network the reliability will definitely increase. Regarding the maintainability problem it is evident that the use of computers will facilitate maintenance since instead of using a large variety of different types of special purpose equipment, we shall concentrate only on computers with its modular design and relative ease of maintenance once a group of qualified engineers have been assigned and trained for the job. 2.4. Capabilities of a Computer Network In general, a computer within the network would be more efficiently utilized than outside. This means that extra computing tUae and memory space could be utilized by other computers. If the planned network is being designed before any computers are installed, then it is possible to optimally utilize all the computers and take into consideration the requirements of the network when ordering the individual machines. However, in the case of existing separate computers ~ already in operation the system design can give the extra capabilities which result from the interconnection and which will depend on the type of existing hardware. In a computer network, •• i.ntili'c c computations could be always performed as background work for some of the lightly loaded computers either in a batch processing mode or on multiterminal conversational basis. 2.5. Expansion and up-dating of the Network A computer network is expected to be expensive, and require a high state of technical know-how. Therefore, it is reasonable to implement it on a number of steps. The first step could be the implementation of a single real-time computer serving a number of experUaents. After a reasonable state of technical know-how is acquired, other similar computer systems could be simultaneously implemented. The interconnection stage could then start after an initial system study justifies the network. This stage may involve the installation of an executive computer for the network f'ollow.eil by COllllllon lIerlph'elt&I&. The next stage may then be the interconnection to a high speed large scientific computer, to increase the numerical processi., power, through appropriate communication links. Such an approach bears certain similari~ies with power system interconnection schemes. The advantages of this approach is its ability to absorb any new developments in computer technology and concepts. Figure (1) shows a possible implementation scheme. 3.
SYNTm:3IS OF THE COMPUTER NErWORK
3.1. Requirements and Computer Configuration for Different Types of Experiments In this section the general requirements for
482
these types of experiments, typical for a large research establishment .ill be given together with the conventional and co.puter-b.sed equipment needed for executing .uch experI.ents. Our aim here i. to establish a general outline which act. as a means of comparison between different configurationsJ actual comparison in te~s of prices could only be executed when the exact nature of the experiments and it. future developments are known. Thenaal ExperUaents, This type of experiments is usually conducted to measure thermal and hydraulic phenomena in heat transfer apparatus. The following types of transducers are usually installedJ flow, temperature pressure and phase state transducers. The outputs of such transducers are low electrical signals with relatively slow variations. Typical magnitude scales are milli and micro volts, and time scale is seconds and minutes. The number of transducers usually ranges from tens to hundreds. The outputs of these transducers are usually recorded and processed off-line on digital computers. The instrumentation needed for such experiments are: signal conditioning amplifiers, chart.recorders, relay scanners, digital voltmeters and digital printout equipment. Non-computer- based digital data acquisition systems are also available. A minimum computer-based system for such experiments could constitute a 4K CPU with a high resolution low speed analog subsystem. Physics Experimentsl A great number of physics experUaents are concerned with the identification of the energy of nuclear particles. In this type of experiments pulses are analyzed for their magnitudes or their time of arrival. The basiC in8truments for thi8 research are crystal or semiconductor particle detectors and mul tichanne 1 analyzer8. pulses coming out fr.OIR the detectors have Qmplitudes in the order of millivolts and an average repetition rate of KC/s to KC/8. The number of such detectors involved in physics experfaent8 ranges from one to ten. A multichannel analyzer consist8 of a pulse -'plitude-to-code cODve'r.tiel'J, a core memory yhose 8ize depend8 on the pu18e amplitude re80lution with 4 to 8 K being the m08t popular, spectrum display unit, and printout eqUipment. Printout data are further analyzed using digital computers. Some phy8ics experiments might need the adjustment of the transducer pOSitions as a function of the data collected, therefore requiring a feed back control system. A minimum computer-based configuration could be an 8K CPU yith a fast ADC and a cathode ray display unit. Dynamics and Control EXperiments: These experiments are aimed at studying the dynamic behaviour of control systems and the checking of control all()rithms developed using advanced concepts. Such experiments are usually of a closed loop nature involving manipulation of control variables. The transducers used are of different types and include those used in thermal experiments as yell as other process variable 8uch as gas chromatographs. In general, the accuracy requirements are les8 demanding than physics and
thermal exper~ents. However, the models are usually of more complex nature. Control variable manipulations could be performed using analog-type controllers or using a digital computer. Analog-type controllers are usually limited to situations in which the optimal controls are of a stmple nature such as m*ltiplying each measUred variable by aCDa~ and summing to develop the control signals. Optimum estimation and on-line identification for the purpose of control are very difficult to implement without the exi*tance of on-line digital computers. A minimum computer configuration for such experiments is a 12K CPU with analog inputs and outputs, and digital inputs and outputs together with a real-time operating system which allows close man-machine communication. Table 1
Conventional datahandling system
Computer-based system
Thermal
Chart recorders, voltmeter (D. V.11.), relay scanners, printout and digital data recording systems.
High resolution, low speed analog subsystem and 4K CPU.
MUltichannel ampli tude and time analyzers, counters, display and output equipment.
Fast ADC with an 8K CPU and display.
Analog recorders controllers, D. V.Il., solid state scanners, sequence control proerummers, and printout equipment.
Real-time interface with closed loop capabi lities and 12K CPU with operator/ machine communication facilities.
di~ital
iii) Address information I destination address lines carry the code of the requested computer or common device and are fed from the computer which holds the common bus (aaster) to locate the slave computer or Common peripheral. iv) Bus grant line which carries the code as given by the priority network of the computer that will hold the common bus.
-----------_._---Physics
DIn_ics and control
3.2
i) Priority information and bus request , each computer has direct and independent access to the executive computer (Z.o.) through few bus lines conveying to it information regarding the type of and reason for information transfer. The E.C. will then allocate the appropriate priority for acquiring the bus. The types of information transfer could be programs, executive information or data and the reason might be emergency or normal resouree sharing. The priority control network connected to the Z.C. takes part in the implementation of the priority and the control of the Common bus. ii) Data interchanged, lines used for bidirectional transfer of data between two computers or a computer and a common device.
Summary of support requirements Experiment type
twisted pair cable. Each computer is connected to the bus through an interface card. Through this interface the following information could be exchanged between the different computers using the bus wiresl see Fig. (3),
v) Control and synchronization information exchanged between the priority network and the computers involved. This includes direction of transmission, bus ready Signal, end of word signal and end of range signal. It should be noted that the Z.C. is the manager for all intercomputer and Common peripheral activities. All the computers in the network report their status to the E.C. and according to information on the loading of each member it will manage the resource sharing activities. When the common bus is not used by intercomputer transfers of higher priority the E.C. is automatically the bus master. Another function of the E.C. is the communication between the integrated network and another large high speed scientific computer which is usually at a considerable distance from the network and which will be used to solve larger problems. The transmission will be done over an exchange telephone line with modems interfaced through asynchronous line controllers to the computers. Local equipment between a computer and the experiments under control consists of the measuring, controlling and display equipment for the exper~ents. It is interfaced to the computer and to the Common bus through adequate links with the possibility of manual of automatic switch over, in case of local computer failure. Local peripherals are those low cost input-output units which are needed for the computer operation and used so frequently that they YOuld heavily load the bus if connected to it, typical devices are teletypes, fast paper tape read and punch, small mass stores and for some experiments even
Integrated Information System
A possible scheme for interconnecting the different computers involved in an integrated information network is shown in Fig. (2). This is a single level, equal bases, parallel structure with an executive computer holding the management function. It resembles a multiprocessor co.puter system, and was thought more adequate than other known configurations such as the hierarchial, the exchan~e, and the cross connected configurations (1),(2) since it offers greater simplicity and case in expandability. The reliability of the parallel bus transmission over the small distances involved (max. 500 meters) is considered adequate. Information, control and synchronization signals are transferred in parallel over the common bus which is for seen as a multi-wire
483
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a magnetic tape. The peripherals connected to the common b~s are large capacity discs, card readers and high speed line printers. To increase the backgro~d comp~tation capabilities of the network a dedicated mini-computer with hardware floating point aritbm.tic capabilities might be added. A block diagram for a typical interface card for connecting a computer to the Common b~. i. • hown in Fig. (4). When a computer request. interconnection with another comp~ter or peripheral it has first to i.sue a req~est to the E.C. Thi. i. done through the non-ahared bus req~est and priority information wires. When the addre •• presented to the decoder D1 i. fo~d to be that of the E.C. then a part of the data in the o~tp~t register is transmitted through gate G 1 to the priority information lines. If the E.C. grant. the b~s to the requesting comp~ter, on priority bases and thro~gh the priority network, a code is propagated along the bus grant lines which is decoded by Dz to interr~pt the master Computer through line B. This is needed at the beginning of transmission to alert the soft-ware for defining the memory blocks and initializing the direct memory acces.(DHA). When this i. complete a signal from the computer sets the ready flip-flop. The master will subsequ.ntly send the address of the req.. st'. computer which will pass through gates Gz to the bus address lines ~til it is picked by the requested computer or slave by means of the decoder D3. This action interrupts the slave computer by means of line S which in turn initializes its DKA and turn on its ready flip-flop. Referring to the timing diagram of Fig. (~), note that when the bus is granted a pulse train is generated by the priority network. First, the synchronization pulse bus ready-l is propagated along the corresponding bus wire and enters the master through gate G3 when the ready flip-flop is set. This is a request for a word trausfer by the DUA, according to which a DKA cycle is started and when the word is transferred an operation complete pulse will pass through gate Gr to the priority network. Therefore the first word is now in the output buffer. Through gate G4 of the master and GS of the slave computer information is transferred from the output buffer of the master to the input buffer of the slave gated by bus ready-2 which is isaued by the priority network after the latter receives the above mentioned operation complete pulae. The bus ready-2 pulae will also requeat a DHA cycle from the slave through gate G6. When the DHA inputs the word it give an operation complete pulae. This second operation complete pulse will pass through gate Gg to the priority network indicating the succesalul transter of one word. If the master computer is still granted the bus then successive word transfers will occur ~til an end ot range pulse from the master resets the ready flip-tlop. The E.C. could be notified through the priority information and bus request linea. However if the bua is taken from the master betore the end of range the ready flip-flop will remain aet and transter
485
will be resumed as soon as the bus is granted back. In the above realization of the interface it waa assumed that the master computer will always be transmitting. Appropriate measures should be taken by the E.C. to inaure that and to switch mastership between computera whenever needed. Another alternative is to include additional gating on some of the interface registers to allow bidirectional transfer from the master • 3.3
Coordination of the
Intercomp~ter
Activitiea
In thia section the part of the operating software which is directly connected with the intelration of the network and the intercomputer activities will be discu.sed. It i. assumed that all the minicomputer. involved have a real time operating system, with different degrees of sophistication, aupplied by the man~facturer and that appropriate change. have to be made in them to cope with the needs of the network. In general, intercomputer activities involve transfer of status and control worda, data, symbolic programs and machine language programs. It also includes back-up activities in case one computer fails and it is decided through the E.C. to distribute its important tasks among other Computers. The state of each computer regarding core storage usage and central processor utilization is reported to the E.C. This is possible through dividing each computer memory into pages and keeping the E.C. regularly notified on the number of ~used pages in each computer. The amo~t of central processor utilization could be measured by the time interval it spends looping in its sheduler each second. This information is stored in a status table arranged at specific locations in the E.C. memory. Knowing the above parametera the E.C. will manage the load distribution and resource sharing; however, the actual job scheduling and execution is left for the local executives. All intercomputer requests will be first reported to the E.C. which will choose the moat appropriate computer to handle the job of the requesting computer, the criteria might be equal loading or faster throughout. A summary of the steps involved in the network management ia given below, a) The requesting computer comm~icatea a tixed amo~t of information specifying its demands to a fixed bufter in the memory of the E.C. The latter will then use the status table to choose the most appropriate computer to handle the request. b) The E.C. transmits the results of its analysis to the requesting computer which is received at a specific butfer in the memory of the latter. c) The requesting computer will transmit the job to the chosen computer through their respective D.B.A. When the transmission is completed an interrupt aignal for both computers is established. For the receiving computer it notifies its local executive that an additional job is received and has to be scheduled for execution.
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If the r.e celved job is in machine language and it involve. a change in the base sector addresses due to the transfer, the local executive will have to correct for any confusion that may arise due to the addressing modes of the l6-hit minicomputers (3). To make this correction easier it might be necessary to separate progr~s from data and divide the base sector to section. that are dynamically alloted to the transmitted programs. The data transmitted does not need to undergo any correction and would be directly available for processing. The transmission Complete interrupt would inform the sending computer that transfer ha. _lIleti, _.uge ah...]. be cl14lcked. uti ..teara,. tree.d _d r_aed. d) The structure of the messages transmitted should have a fixed header containing key information such as the source computer, type of information transferred, requested action on the transmitted information; followed by the message proper and then checking data, After the receiver computer analyzed the message transferred for e~ror. i\ shed~leB processing or requests retransmission through the E.C. Communication between the network computers and the E.C. includes other types of information transfers such as I Failure reporting and status reporting. This is clear from the interrupt analysis flow chart shown in Fig. (6a). The status information is first identified as to its origin and then transferred to the corresponding slot in the status table. For failure reporting highest priority is given in transmission and analysis. Then the bus is granted for the back-up action and end of transmission interrupt would cause the E.C. to respond by giving the bus to the next request in the bus queue table. The part of the memory map of the E.C. holding the network management progr&ms is shown in Fig. (6b). 4. 4.1
SYST.Df ANALYSIS
Preliminary Objectives of the Network
The main two criteria for network evaluation are a) I{aximum utilization of available hardware which could be measured by the computational throughput and tbe response time. b) The increased reliability and fail-soft characteristics. This could be measured by the reduction of overall performance as a result of an element failure. The above two requirements affect the syste. integration methods both in software and hardware. The first point is mainly a function of the efficiency of the network executive .oftware and how it bandIes the available resources with minimum managerial overhead. The second point is a combined function of both system hardware architecture and software sophistication. For example, if an important experiment has to be serviced continuously then an automatic link should be available to connect it to the bus in case of local computer failure. Another aspect is the degree of software distribution ~ong local and Common back-up storage~
487
'bho ,N ...ca Id eo,ie. of im,oE1..~t hDtt.iculIt in more than one back-up storage, which are available for retrieval and use. That is to say duplication and automatic switch over. 4.2
Increase of System Capabilities a. a Result of Integration
The presence of communication pathes &mong the different computers of the network would lead to the availability of more computational power for each experiment. This is mainly due to the difference in the timing of peak loads on the different machines. Computers doing control functions are loaded heavily during transients while other computers doing data acquisition for physics experiments are usually loaded more heavily when the experimental facilities are at steady state. Hypothetical loading curves are shown in Fig. (7). Consider the example of three computers used for three types of experiments as discussed ill section 3.1. If the computers were not connected then we would use l6K memory for the control Computer, 12K memory for the physics computer, and 4K memory for the heat transfer computer. However, if we have them connected in a network then it would be possible to reduce the memory capacity of these machines to 12K, 8K and 4K respectively making use of the time difference in the peak occurrence. When there will be more computers serving different experiments on the same experimental facility the difference in loading cycles would be then available tor conversational computation jobs. It is also not uncommon that some experiments are not running for few days, while setups are changed. 4.3
Bottlenecks and System Performance Evaluation
A basic bottleneck in the computer network is clearly the Common bus interconnecting the Computers and peripherals. If the bus cannot handle the data traffic quickly then memory space in different computers will be tied for longer time (e.g. when a computer wants to transfer data to common (lisc unit or to the line printer). This means t11Ut a s low bus unit may nece ssi tate the increase in core memory capacity to hold the output data for a longer time until the bus is free for the transfer. If the system becomes bus limited then we have to resort to the exchange approach for interconnecting the Computers and peripherals in a network. Other bottlenecks may be the line printer and the disc unit when the bus unit is capable of a high transfer rate and the utilization factor for each of these units is high. For the ddsc this means that its access ttroe should match the transfer rate over the bus, and for the line printer an appropriate buffer size should be used. An obvious remedy for this situation is to h"ve more than one disc unit or line printer, so that a queue will not build up in the core memories of the working computers. Queuing theory could be used to get a quantitative measure for the bus-unit loading based on typical figures for traffic volume. The bus
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unit situation could be visualized as a singleserver qu!ue 4 as shown in Fig. (S). Let n be the average arrivals per second and be the service time of an item (in this case the complete transfer of a word from one computer to another one or a common peripheral), and ~ be the standard deviation of all service times. The number of items yaiting at a given time for service is wand the number of items in the system both yaiting service or being serticed at a given time is q. If P is the facility utilization, then in the steady state
s
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c
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q•
0.25
These figures indicate that the transfer over the bus unit in the above mode will not load the system [4] • It should be noted that the above analysis are very rough estimates; more precise analysis could only be done using simulation methods combined with some statistical information, if available, regarding the modes of data transfers between the elements of the net york as handled by the proposed software operating system. 5.
DESCRIPTION OF A PLANNED NETWORK
In the ARE Atomic Energy Establishment, a center for basic scientific and applied research in Nuclear Engineering, the idea of using computers to support experiments and establishing an
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integrated information netyork came gradually since 1969. The stimulating factor was the appearance of small, reasonably priced, fast, and highly reliable computers using integrated circuits. It took about tyO years to acquire and make operational an H-3l6 computer, from Honeyyell Information Systemf, which yas planned for on-line control experiments for nuclear reactors. This computer has 1.6 usec. cycle time, 16 bit yord, and 16 K yord of core memory, a ..all disc mass store of la2 K yord is also available. Input-output devices are a Teletype and a fast paper tape read and punch. The real time interface to serve the control experiments involves analog and digital input-output subsyst. .s, as yell as additional interrupt facilities. The reactor is scheduled to go under computer control early 1973. The design of a fey hardyare units such as an operator communication desk as yell as the application softyare yhich involved additions to the manufacturer's softyare capabilitie. ya. developed by an in-house group. After acquiring the above computer, interest of other research groups in the use of computers to support their experiments yas raised. Physicists involved in spectrometry and neutron diffraction studies as yell as thermal engineers doing york on heat transfer studies yanted to computerize their experiments. A pulse high analysis demonstration yas made by interfaCing a locally designed ADC to the IT-3l6 and using an ordinary scope for spectrum display. A second computer yas then planned for 1973 and the choice yas for an H-716 from the same manufacturer. A ruling factor in its favour yas the softyare compatability yith the existing one. This new computer has a tyO times shorter cycle time and a D.K.A. yhereas the H-316 has only a DHC (Direct HultipleEControl). It has also some useful hardyare additions to make it more poyerful in real time applications, such as a standard fast clock and stack facilities as well as a more poyerful operating softYare. This computer yill serve, for the time being, the physics and thermal experiments on time sharing basis. parallel connection betyeen the tyO computers yill be tried using an interface along the same lines with that discussed in this paper as yell as the additions needed to the operating system for both computers to manage the intercomputer activities. The distance between the tyO computers yill be about 200 meters and parallel transmission yill be used. This project is planned for 1973-1974. A large scientific computer ICL-1905 at Cairo Ubiversity is available to provide large scientific data processing. Communication b9tween this computer and one of the local computers over a telephone line will be attempted. The operating system of the ICL-1905 could support ASCII terminals and the expected rate of transmission would be 600-1200 bauds. The next step is the organization of a Common bUB network and the installation of the executive computer, which is planned for 1975. EXpensive equipment such aB large cap~city multitrack disc stores and line printer will be connected to the network after the executive computer
is introdu ced. The execut ive comput er will support about eight teletyp es connec ted direct ly to it which will serve as conver sationa l comput ation termin als in Basic languag e for the labora tories and will also contro l the transm ission of more involve d program s in FORTRAN over the telephone line to the scient ific comput er and receiving the result s back for printin g. 1
REFERENCES Franz, L. Alt, Worris Rubino ff, Editor s, A~ances in compu ters, Vol. 4, Sectio n on Multip le Comput er System s, Academic Press, New York 1963.
2
C.G. Bell and Al., Comput er networ ks, Compu ter, septem ber/Oc tober 1970.
3
J.J. Morris , What to expect when you scale
down to a min*c~p.bet1,Control Engine ering, Septem ber 1970. 4
James Martin , Design of a real time comput er System ,Prentt ee-Hal l Inc., Englew ood Cliffs . New Jersey 1967.
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