A CAMAC-Based Intelligent Subsystem for Atlas Example Application: Cryogenic Monitoring and Control
TL;DR: A subunit of the CAMAC accelerator control system of ATLAS for monitoring and, eventually, controlling the cryogenic refrigeration and distribution facility is under development, the first application of a philosophy of distributed intelligence which will be applied throughout the ATLAS control system.
Abstract: A subunit of the CAMAC accelerator control system of ATLAS for monitoring and, eventually, controlling the cryogenic refrigeration and distribution facility is under development. This development is the first application of a philosophy of distributed intelligence which will be applied throughout the ATLAS control system. The control concept is that of an intelligent subunit of the existing ATLAS CAMAC control highway. A single board computer resides in an auxiliary crate controller which allows access to all devices within the crate. The local SBC can communicate to the host over the CAMAC highway via a protocol involving the use of memory in the SBC which can be accessed from the host in a DMA mode. This provides a mechanism for global communications, such as for alarm conditions, as well as allowing the cryogenic system to respond to the demands of the accelerator system.
Summary (2 min read)
Introduction ATLAS 
- , the Argonne Tandem-Linac Accelerator System, is a major expansion of an existing heavy-ion accelerator facility which consists of an electrostatic Van de Graaff tandem accelerator and a prototype superconducting linear booster accelerator.
- The superconducting linac control system is a CAMAC-based system with an enhanced Digital Equipment PDP 11/34 computer as the central control computer.
- The CAMAC system is configured cs a byte-serial multi-crate highway interfaced to the central computer via a serial highway driver residing in a unibus memory-mapped crate.
- This effect occurs both due to the increased number of devices which must be monitored and controlled but also because the much more complex accelerator system requires more computing support in order to allow the staff, which has not increased in size significantly, to efficiently operate the f ;:ility.
- The ATLAS facility contains a number of complex subsystems which can significantly benefit from increased automation and computer control.
System Design Considerations
- There sre many possible approaches which may be used to achieve such a goal and the proper choice is often strongly influenced not onlyl by local personal biases but the environment, both hardware and software, which presently exists.
- The following points were requirements which the enhanced system has been designed to satisfy: I. We felt that the major investment in hardware and software which had already gone into making their facility one of the moat automated heavy-ion facilities existing could not be abandoned.the authors.the authors.
3. The congestion on the serial highway should be kept as low as possible to allow for future activities.
- The reliability of the monitoring and control of the subsystems mentioned before should be high.
- This requirement essentially rules out the use of the central computer since its reliability.
- Is compromised by the higher failure rate of disc drives, line printers, terminals and other peripherals, not to mention system crashes that occur during such activities as program development.
All choices have disadvantages. of this approach Include:
- The elaborate libraries of control functions which have been developed for their RSX-based system cannot be used in the microprocessor environment the authors have chosen.
- Therefore program development has been slower than might have been otherwise possible.
Hardware and Software Implementation
- The microprocessor chosen for implementing this concept was the Digital Equipment SBC 11/21 single board computer.
- This allows development and debugging using RAH memory which can latsr be converted into PROM memory allowing complete stand-alone operation independent of the rest of the control system.
- The Fsicon resides in and Is interfaced into the CAMAC crate through a Kinetics System 3921 crate controller operating in the auxiliary mode.
- The CAMAC-DMA unit is a Kinetics System 3825 Da taway Communications Link.
- This feature is accomplished via switches in the compile and link cycles.
The Cryogenic Monitoring and Control System
- The cryogenic monitoring and control system is the first application of the design philosophy described above.
- The implementation of this system has allowed us to break the task into three phases which will be.
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