Engineering Papers⌕ Search

Engineering topics

Knight, J. C.

Publications and source records attributed to Knight, J. C..

32 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

PASCAL/48 reference manual

PASCAL/48 is a programming language for the Intel MCS-48 series of microcomputers. In particular, it can be used with the Intel 8748. It is designed to allow the programmer to control most of the instructions being generated and the allocation of storage. The language can be used instead of ASSEMBLY language in most applications while allowing the user the necessary degree of control over hardware resources. Although it is called PASCAL/48, the language differs in many ways from PASCAL. The program structure and statements of the two languages are similar, but the expression mechanism and data types are different. The PASCAL/48 cross-compiler is written in PASCAL and runs on the CDC CYBER NOS system. It generates object code in Intel hexadecimal format that can be used to program the MCS-48 series of microcomputers. This reference manual defines the language, describes the predeclared procedures, lists error messages, illustrates use, and includes language syntax diagrams.

Knight, J. C.↗
NASA NTRS1983

A framework for software fault tolerance in real-time systems

A classification scheme for errors and a technique for the provision of software fault tolerance in cyclic real-time systems is presented. The technique requires that the process structure of a system be represented by a synchronization graph which is used by an executive as a specification of the relative times at which they will communicate during execution. Communication between concurrent processes is severely limited and may only take place between processes engaged in an exchange. A history of error occurrences is maintained by an error handler. When an error is detected, the error handler classifies it using the error history information and then initiates appropriate recovery action.

Anderson, T.↗
NASA NTRS1983

The implementation and use of Ada on distributed systems with reliability requirements

The issues involved in the use of the programming language Ada on distributed systems are discussed. The effects of Ada programs on hardware failures such as loss of a processor are emphasized. It is shown that many Ada language elements are not well suited to this environment. Processor failure can easily lead to difficulties on those processors which remain. As an example, the calling task in a rendezvous may be suspended forever if the processor executing the serving task fails. A mechanism for detecting failure is proposed and changes to the Ada run time support system are suggested which avoid most of the difficulties. Ada program structures are defined which allow programs to reconfigure and continue to provide service following processor failure.

Reynolds, P. F.↗
NASA NTRS1983

On the engineering of crucial software

The various aspects of the conventional software development cycle are examined. This cycle was the basis of the augmented approach contained in the original grant proposal. This cycle was found inadequate for crucial software development, and the justification for this opinion is presented. Several possible enhancements to the conventional software cycle are discussed. Software fault tolerance, a possible enhancement of major importance, is discussed separately. Formal verification using mathematical proof is considered. Automatic programming is a radical alternative to the conventional cycle and is discussed. Recommendations for a comprehensive approach are presented, and various experiments which could be conducted in AIRLAB are described.

Pratt, T. W.↗
NASA NTRS1983

Software fault tolerance for real-time avionics systems

Avionics systems have very high reliability requirements and are therefore prime candidates for the inclusion of fault tolerance techniques. In order to provide tolerance to software faults, some form of state restoration is usually advocated as a means of recovery. State restoration can be very expensive for systems which utilize concurrent processes. The concurrency present in most avionics systems and the further difficulties introduced by timing constraints imply that providing tolerance for software faults may be inordinately expensive or complex. A straightforward pragmatic approach to software fault tolerance which is believed to be applicable to many real-time avionics systems is proposed. A classification system for software errors is presented together with approaches to recovery and continued service for each error type.

Anderson, T.↗
NASA NTRS1983

Fault tolerant distributed systems using Ada

This paper discusses the use of Ada on distributed systems in which failure of processors has to be tolerated. It is assumed that communication between tasks on separate processors will take place using the facilities of the Ada language, primarily the rendezvous. It is shown that there are numerous aspects of the language which make its use on a distributed system very difficult. The issues are raised from the desire to be able to recover, reconfigure, and provide continued service in the presence of hardware failure. For example, if a rendezvous takes place between two tasks on different processors, failure of the processor executing the serving task will cause the calling task to be permanently suspended because the rendezvous will never end. Extensive modifications to the execution support required for Ada are proposed which provide all the necessary facilities for programs written in Ada to withstand arbitrary processor failure. Mechanisms are suggested to allow processor failure to be detected and for tasks which would be permanently suspended to be released. Provided the required program structures are used, continued processing can be provided.

Knight, J. C.↗
NASA NTRS1982

The implementation and use of Ada on distributed systems with high reliability requirements

The use and implementation of Ada in distributed environments in which the hardware components are assumed to be unreliable is investigated. The possibility that a distributed system can be programmed entirely in Ada so that the individual tasks of the system are unconcerned with which processor they are executing on, and that failures can occur in the underlying hardware is considered. The reduced cost of computer hardware and the advantages of distributed processing (for example, increased reliability through redundancy and greater flexibility) indicate that many aerospace computer systems can be distributed. The use of Ada and distributed systems is a good combination for aerospace embedded systems.

Knight, J. C.↗
NASA NTRS1982

Production of Reliable Flight Crucial Software: Validation Methods Research for Fault Tolerant Avionics and Control Systems Sub-Working Group Meeting

The state of the art in the production of crucial software for flight control applications was addressed. The association between reliability metrics and software is considered. Thirteen software development projects are discussed. A short term need for research in the areas of tool development and software fault tolerance was indicated. For the long term, research in format verification or proof methods was recommended. Formal specification and software reliability modeling, were recommended as topics for both short and long term research.

Dunham, J. R.↗
NASA NTRS1980

A translator writing system for microcomputer high-level languages and assemblers

In order to implement high level languages whenever possible, a translator writing system of advanced design was developed. It is intended for routine production use by many programmers working on different projects. As well as a fairly conventional parser generator, it includes a system for the rapid generation of table driven code generators. The parser generator was developed from a prototype version. The translator writing system includes various tools for the management of the source text of a compiler under construction. In addition, it supplies various default source code sections so that its output is always compilable and executable. The system thereby encourages iterative enhancement as a development methodology by ensuring an executable program from the earliest stages of a compiler development project. The translator writing system includes PASCAL/48 compiler, three assemblers, and two compilers for a subset of HAL/S.

Collins, W. R.↗
NASA NTRS1978

The current status of microcomputer arrays

Some research projects on microcomputer arrays are at the stage of constructing hardware, while others are at the design and planning stages. A general overview of the topic is followed by a more detailed discussion of three projects whose purposes are specifically scientific computation.

Knight, J. C.↗
NASA NTRS1978

The current status of super computers

In this paper, commercially available super computers are surveyed. Computer performance in general is limited by circuit speeds and physical size. Assuming the use of the fastest technology, super computers typically use parallelism in the form of either vector processing or array processing to obtain performance. The Burroughs Scientific Processor is an array computer with 16 separate processors, the Cray-1 and CDC STAR-100 are vector processors, the Goodyear Aerospace STARAN is an array processor with up to 8192 single bit processors, and the Systems Development Corporation PEPE is a collection of up to 288 separate processors.

Knight, J. C.↗
NASA NTRS1975

System balance analysis for vector computers

The availability of vector processors capable of sustaining computing rates of 10 to the 8th power arithmetic results pers second raised the question of whether peripheral storage devices representing current technology can keep such processors supplied with data. By examining the solution of a large banded linear system on these computers, it was found that even under ideal conditions, the processors will frequently be waiting for problem data.

Knight, J. C.↗
NASA NTRS1968

Study of Behavior of Sterols at Interfaces

Behavior of sterols and sterol acetates on various types of interfaces indicates that the function of a sterol depends upon a surface orientation and surface energy of the interface. Column-chromatographic techniques determine the retention volume of various sterols under standard conditions.

Klein, P. D.↗