ALAS(ID:5345/ala006)

Continuous simulation language 

for Asynchronous Look Ahead Simulator


simulation system
References:
  • Ulrich, E. G. "Time sequenced logical simulation based on circuit delay and selective tracing of active network paths" view details Abstract: MANY PUBLISHED efforts in the field of logical simulation indicate that the programming concept of “compiling and executing” is the most frequently used foundation for the construction of simulation programs. The technique to be described here represents a complete departure from the concept of “compiling and executing”. The basic framework for the simulation method to be presented is simply a close imitation of the structure and operation of a logical network. Applying this concept leads to a realistically operating “general purpose” simulator. The resulting simulation possibilities are—at least with respect to the field of logical simulation—relatively unexplored and unexploited. Simulation in other fields, e.g., the simulation of nerve nets by Reiss1, has preceded the field of logical simulation in taking advantage of the structure and operation of (neural) networks. The first success in applying these methods to the field of logical simulation has been reported by Case, et al2.

          in [ACM] Proceedings of the 1965 20th National Conference 1965 , Cleveland, Ohio, United States view details
  • Leavenworth, B. review of Ulrich 1965 view details Abstract: This paper describes a general purpose simulation program called ALAS (Asynchronous Look Ahead Simulator) written for the IBM 7094, and used for simulation of logical networks. Input to Alias consists of logical equations, digital elements and their parameters. Associated with each element is its delay time, and a specification of its logical operation in terms of given primitives (AND, OR, NAND, NOR). The user apparently has considerable flexibility in defining how the input equations are to be interpreted by the program (for example, he may restrict acceptable characters within equations to be certain numbers, letters and symbols). Although this implies a metalanguage to specify such rules, it is not clear exactly how this is done, since no examples are given of equations or interpretation specifications. Also implied is some type of translation or macrogeneration of the logical equations. This would be at variance with the author's assertion that his technique "represents a complete departure from the concept of compiling and executing."

    The main value of the paper appears to be its clearly; written exposition of what is called the "look-ahead" simu ration technique. This technique is similar to the timing administration used in simulation languages such as SIMSCRIPT and GPSS (not referenced). One departure is that all element delays are assumed to be smaller than a parameter "T" supplied by the user. Longer delays are handler on an exception basis. An advantage of this approach is that the events queue, here called the At-loop, can be maintained as a table rather than as a list.

    In summary, it would seem that the main advantage of ALAS over a general purpose language such as SIMSCRIPT is its specialized orientation toward logical simulation, will greater convenience in specifying equations and element delays without the need of explicit programming. However the convenience factor is difficult to judge because the paper does not give sufficient information on input procedures and formats.

    REFERENCES
    [1] General Purpose Systems Simulator II, Reference Manual. International Business Machines Corp.
    [2] MARKOWITZ, H. M., HAUSNER, B., AND KARR, H. W., SIMSCRIPT -- A Simulation Programming Language, The RAND Corporation, 1963, Prentice-Hall, Inc., Englewood Cliffs, N. J.

          in ACM Computing Reviews 7(01) January-February 1966 view details
  • Oshipkovitz, Samuel "An asynchronous look-ahead digital simulation language" (M.Sc. Thesis) Case Inst. of Technology, Cleveland, Ohio, 1967 view details Abstract: ALAS (Asynchronous Look-Ahead Simulator) 1107 is an implementation of a digital systems simulation language. This implementation uses and notes only the changes of states of the system and resultant ejects. By contrast the usual method re-evaluates all nodes. The system demonstrated here is an asychronous ("interrupt driven") look-ahead system and thus the electronic timing (internal delays) of the simulated devices is considered. The simulator was written in a combination of ALGOL 60 and SLEUTH II (UNIVAC 1107 assembly language) . The description of a digital system in this language is described with its input and output nodes in a single statement, the order of these statements being unimportant. Coding in this digital simulation language is simple, enabling any engineer to learn to program its use in a matter of minutes. Provision is made for adding additional devices and/or internal delay parameters to the system.
          in ACM Computing Reviews 7(01) January-February 1966 view details