For managing traffic speed and capacity on its TGV Nord line between Paris and Lille and on the future Transchannel link, the French National Railroad (SNCF) uses an automatic train control system named TVM 430. This system displays instructions for train engineers and checks that these instructions are properly executed. TVM 430 is a fully automated system that was developed by CSEE (Compagnie des Signaux). It comprises train and ground based modules, each containing several embedded 58020 based boards communicating over a VME bus.

Part of the TVM 430 project entailed the development of a simulator. The user prepares test procedures that describe the environment and that define the expected actions according to time, train speed, and location. Based on these test procedures, the simulator generates the systems inputs and records the outputs. A completely automated model of the environment is thereby created. The simulator is first used to test the system on a functional level on the developer's machine. Real time execution is later validated on the target equipment.

The core of the environment simulator comprises 80,000 lines of code and was completed by a 4 person team in one year. None of the programmers had previous experience with Ada; the necessary training was accomplished through seminars conducted by Alsys. Although the simulator was developed for the TVM 430, it provides a convenient and inexpensive way to test many kinds of embedded systems. Adaptation for other environments will require only a small amount of work, thanks to the modular nature of the Alsys software and the support that Ada offers for reusability.

The simulator was first developed on VAX where it was used for functional level testing. It was the ported to the target equipment in two steps: First to a 58020 based machine, using the Alsys VAX hosted cross compiler. Then to a PC compatible. A VME/AT coupler was developed to allow all of the functions of the simulator to be available on a single machine.

In contrast with other industrial language, Ada can be used as early as the preliminary design stage. The application architecture can be defined rapidly but rigorously; Ada unit specification from body and Alsys' multilibrary environment ease the task of producing a prototype. Coding in Ada may require more time than is necessary with other industrial languages, but that is because the language enforced checking will reveal errors early and in effect, perform a large part of integration testing. Thus the testing and system integration phase proceeds much more rapidly than with the other languages.

The tasking facilities of Ada proved to be extremely useful, since it allowed the system's logically independent processing to be expressed in high level and portable terms. The readability promoted by Ada also proved to be a major benefit. The success of the TVM 430 simulator has led to Ada's adoption by CSEE in several other applications, including computer integrated manufacturing and additional prototypes.

Marie France Mignon and Florence Lescroart
Alsys SA
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