How to Avoid Complicated If-clause Structure in Fortran Real-time Programming

Abstract

The paper deals with an extension to an existing FORTRAN implementation (1) to incorporate the following features:The first set of calls enables the user to alter the program flow in one activity from outside. Up to now this feature was used in the following two cases.1. Normally in multitasking the whole stack area is divided into equal portions of task-stacks. Otherwise the user has to specify the task-stack area for each of his user tasks. Therefore it is necessary to keep the number of tasks as small as possible. To overcome this difficulty an activity is created and put in the running state doing one of a set of computations of some lower priority. Then the computations actually performed can be influenced from outside without programming in complicated conditional branching.2. The proper releasing of resources in aborting tasks is a severe problem. Normally only the target task has access to information concerning specific actions that have to be performed before releasing the resources. The possibility is provided to direct the task that is to be aborted to a computation which will shut down the resources in a controlled way.The second set of calls is an approach to implement the concept of the conditional critical regions (2) and is currently used to assure that only one activity has access to user devices such as CAMAC, Display etc. at one time.This could be achieved without modifying the general scheme of the existing task scheduler (1).