Handling interrupts in Ada 9X

Abstract

Interrupt handlers are an important component of many real-time applications. Efficient implementation of interrupt handlers is often critical in such applications. The Ada 83/87 [1] model of task entries as interrupt handlers did not always meet the needs of the real-time community for efficient interrupt handlers so vendors provided special packages which addressed these needs. This situation led to the proliferation of incompatible interrupt handling mechanisms across multiple vendors.

Ada 9X [2] responds to the need for an efficient interrupt handling mechanism with the introduction of protected procedures as interrupt handlers. In addition, Ada 9X offers the user the facilities to both statically and dynamically attach interrupts to protected procedures.

The next section of this paper explains the Ada 83/87 interrupt model and some of its deficiencies. The discussion then proceeds to show how these problems are addressed in Ada 9X. This explanation includes an overview of protected types and a complete explanation of interrupt handlers in Ada 9X. The paper concludes with a description of what is permitted in an implementation and the effects on the user.