A methodology for specifying and proving assertions about time in higher-level language programs is described. The approach develops three ideas: the distinction between, and treatment of, both real time and computer times; the use of upper and lower bounds on the execution times of program elements; and a simple extension of Hoare logic to include the e ects of the passage of real time. Schemas and examples of timing bounds and assertions are presented for a variety of di erent statement types and programs, such as conventional sequential programs, including loops, time-related statements such as delay, concurrent programs with synchronization, and software in the presence of interrupts. Examples of assertions that are proven include deadlines, timing invariants for periodic processes, and the speci cation of time-based events such as those needed for the recognition of single and double clicks from a mouse button.

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Abstract. Periodic processes are major parts of many real-time embedded computer applications. The programming language Ada permits programming simple periodic processes, hut it has some serious limitations; producing Ada programs with real-time performance comparable to those produced to date using traditional cyclic executives requires resorting to techniques that are specific to one machine or compiler. We present and evaluate the cyclic executive model for controlling periodic processes. The features and limitations of Ada for programming cyclic executive software are discussed and demonstrated, and some practical techniques for circumventing Ada limitations are described.

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