A way of programming real-time systems is described which inverts the usual image of parallel processes: instead of processes which are ordinarily running and which wait occasionally in order to synchronize with other cooperating processes, ``intervention schedules'' are ordinarily waiting and run nonpreemptibly, triggered by events, which may be external (modeling hardware interrupts) or generated by other intervention schedules. In order for nonpreemptive scheduling to make sense, the maximum period of time for which any event in an intervention schedule runs must be carefully controlled. This and other aspects of the model are considered, and it is compared with more traditional models of parallel processes, and with message passing models. Programming language features to support this programmming model are discussed. Strengths and limitations of the model are discussed.

Symbolic execution can be a powerful aid for microprogram development. This note describes a symbolic microprograni simulator which is used in developing microprograms for a signal processor and gives a brief example of its use. Implementation issues and cost effectiveness of this approach are also discussed.