The figure above is the high-level state transition diagram for an instance of a real-time executive hosted on one processor. There is actually one level higher than this, which shows that the multiple processors in a system each have an instance of this state machine, where all these state machines are concurrent and engage in a concensus protocol. This state machine shows that each individual processor goes through a series of test, initialization and synchronization states in order to reach an operational state. Fault events may occur, which may cause the state machine to repeat some of these steps or to enter an OFF state.
While each instance of the executive on a processor is in the OPERATION state, it executes one or more real-time periodic application processes. Each periodic process itself is modeled as a state machine like the ones shown above, where events such as timer interrupts and kernel service calls cause the state of a process to change. The figure above illustrates how a set of concurrent application processes, viewed as a collection of concurrent state machines, defines the behavior of a kernel instance while it is in the OPERATION state.
This is a simplified version of the architecture used in the automatically configured executives that support applications specified using the MetaH architecture specification language. In this case all the details of configuring the underlying state machine executive are handled by the tools, and the user sees a higher-level real-time process architecture style.