RTEMS Ada User's Guide
In multiprocessor real-time systems, new requirements, such as sharing data and global resources between processors, are introduced. This requires an efficient and reliable communications vehicle which allows all processors to communicate with each other as necessary. In addition, the ramifications of multiple processors affect each and every characteristic of a real-time system, almost always making them more complicated.
RTEMS addresses these issues by providing simple and flexible real-time multiprocessing capabilities. The executive easily lends itself to both tightly-coupled and loosely-coupled configurations of the target system hardware. In addition, RTEMS supports systems composed of both homogeneous and heterogeneous mixtures of processors and target boards.
A major design goal of the RTEMS executive was to transcend the physical boundaries of the target hardware configuration. This goal is achieved by presenting the application software with a logical view of the target system where the boundaries between processor nodes are transparent. As a result, the application developer may designate objects such as tasks, queues, events, signals, semaphores, and memory blocks as global objects. These global objects may then be accessed by any task regardless of the physical location of the object and the accessing task. RTEMS automatically determines that the object being accessed resides on another processor and performs the actions required to access the desired object. Simply stated, RTEMS allows the entire system, both hardware and software, to be viewed logically as a single system.
Multiprocessing operations are transparent at the application level. Operations on remote objects are implicitly processed as remote procedure calls. Although remote operations on objects are supported from Ada tasks, the calls used to support the multiprocessing communications should be implemented in C and are not supported in the Ada binding. Since there is no Ada binding for RTEMS multiprocessing support services, all examples and data structures shown in this chapter are in C.
RTEMS Ada User's Guide
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