The present invention relates to microprocessor controlled embedded systems and, in particular, to the safety critical monitoring thereof.
Microprocessor controlled embedded systems are prevalent in medical devices, such as MRI imaging systems, blood testing equipment, etc., where it is now necessary to provide a safety critical environment for the protection of patients. As shown in FIG. 1, in a typical embodiment the system 2 sits between the specific application system 1 and an application specific user interface 3. In systems of this type, as shown in more detail in FIG. 2, application specific program logic resides permanently within a static memory 8 (non-volatile ROM or RAM). Along with the application specific program logic, the system includes an embedded operating system which is either a single process executive or multi-tasking executive system. The operating system is responsible for controlling the system interrupts, input/output control and the scheduling of the specific application tasks on a time or performance basis. The operating system operates with the microprocessor 5 which is part of the central processing unit of the system along with a random access memory and an input/output circuit 7 which communicate on a bus 6.
The application specific program logic is responsible for performing all functional operations, as well as for directly handling input and output of the information and control required for the specific application system utilizing the embedded system. The operating system is a stand-alone program or set of programs with a specifically defined interface for connecting it to the application specific program logic. The application specific program logic has the required interface logic to link it with the operating system. In conventional embedded systems, the operating system has no knowledge of the performance requirements of the application specific program logic or the specific application system, but simply acts as the controller for the central processing unit.