Patent #5,469,571 "Operating System Architecture using Multiple Priority Light Weight kernel Task-based Interrupt Handling." Granted November 21, 1995 One of the most difficult challenges faced by designers of embedded systems is to meet real-time performance requirements. The interaction of multiple input-output (I/O) devices and system processes gives rise to complexities in timing and can degrade system performance. LynuxWorks™ developed a new way of managing kernel threads and priority processing, and was awarded a patent for its technology, which is part of the LynxOS® real-time operating system. The invention takes a unique approach to handling hardware events in a real-time environment, and allows complex multi-process and multi-threaded applications to respond in a predictable and timely manner. Processes and priorities In multi-tasking operating systems, such as UNIX®, each process or program receives a priority which helps determine when it will run. In general, higher priority processes run before lower ones. Once a process is running, it has the full attention of the CPU. The OS changes which process is executing by one of three means: Yielding The process itself voluntarily gives up the CPU [...]

a white paper by Greg Rose First Choose a processor that has an on-chip MMU. Second Choose an operating system that fully supports the MMU. These two choices just might give you a good night sleep when your product is deployed. System designers constantly face engineering trade-offs between system speed, integrity, and maintainability. With the increasing performance of microprocessors, and the ease of systems configuration and enhancement in software, as opposed to hardware, more of the actual system is implemented in software. Products are now designed by teams of programmers, working on multiple programs, with all the programs coexisting on one microprocessor. With more programs running on one processor, a practice of "locking the doors" becomes necessary. Without protection, a single program bug could leave a trail of destruction that would compromise the integrity of the entire system. Understanding Bugs Despite the best effort of software engineers, it is an accepted fact that all software has bugs. Many software bugs live happily in a system as long as a given set of conditions are not encountered that cause the bugs to show [...]