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Remarks

Many tools exist that simplify implementation of real time systems for control. The most important of these are Real Time Operating Systems (RTOSs), which are used for the actual implementation of real time controllers. Many of these incorporate the fixed priority schedulers as well as many forms of priority inheritance protocols. Some of the more popular RTOSs are VxWorks1.7, QNX1.8, and recently Real Time Linux1.9 - a kernel level modification to Linux1.10.

More readily available operating systems such as Windows 9x and NT can be converted into a real time systems via third party software. However, at best these systems can provide soft real time support in that they do not support priority inheritance protocols but rather have a ``randomizing'' protocol which, in the event of blocking, will begin randomizing priorities until all blocked tasks execute. Reportedly, some further third (fourth?) party software may exist that appears to fix this problem to some degree. Furthermore, complex device drivers are needed for these systems and have been found to cause unnecessary delays that further make these systems too non-deterministic for time critical control.

In what follows, a controller implementation solution has been implemented at the University of Virginia Rotating Machinery and Controls Laboratory in a novel controls implementation platform using Real Time Linux and a set of networked personal computers.


next up previous
Next: The Real Time Controls Up: Real Time Systems Previous: Schedulability Analysis
Michael Barabanov 2001-06-19