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<H2><A NAME="SECTION00123000000000000000">
Remarks</A>
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<P>
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 VxWorks<A NAME="tex2html13"
HREF="footnode.html#foot271"><SUP>1.7</SUP></A>,
QNX<A NAME="tex2html14"
HREF="footnode.html#foot272"><SUP>1.8</SUP></A>, and recently Real Time
Linux<A NAME="tex2html15"
HREF="footnode.html#foot273"><SUP>1.9</SUP></A> - a kernel level
modification to Linux<A NAME="tex2html16"
HREF="footnode.html#foot274"><SUP>1.10</SUP></A>.
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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.
<P>
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.
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<ADDRESS>
Michael Barabanov
2001-06-19
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